NCSU PDIC

Plants Pests and Pathogens 2012 Starts Next Tuesday, February 28

2012-02-22T11:49:00.000-05:00

Next Tuesday February 28 we kick off the 2012 Season of Plants Pests and Pathogens with Dr. Larry Grand, who will speak about mushrooms and other macrofungi. Dr. Grand is part of a multidisciplinary team assessing fungal biodiversity in North Carolina state parks and the Great Smoky Mountains National Park.

Plants, Pests and Pathogens is an in-service training program for Horticulture Extension Agents and Extension Master Gardeners.

The Plants, Pests, and Pathogen sessions will be conducted on the fourth Tuesday of February, April, June, August, and October 2012 from 10:00 am to 12:00 pm. Every session includes a discussion of current plant disease and insect problems by the Plant Disease and Insect Clinic's Mike Munster and Dave Stephan.

Find out about the many other exciting presentations planned for this year by checking out the Master Gardener Plants Pests and pathogens webpage. We hope to see you on-line!

Log On To February meeting:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261509564719

General information:

http://www.ces.ncsu.edu/depts/hort/garden/PlantsPestsPathogens/index.html

Info for Master Gardeners

http://www.ncsugarden.com/subpages/697.html

Info for agents

http://www.ncsugarden.com/subpages/1791.html

Rhizoctonia Web Blight on Boston Fern

2012-02-21T15:10:00.001-05:00

The Boston ferns that will adorn our porches and decks in a couple of months are being grown in greenhouses now. Ferns are easy to grow, but they do have a few disease problems. This week, we received a Boston fern from a greenhouse producer who was concerned about leaflets that were blackened and blighted, especially in the interior of the plant. These symptoms are typical of web blight (aerial blight) caused by the fungus Rhizoctonia. We typically think of Rhizoctonia as being a soilborne pathogen of roots, stems, and seedlings, but it causes foliar blights on several hosts, including Boston fern. The presence of Rhizoctonia on the leaves was confirmed microscopically.

Hyphae of Rhizoctonia (Photo: M.J. Munster)

Web blight begins as irregular brown lesions on the fronds growing in the interior of the plant.

Web blight symptoms (Photo: M.J. Munster)

Eventually, these lesions expand, causing the interior and lower fronds to turn black and die. The mycelium of the fungus can be seen as a web-like coating on the foliage.

Web blight is favored by high relative humidity. To control this disease, improve ventilation and make sure irrigation is timed to avoid prolonged leaf wetness. Wider plant spacing and hanging the plants will also help to improve air circulation and promote drying. Make sure to bag and discard diseased plants, and sweep up fallen leaflets to prevent inoculum from spreading to healthy plants. Greenhouse growers should always sanitize surfaces between crops, and be sure to use sterile potting media and sterile pots when planting.

Web blight is primarily a problem in a greenhouse environment. This disease is not a problem when ferns are grown indoors, as U.S. homes have notoriously low relative humidity levels. It can be a problem on outdoor ferns, especially with North Carolina's humid summers.

Sample of the Week: TSWV on Tomato

2012-02-13T10:01:00.001-05:00

TSWV symptoms (Photo: Mike Munster)

This week's sample of the week was TSWV (Tomato Spotted Wilt Virus) on greenhouse tomato plants. We received two tomato plants with black, necrotic spots on the foliage, a symptom associated with TSWV. An ELISA immunostrip test confirmed this diagnosis. We were a little surprised to see TSWV so early in the greenhouse. Early infections usually have the most severe impact on yield because they prevent flowering and fruit set. The virus is spread by thrips and thrips populations in a greenhouse should be eliminated to prevent further spreading of the virus. Infected plants will not recover and should be removed and destroyed.

TSWV Symptoms (Photo: Mike Munster)

For more information on TSWV, check out our earlier blog posting here.

Sample of the Week: Sclerotinia Stem Rot of Snapdragon

2012-02-03T17:24:00.002-05:00

Drooping snapdragons in flower bed. Jan 23, 2012.

Sclerotinia stem rot (a.k.a. Sclerotinia blight) is a disease we seldom see in ornamentals in North Carolina. The case pictured above is only the second time I've seen it from a landscape ornamental in the last three years. The cause is a cool-weather-loving fungus called Sclerotinia sclerotiorum. Although it can infect a wide range of host plants, it's best known for the damage it does on many vegetable crops. In our state the primary victim is collards, on which the disease is known as "head rot". Cabbage, lettuce, and strawberry are affected occasionally. It would be very unusual to see this disease after mid-May in North Carolina. Note that the related fungi Sclerotinia minor (the cause of Sclerotinia blight on peanuts) and Sclerotinia homeocarpa (the cause of dollar spot on turf) are comfortable with somewhat warmer temperatures.

Stem lesions and visible white mold, evidence
of the causal fungus, Sclerotinia sclerotiorum.

Diseases caused by Sclerotinia sclerotiorum are sometimes called "white mold" because of the fluffy white mycelium of the fungus that grows on affected plant parts under humid conditions.The fungus also wads itself into small, dark, hard lumps called sclerotia, which allow it to survive from season to season in the soil. It would be unwise to plant snapdragon next fall in the pictured flower bed, even if an effort is made to clean up and remove the diseased plant material. You'd also want to avoid planting flowering kale - a collard relative. There is no effective chemical control for this disease in the landscape.

Because the fungus produces airborne spores, it can sometimes even blow into greenhouses and cause stem rots on ornamentals and "collar rot" on tobacco. This is one reason it's so important to avoid leaving piles of dead plant material in and around greenhouses. Of course diseased plant material should never be composted, in this case because of the durability of the sclerotia.

Nota bene! Ojo! Vorsicht! This disease is completely different from Southern blight (Southern stem blight) caused by the unrelated fungus Sclerotiuim rolfsii. The scientific names of the fungi are confusingly similar, both cause stem rots, and both produce visible white mycelium on the plant, but there are key differences. Southern blight occurs from late spring through the heat of summer, not in the winter and early spring. Also, the mature sclerotia of Sclerotium rolfsii are tiny, round, and tan-colored (rather like radish seeds), whereas those of Sclerotinia are somewhat larger, irregular in shape, and black. Both kinds are white on the inside when cut open, and both take longer to form than the mycelium itself.

Above: Sclerotia of Sclerotinia sclerotiorum
(Photo: PP Dept. Slide Collection)

Above: Sclerotia of Sclerotium rolfsii

Sample of the Week: Tomato Triple Whammy

2012-01-27T10:44:00.001-05:00


Tomato Sample, notice the puckered leaves (Photo: E. Lookabaugh)

This week’s Sample of the Week came packing a triple threat! A client brought in two tomato plants from their greenhouse. As soon as we opened the bag, a cloud of whiteflies flew out, alerting us to culprit number 1. Whiteflies damage the foliage when they feed, resulting in yellowing and curling of the leaves. In heavy infestations, whiteflies can cause stunting of the plant, reduced vigor, and leaf drop. Prevention is the best management option for whiteflies. All incoming plants should be checked before they are introduced into the greenhouse. Once the whiteflies are established in the greenhouse, you can starve them out by removing all host plants for at least two weeks, or a more practical option is the use of sticky traps. Whiteflies are attracted to bright colors like yellow and white so hanging white or yellow sticky traps above susceptible plants can reduce population numbers.

Whitefly damage, look closely and you can see the whiteflies (Photo: E. Lookabaugh)

Upon examining the foliage, we noticed the leaves seemed stunted and distorted. Some of the leaves appeared puckered. We also saw light green etching or mottling on some of the foliage. Distorted foliage in combination with stunted new growth and mosaic or mottling of the leaves usually points toward a virus infection. We ran assays for the common viruses associated with greenhouse tomatoes and determined Tobacco Mosaic Virus (TMV) was culprit number 2. TMV is a serious threat to greenhouse plants. It is spread through contact with tools, workers’ hands, or infected plants. Pruning, tying, and transplanting are great ways to accidentally spread TMV to healthy plants in the greenhouse. TMV has a very wide host range and can survive on root and plant debris for long periods of time. Virus particles can also survive in cigarettes or chewing tobacco so workers who smoke or dip should wear gloves when handling TMV-susceptible plants. Strict prevention and sanitation programs provide the only means of controlling the disease. Use disease-resistant varieties and disease free seed/ transplants whenever possible. Encourage workers to dip hands in milk, wear gloves, or wash hands with soap and water before and after handling plants. Do not touch healthy plants after handling infected plants. Remove any nearby weeds that could harbor the virus. Infected plants and plant debris should be removed immediately.

TMV Symptoms (Photo: E. Lookabaugh)

Finally, we checked the roots to provide a complete diagnosis. Amazingly, we noticed swollen and knotted roots caused by root knot nematodes, culprit number 3! Above ground, root-knot nematodes can cause yellowing, stunting, and wilting. Usually root-knot nematodes are not a problem in greenhouse tomatoes and other plants grown in treated potting mixes. These particular plants were being used in a research study so they were being grown in soil intentionally infested with nematodes.

Root knot nematode, notice the galls on the roots (Photo: E. Lookabaugh)

Unfortunately, these tomato plants probably won’t make it. Whiteflies, TMV, and root knot nematodes can pack a serious punch to tomato plants individually-- imagine having all three!

For more information, see links below:
http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg15.htm
http://www.ipm.ucdavis.edu/PMG/r783301211.html

"It's alive!" - Scorpion found in local basement.

2012-01-23T14:25:00.002-05:00

Hentz's Striped Scorpion, Centruroides hentzi

This juvenile Centruroides hentzi (a.k.a. Hentz's striped scorpion, a.k.a. Florida striped scorpion) was found alive in a Raleigh basement last week. It would measure a little over an inch long with the tail extended. It presumably hitchhiked on luggage that had traveled to the scorpion's native range and back. This range includes Florida, southern Georgia, and the Gulf Coast of Alabama. Like most scorpions, the sting of this species is painful but not deadly, according to PDIC entomologist Dave Stephan, who made the identification and provided the information for this post. It is interesting to note that there is only one scorpion species native to North Carolina, but none to the Triangle area.

1 year Anniversary

2012-01-20T16:46:00.005-05:00

Happy Anniversary to the PDIC Blog!

This month, we are celebrating our 1 year anniversary in the world of social media! On January 21, 2011, we made our first post on Blogger, since then we have posted 47 more blog entries. A year ago, none of the members of our staff had ever blogged or tweeted in their lives. We hopped on the social media bandwagon and spent the last year figuring out how to keep the blog topics interesting and current enough to satisfy our reader's appetite for fast and easy information on plant diseases and insect pests.

A few statistics...

To date, we have posted 47 blog entries, reaching 10 different countries, and accumulated over 16,000 page views. Not too shabby if you ask us! To some bloggers these numbers may not seem too impressive, but we are slowly gaining speed and expect to have an even bigger audience by the end of 2012!

Our most popular blog topics include herbicide injury to tomatoes, geotrichum sour rot on shrink wrapped sweetpotatoes, and household molds: what hurricane Irene left behind. We are always looking for new topics so be sure to let us know if there is a topic you want to see on our next blog.

In addition to our blog, we also developed a new website that contains lots of great information. Here you can find info on how to submit samples to the clinic, videos on how to take a proper sample, links to useful websites, disease factsheets, and pest alerts. To visit our website, click here.

The goal of the blog was to educate the public on plant diseases, insect pests, and other topics of interest in the world of plant diagnostics. We hope that as time goes on, you will agree that we have, at least in part, achieved what we set out to do! We hope you have enjoyed reading our blog as much as we have enjoyed writing it!

Thanks,

The Plant Disease and Insect Clinic Staff

Be sure to follow us on Facebook and Twitter and check out our awesome twitpics!

Sample of the Week: INSV on Cyclamen

2012-01-13T15:32:00.000-05:00

INSV symptoms on cyclamen (Photo: M.J. Munster)

A potted cyclamen is a nice way to brighten up a cool windowsill in winter, but a cyclamen sample we received from a greenhouse this week did not look so pretty. The grower noted that the problem started with light-green mottling of the leaf edges. Eventually, these mottled areas turned brown and the buds died.

Necrotic spots on cyclamen, INSV symptoms (Photo: M.J. Munster)

Upon examining the plant, we observed mottling of the foliage, necrotic lesions on the leaves, and necrosis and decay of the crown. PDIC entomologist Dave Stephan also found Western flower thrips present in low numbers on the sample. We suspected INSV (Impatiens Nectrotic Spot Virus) and confirmed the diagnosis with an Agdia Immunostip test.

Positive Immunostrip Test (Photo: M.J. Munster)

INSV attacks a wide variety of hosts and is vectored by Western flower thrips (Frankliniella occidentalis), a tiny insect that feeds on leaf and flower buds, petals, and pollen. Thrips breed all year in the greenhouse and the virus can spread quickly when thrips are present. Symptoms of INSV infection vary widely from hosts to host. Typical symptoms in ornamental crops include mottling, yellowing, wilting, stem death, poor flowering, ringspots, and sunken lesions on the foliage.

Sunken necrotic lesion, INSV symptom (Photo: M.J. Munster)

Necrosis/decay of the crown (Photo: M.J. Munster)

Controlling INSV is difficult and the best management strategy is prevention. Both INSV and thrips have a very broad host range, so weed removal in and around greenhouses is an important part of prevention. Greenhouses vents should have screens to exclude thrips. Insecticides are only partially effective against thrips and virus transmission. Most systemic insecticides do not translocate well to flower parts where thrips feed, while insecticides that “kill on contact” may not reach thrips hiding deep in blossoms and buds.

Inspect and monitor all incoming plant material carefully to prevent introduction of INSV and thirps on stock plants. Any plants with suspicious symptoms should be isolated and sent to the PDIC to test for INSV infection. The virus can be spread by vegetative propagation. Since infected plants cannot be cured, and cannot be used for propagation, they should be destroyed.

For more information on thrips control, click here
For more information on INSV, click here

Sample of the Week: Canker Rot on Oak

2012-01-06T14:26:00.004-05:00

Fruiting body of Inonotus hispidus on the
trunk of an oak in Craven Co., NC. December
2011. Photos courtesy Tom Glasgow, NC
Cooperative Extension Service.

This sample actually came in last month, but we made the definitive identification this week. You might be seeing more conks (a type of fungal fruiting body) now that our deciduous trees have dropped their leaves.

Inonotus hispidus is one of many fungi capable of causing a white rot of the heartwood of trees. It is, however, one of only a few such fungi that can kill living tissues of the tree. The common name of "canker rot" is a reflection of this fact. It is widely distributed in North Carolina and the United States, and occurs on hardwood trees, especially oaks. For a technical description of this organism, see its page among the Fungus Profiles on the web site of the Larry F. Grand Mycological Herbarium.

Fruiting bodies of Inonotus hispidus can occur much farther up the trunk than what is pictured here. Also please note that the presence of these fruiting bodies indicates decay within the tree, but wood decay can be present without any externally visible signs or symptoms in a given year.

Box Blight Webinar - January 5, 2012 11 a.m. EST

2012-01-03T12:58:00.003-05:00

On Thursday January 5th at 11 am EST, NC State University will be hosting an ELLUMINATE LIVE webinar on box blight. Box blight is a disease new to the US and was recently found on boxwood in North Carolina, Virginia, and Connecticut (and now a few additional states).

This webinar will be geared towards County Agents and boxwood growers in North Carolina and adjacent states, but all interested parties are invited. There is no limit on attendance, so anyone can watch the webinar LIVE!

Dr. Kelly Ivors, who first diagnosed box blight in the US, will speak for 45 minutes, followed by questions from the audience. The session is scheduled to last an hour and a half but will be extended if necessary. Representatives from VA and other box blight positive states may make additional comments and address concerns in their states.

The webinar will be recorded and made available for viewing at any time after the webinar at the same URL given below.

Here's how to participate in the webinar:

Before the webinar, click on http://go.ncsu.edu/box_blight_webinar

The webinar will start EXACTLY at 11 am EST. Please log in a little early so that you can check your connection. You will be able to enter the session starting at 10 am EST on the day it occurs. All that you need is an up-to-date browser and internet connection. In order to test that your system configuration is acceptable, visit the Configuration Room at http://go.ncsu.edu/elluminate_config any time before the webinar. In addition, Elluminate tips can be found at http://collaborate.extension.org/wiki/Elluminate_Tips

Mistletoe, Past and Present

2011-12-21T16:38:00.010-05:00

"Everybody knows, a turkey and some mistletoe…" (1)

Leafy mistletoe in the crown of a willow oak.
Photo by Dr. Larry F. Grand

The age-old tradition of kissing under the mistletoe is well known in our culture, and most people have heard of the importance of mistletoe to the ancient Druids, for whom it served ritual and medicinal purposes (2). Many also know the berry-like fruits to be toxic to people, but according to Poisonous Plants of North Carolina, poisoning will occur only if large quantities are eaten.

Fewer people know the marvelous mistletoe story from Norse Mythology, wherein a conniving Loki arranges for a mistletoe arrow to be used to kill Balder, whom the creatures of earth were sworn not to harm. The mistletoe – which never touches the earth – was not obligated by the oath (3). On a more scientific note, mistletoe was recognized as being a parasite of its host tree as far back as the 13th century by Albertus Magnus (4), a.k.a. St. Albert the Great, who gets my vote for patron saint of plant pathology.

In North Carolina mistletoe is a common sight this time of year in oaks and other hardwoods, since it stays green even after its host tree has dropped its leaves. I've seen mistletoes recently in sycamore and even in ornamental pear. They usually appear as round sprays of leafy stems high in the crown. This makes them inconvenient for gathering as holiday decor, and people have been known to bring them down with a shotgun blast. In some cases – this seems especially common in red maple – mistletoe occurs as a trunk infection, causing a gnarling and roughening of the bark. The mistletoe shoots coming from these trunks are more accessible to would-be collectors, but are rather too short for effective decorating. Unless someone is beating me to the bigger ones.

Leafy or true mistletoes in the New World belong mostly to the genus Phoradendron. They are classified in the Viscaceae, the same family as the famous Eurasian mistletoe, Viscum album. Both are "water parasites" which take up water and dissolved minerals from their host trees but photosynthesize most of their own food. As you might imagine, this arrangement is a more serious burden for trees in the drier parts of the country than here in the Southeast. You would not likely confuse the true mistletoes with their cousins, the dwarf mistletoes (Arceuthobium spp.). Not only are their size and appearance different, but dwarf mistletoes don't occur in North Carolina, even in the seemingly suitable climate of our mountains. They do occur in western and northern U.S. states, where they can be serious pests of conifers.

Dwarf mistletoe. Photo by David Shew

If you look up mistletoe in a Spanish-English dictionary, you'll be given the word "muérdago", but in my wife's home in southern Mexico, mistletoe is referred to as "injerto". This word means "graft" and is a very apt moniker, given the xylem union between the mistletoe and its host. Interestingly, the mistletoe of my wife’s upbringing has showy flowers, much different from the inconspicuous flowers of our local types.

The mistletoe's whitish berries are eaten by birds, but the seeds pass through the birds’ digestive systems. Some are lucky enough to be deposited on thin-barked tree branches, where they are held by the seeds' sticky coating (Remember the family name Viscaceae?). After germination, instead of roots the young parasite forms structures that penetrate the branch and establish an infection. The mistletoe's shoots develop later, but are very small the first year. Growth continues in subsequent years, and the mistletoe will be with the branch for life. (6)

"Your heart's a dead tomato / splotched with moldy purple spots, Mr. Grinch." (7)

From all of us here at the Plant Disease Clinic, Happy Holidays! Please remember that we'll be closed December 26-30, 2011. We look forward to checking your tomatoes, trees, and the critters that bug you in 2012.

References
(1) Mel Tormé and Bob Wells. 1944. "The Christmas Song".
(2) Bussing, Arndt, ed. 2000. Mistletoe: The Genus Viscum. Harwood Academic Publishers. p.1
(3) Ibid., p.2
(4) Agrios, G. 1997. Plant Pathology, 4th ed. Academic Press. p.10
(6) Sinclair, W.A., and Lyon, H.H. 2005. Diseases of Trees and Shrubs, 2nd ed. Cornell University Press.
(7) Theodore "Seuss" Geisel. 1966. "You're a Mean One, Mr. Grinch".

Sample of the week: Black rot of crucifers

2011-12-16T15:43:00.002-05:00

If you are looking forward to a nice mess of collards for Christmas or greens for the first meal of the New Year, this week’s samples are for you. We received several samples of seedlings and plants in the cabbage family that had yellow or brown yellow lesions. Some of the leaves had V-shaped lesions along the margins, while other leaves also had necrotic and blackened veins.

Black rot symptoms caused by Xanthomonas campestris pv. campestris. Note V-shaped lesions on leaf margins.

Collard leaves with blackened veins. Water droplets formed at the hydathodes can be seen along the margins of the upper leaf. Photo by Lisa Rayburn.

These symptoms are typical of black rot, a common disease of crucifers (cabbage, broccoli, kale, collards, turnips, etc.) caused by the bacterium Xanthomonas campestris pv. campestris. Bacterial ooze was visible coming out of the lesions on seedlings, supporting the black rot diagnosis.

The black rot bacterium infects plants through wounds and natural openings, such as hydathodes (water pores) found on the leaf margins. Later, the bacteria invade the vascular system and spread systemically. The disease is favored by mild, wet weather and the bacteria can rapidly spread from plant to plant in splashing rain. Bacteria can be spread when plants are handled (for example, during transplanting) and they survive on and in seed and in debris in the soil.

Black rot is very difficult to control because it is systemic and because we have very few chemicals that are effective against bacteria. To reduce spread, avoid cultivation or handling when plants are wet. To prevent black rot, plant clean seeds or seedlings into areas where no crucifers have been grown for 2-3 years.

For more information see:

http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg16.htm

http://www.extension.org/pages/29925/managing-black-rot-of-cabbage-and-other-crucifer-crops-in-organic-farming-systems

Poinsettia: Some Common Diseases of the Christmas Flower

2011-12-16T10:41:00.001-05:00

Fig. 1. Poinsettia- the Christmas flower
(with permission Benson, et al. 2002. Plant Health Progress
doi:10.1094/PHP-2002-0212-01-RV).

Poinsettia, the Christmas flower, (Fig. 1) was introduced to the United States from Mexico in 1825 by the first U.S. Ambassador to that country, Joel Roberts Poinsett of Greenville, South Carolina (Fig. 2).

Fig. 2. Joel Roberts Poinsett, first US Ambassador to Mexico
(with permission Benson, et al. 2002. Plant Health
Progress doi:10.1094/PHP-2002-0212-01-RV).

Commercial interest in poinsettia as a potted plant grown in the greenhouse did not get much attention until the 1950s and 60s, when breeding programs developed plants with stiffer stems, multiple shoots at each pinch point, larger flower bracts, and better keeping qualities. Today, poinsettias come in a variety of forms and bract colors. The value of poinsettias is about $145 million per year in the United States with about $17 million coming from North Carolina growers (Fig. 3). Although poinsettias are the Christmas flower, it is only consumer preference that limits year round sale.

Fig. 3. Poinsettias in commercial production
as the flower bracts are beginning to turn red.

Poinsettias are propagated vegetatively by cuttings taken from stock plants usually beginning in late June and early July just when greenhouse temperatures are highest. Cuttings are propagated typically in either polyfoam wedges, rockwool, or direct stuck in the finish size pot. Regardless of propagation strategy, cuttings must be misted several times a day to keep them from wilting until roots form on the stem of the cutting (Fig. 4).

Fig. 4. Propagation of poinsettia cuttings in polyfoam rooting
wedges under an intermittent mist system.
Note droplets of water on foliage from misters.
(Photo E. Lookabaugh)

During propagation, growers must avoid or prevent a number of plant diseases that can attack the cuttings. Under extreme moisture conditions, the soft rot bacterium, Erwinia carotovora attacks the cut end of the stem resulting in a mushy, watery rot that kills the cutting (Fig. 5).

Fig. 5. Erwinia soft rot has collapsed these poinsettia
cuttings in propagation
(with permission Benson, et al. 2002. Plant Health
Progress doi:10.1094/PHP-2002-0212-01-RV).

Even when misting systems are functioning normally, Rhizoctonia stem rot caused by R. solani can cause a canker on the lower stem that kills the cutting (Fig. 6, 7). When cuttings are stuck directly in potting mix in the finish pot, Pythium rot caused by several species of Pythium as well as Rhizoctonia stem rot can develop, if these pathogens are introduced by faulty sanitation procedures. Healthy cuttings root in about 4 to 6 weeks depending on temperature, if plant diseases do not develop.

Fig. 6. Poinsettia cutting in a polyfoam propagation
strip with Rhizoctonia stem rot. Note brown stem
lesion at bottom of cutting near foam surface. (Photo Mike Benson)

Fig. 7. Rhizoctonia stem rot. Two close ups of a stem lesion with
the white mycelium of the Rhizoctonia pathogen present
(with permission Benson, et al. 2002. Plant Health
Progress doi:10.1094/PHP-2002-0212-01-RV).

Cuttings once rooted in polyfoam wedges or rockwool must be transplanted to a soilless potting mix in a pot to finish for retail. The most important foliar disease growers must guard against in this stage of production is gray mold caused by Botrytis cinerea.(Fig 8). As the plant canopy grows and fills in, high humidity in the microclimate of the canopy is an ideal environment for gray mold. Growers must ventilate greenhouses properly to avoid high humidity and some even use bottom heat via air tubes under the greenhouse bench to help dry out the plant canopy. Fungicide sprays may also be used to prevent gray mold.

Fig. 8. Botrytis blight on foliage. Note dead tissue and abundant
‘gray mold’ sporulation on the infected tissues. This infection developed
inside the plant canopy where humidity was high favoring
pathogen infection and sporulation. (photo Mike Benson)

In the 1990s powdery mildew caused by Oidium spp. caused severe losses for many growers. The disease was particularly devastating because it often times did not develop until the plants already had color in the flower bract and by that time the grower had most of the expense of growing the crop already invested in it (Fig. 9). Growers also were reluctant to use fungicides sprays for powdery mildew control in the late stages of production because of spray residue concerns on the flower bracts. The disease has not been a problem in the last decade, however, due to changing cultivars and better management practices.

Fig. 9. Colonies of powdery mildew on leaves (left) and flower bracts (right)
(with permission Benson, et al. 2002. Plant Health Progress doi:10.1094/PHP-2002-0212-01-RV).

Scab is a stem and foliage disease caused by the fungus Sphaceloma poinsettiae that can occur periodically, resulting in unsalable plants. The most striking symptom of scab is the extra long stems produced by plants infected with this fungus (Fig. 10). Leaf spots also develop on infected plants. Outbreaks of scab usually occur when the pathogen is introduced with poinsettia stock material arriving from Central and South America where the fungus occurs throughout the year.

Fig. 10. Abnormally elongated stems of poinsettia due to scab disease
(with permission Benson, et al. 2002. Plant Health Progress doi:10.1094/PHP-2002-0212-01-RV).

The most important root disease affecting poinsettia is Pythium root rot caused by several species of Pythium the most common being P. aphanidermatum, but P. irregulare, P. cryptoirregulare and P. ultimum also cause loss. The fungus-like Pythium survives between crops in infected plant material from previous crops whether they are poinsettia or not. Without thorough sanitation between crops Pythium can be re-introduced to the new poinsettia crop by infested crop debris or through the irrigation system. The most common symptom of Pythium root rot is stunting of the plant as it fails to keep pace with the growth of healthy plants (Fig. 11).

Fig. 11. Stunting of poinsettia plants caused by Pythium root rot during finishing.
Note healthy plant in foreground compared to stunted, disease plants scattered throughout.
(Photo Mike Benson)

Under severe disease pressure, the foliage of plants with Pythium root rot develops wilt symptoms and does not recover with irrigation. Affected roots are discolored (Fig. 12). This disease can attack the crop at any time from propagation through finishing. Pythium root rot occurs in greenhouses regardless of location as some Pythium species are aggressive at low temperatures and others at high temperatures. Overwatering favors Pythium root rot. Fungicide drenches are commonly used to prevent the disease.

Fig. 12. Pythium root rot of poinsettia on a newly-transplanted rooted cutting.
Wilt symptoms (left) and close up of discolored roots with root rot from same plant (right).
(Photo Mike Benson)

Phytophthora root rot caused by P. drechsleri and P. nicotianae also can attack poinsettia during the finishing stage resulting in unsalable plants. Phytophthora is fungal-like pathogen similar to Pythium. Symptoms are the same, as well. Unlike Pythium, however, these Phytophthora pathogens can also splash onto poinsettia foliage causing a blight disease. Like Pythium root rot, overwatering favors this disease too and fungicides are commonly used to prevent the disease.

For a detailed history of the poinsettia and poinsettia diseases click here

Post prepared by Mike Benson

Sample of the Week: Girdling on Arizona Cypress

2011-12-12T14:13:00.000-05:00

Notice constricted base (Photo: Jennifer Pries)

This week we received an Arizona cypress that had died back rapidly in the fall. Nearby trees were unaffected and the client suspected that the lower stem might have been damaged by voles. However, Dr. Hodges, our tree diagnostician, found constriction at the lower stem (trunk) but could not find evidence of vole damage. Upon further examination, Dr. Hodges concluded that a root had grown around the base of the stem, girdling the tree. Root girdling occurs when the roots of the plant grow around the base or main stem of the tree causing restricted water and nutrient movement. Growth slows down, leaf production decreases and eventually, the tree will begin to die back.

Notice roots curling around base (Photo: Jennifer Pries)

Planting trees too deep or mulching too high around the tree can promote root growth around the base of the tree. Trees grown in container nurseries are more prone to root girdling because the roots are forced to grow in a circular fashion in the pots. Proper pruning of the roots in the nursery and before transplanting can significantly reduce the potential for root girdling in future.

For more information on proper transplating, click here
For more information on root girdling, click here

Edema

2011-12-02T10:44:00.001-05:00

This week’s sample consisted of several detached leaves from a spathe flower plant. Symptoms consisted of chlorotic blotches and some darker flecking on the leaves. One leaf was completely brown but not decayed. The symptoms were not suggestive of a foliar disease, and no fungi were observed on the spots. As a precaution, some leaf pieces were incubated, but nothing grew out.

Edema on spathe flower (Photo: Mike Munster)

Under the microscope, there were small, slightly raised bumps on the leaves. Mike Munster, the diagnostician who worked with the sample, suspected edema. Edema is a common abiotic disorder that occurs on many herbaceous and woody plants. Edema can be a problem on greenhouse crops and on plants grown outdoors. The most obvious symptoms include the formation of tiny blisters, warts, or raised bumps on the undersurface of leaves. With age, these bumps may become reddish brown and can be mistaken for rust pustules.

Notice red pustules on underside of leaf (Photo: Mike Munster)

Edema on geranium (Photo: Mike Munster)

Typically, edema is a problem in cool, wet conditions when the soil water is warmer than the atmosphere. Edema occurs when the roots take up more water than is lost through transpiration, resulting in accumulation of water in intercellular spaces. Excess water accumulates in the leaf causing leaf cells enlarge and block the stomatal openings. These enlarged inner cells cause the epidermis to rupture and become crusty with age.

Crusty edema on tomato (Photo: Frank Louws)

Crusty edema on tomato (Photo: PDIC Database)

For control:

Avoid irrigating during cool, humid, cloudy weather.

Reduce humidity in greenhouses by venting and increasing heat, improving air circulation, increasing light intensity, spacing plants further apart.

Avoid standing water under pots

Edema on swiss chard, notice the blackened stomata (Photo: Mike Munster)

Edema on lilac, similar to fungal leaf spots (Photo: Mike Munster)

For more information, click here

Phytophthora Root Rot on Fraser Fir

2011-11-29T09:54:00.002-05:00

Fraser Fir: The "Cadillac" of Christmas Trees

Fraser fir is a highly desirable Christmas tree species grown in the mountains of Western North Carolina and elsewhere across the United States. As a leading producer of Christmas trees, North Carolina growers must overcome weeds, insects, and disease to produce that beautiful tree you buy on the Christmas tree lot.

Fraser fir nursery bed where seedlings are grown up to

5 years before transplanting to the field. (Photo: Mike Benson)

Typical Fraser fir planting in Western North Carolina

after about 5 to 6 years in the field. (Photo: Mike Benson)

Although growers have good management tools for weeds and insect pests, Phytophthora (pronounced fy-TOF-thor-uh) root rot threatens long-term production of Fraser fir. The pathogen, Phytophthora, produces zoospores that can swim to tree roots in saturated soil or run-off. Throughout the 11 to 15 years or more that is takes to produce a 6 to 8 foot tall Fraser fir, Phytophthora root rot is always a threat.

Fraser fir planting that experienced Phytophthora root rot that started on trees at top of

ridge. Over several years, trees downhill from ridge became infected and died.

The Phytophthora pathogen produces spores that are carried in water run-off, so

the ‘wedge’ shaped area of missing trees developed in the downslope drainage

area of the field as trees were killed by the disease. (Photo: Mike Benson)

Fraser fir planting after about 6 years in the field. Note patch of trees killed by

Phytophthora root rot in far edge of field. (Photo: Mike Benson)

Lower branch ‘flagging’ may be the first indication that a Fraser fir has Phytophthora root rot. Once the Phytophthora pathogen has infected enough of the root system that the plant can no longer transport water and nutrients adequately, the foliage becomes yellow then turns reddish brown a short time later. The tree will eventually die from the disease.

Lower Branch "Flagging" (Photo: Mike Benson)

Root systems from a healthy Fraser fir transplant (right) compared to an infected

and dying transplant (left). Roots killed by the Phytophthora root rot pathogen

are dark, reddish brown in comparison to root tips on healthy plants that are white.

(Photo: Mike Benson)

Growers manage the disease by planting healthy fir transplants into fields that are well drained. Once disease develops in a tree, however, that tree is lost. Future production in that area of the field is also threatened because the pathogen survives many years in soil.

In the future, forest tree breeders and plant pathologists hope to develop a Phytophthora resistant fir with qualities equal to the Fraser fir. So when you buy that fresh cut Christmas tree this year, just remember that the Christmas tree grower was able to overcome a lot of potential problems to provide that tree for you.

For more information, click here

Special thanks to Mike Benson for writing this post!

Sample of the Week: Papaya Ringspot Virus on Watermelon

2011-11-18T12:27:00.000-05:00

Recently, we received a very interesting watermelon sample that was infected with Papaya Ringspot Virus (PRSV). This is only the second time we have seen this disease in the clinic. PRSV causes diseases on cucurbits and papaya plants worldwide. The most obvious symptom of PRSV infection is the formation of sunken ring spots on the fruit. These spots are very diagnostic of the disease. Other symptoms include mosaic or mottling of the leaves and oily streaks on the stems and petioles. In some cases, the leaves may be severely narrowed, which gives them a “shoestring” like appearance.

Rinspot symptoms of PRSV (Photo by: Jennifer Pries)

PRSV is a member of the potyvirus group of viruses and is transmitted by aphids. The virus is vectored in a nonpersistant manner, meaning it does not replicate in the aphid vector. Aphids feed on infected plants, and within seconds or minutes they hop to healthy plants and transmit the virus as they feed. The virus can spread very quickly through fields.

The two major strains of PRSV are PRSV-W and PRSV-P. PRSV-W (the watermelon-infecting type) used to be known as Watermelon Mosaic Virus I, and can only infect cucurbits. PRSV-W is the major strain found in the Southeastern US, but it is also present in tropical areas where PRSV-P is present. PRSV-P (the papaya-infecting type) is only found in tropical and subtropical areas were papayas are grown, but PRSV-P can also infect cucurbits. Controlling this disease is somewhat difficult, especially in papaya. Genetic resistance to PRSV is available in some commercial varieties of cucurbits and is the most effective way of controlling the disease. Unfortunately, resistance has not been found in watermelon. Aphid control is not practical because of the nonpersistant manner in which the virus is transmitted.

For more information,

http://www.apsnet.org/edcenter/intropp/lessons/viruses/Pages/PapayaRingspotvirus.aspx

http://www.extento.hawaii.edu/kbase/crop/type/papring.htm

For resistant varieties,

http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm

Sample of the Week Sweetpotato Scurf

2011-11-11T08:22:00.001-05:00

With Thanksgiving on the way, we decided to highlight a common disease of sweetpotatoes, but don’t worry, it wont affect the taste of your sweetpotato casserole! Scurf is caused by the fungus Monilochaetes infuscans. The fungus only grows in the sweetpotato skin and produces spores on the surface of the skin. As shown in the photos, the dark splotches on the skin are areas infected with the fungus. The fungus does not penetrate below the skin, so the sweetpotatoes are still edible, but because of the dark discoloration that results, diseased sweetpotatoes have lower market values.

Healthy sweetpotatoes are infected by spores present in the soil. The disease can also spread through contaminated crates, baskets, and storage houses. The fungus does not attack the above-ground portion of sweetpotato plants, and does not attack other hosts so rotation is an effective way to prevent scurf problems. Scurf is usually worse during rainy seasons.

For more information and control recommendations, click here

Sample of the Week: Cucurbit Downy Mildew on Greenhouse Cucumbers

2011-11-04T13:23:00.000-04:00

This week’s sample is cucurbit downy mildew on greenhouse cucumber. Cucurbit downy mildew affects all members of the cucurbit family: watermelons, cantaloupes, squash, pumpkins, and cucumbers. Disease is favored by long periods of high humidity and mild temperatures, which unfortunately, describes most nights in the Southeast during the production season and in greenhouses year round. Downy mildew occurs every year in North Carolina, and in recent years has become increasingly destructive on cucumber.

Greenhouse Symptoms (Photo: PDIC Database)

The most obvious symptoms of downy mildew are small angular spots on the foliage, with older leaves generally being infected first. “Angular leaf spots” describe a type of symptom where the spots are defined by the boundaries of leaf veins, so that the shape of the spots is angular rather than round or blotchy. Downy mildew spots appear pale green to yellow as first, eventually becoming brown and necrotic with age.

Angular Leaf Spots (Photo: PDIC Database)

During humid conditions, brown to purplish fuzzy growth can be observed on the underside of the foliage. This downy growth is actually sporulation of the pathogen.

Fuzzy Sporulation (Photo: Shawn Butler)

Dichotomously branched sporangiophores with lemon-shaped sporangia are visible when view through a microscope. As infection progresses, leaves will eventually turn brown and curl upwards. The leaves are the only part of the plant affected. Downy mildew infections result in yield loss and misshapen fruits. Damage from foliar infections also increases sunlight exposure on fruit and leads to sunscald.

Cucurbit downy mildew is caused by Pseudoperonospora cubensis. P. cubensis belongs to a group of fungus-like organisms called oomycetes (or water molds). This group is also home to other aggressive plant pathogens including Phytophthora and Pythium. P. cubensis is an obligate parasite, meaning it requires living host tissue to survive and reproduce. North Carolina winter temperatures are too cold for the pathogen to overwinter, so it dies out every winter. Unfortunately, Southern Florida has the perfect combination of mild winters and wild cucurbit plants. The pathogen survives all year in Florida and inoculum builds up on wild plants. Spores are windblown and can travel long distances on air currents. Summer weather events, like hurricanes, act as the perfect mode of transportation. Like birds, downy mildew spores fly north for the summer and end up on our cucurbits! In this particular situation, the greenhouse plants probably became infected as spores from nearby field cucumbers blew into the greenhouse over the summer.

For more information on this disease, click here

For more information on controlling this disease, click here

For more information on forecasting this disease, click here

Sample of the Week: Botrytis Blight of Pansy

2011-10-28T11:46:00.000-04:00

Botrytis Blight on Pansy (Photo: Mike Munster)

This week we received pansies from raised beds in a trial garden in Henderson County, North Carolina. The roots and crowns were in good condition but some of the flowers, flower stalks and leaves were decaying. The main symptom on leaves was a very watery rot. The fungus Botrytis cinerea was observed sporulating on some of the material when we received the sample. Sporulation was heavy after a day of moist-chamber incubation, as indicated by distinctive masses of gray spores. Making a diagnosis when Botrytis is involved can be tricky, because the fungus can be both a secondary invader and a primary pathogen. It often infects spent blooms and then moves into other parts of the plant. In this case it appears to be fairly aggressive, so Botrytis blight is the diagnosis.

Wet rot of pansy leaves caused by Botrytis (Photo: Mike Munster)

Stereomicroscope view of pansy flower stalk with sporulation from Botrytis cinerea
(Photo: Mike Munster)

For more information on Botrytis Blight, click here
Thanks to Mike Munster for this "Sample of the Week" submission.

Household Molds: What Hurricane Irene Left Behind

2011-10-27T15:29:00.000-04:00

Written by: Dr. Charles Hodges

A September 10, 2011 headline in the Raleigh News and Observer read “Irene leaves Aurora sodden in mold, misery”. Similar headlines were probably common in other newspapers and on radio and television as Hurricane Irene took her heavy rains northward, resulting in flooded homes and businesses - and heavy mold development - in her wake.

Mold development is a common occurrence whenever flooding occurs. However, it does not take hurricanes and flooding to cause mold development in homes and other buildings. Mold can develop anywhere there is adequate moisture and a suitable substrate on which to grow.

Water from leaks in the roof and from broken pipes is the most common and serious cause of mold in buildings. However, there are several other sources of moisture in homes that can result in the occurrence of mold. Some of these include crawl spaces where the soil has become wet, poorly ventilated bathrooms, kitchens where steam from cooking condenses on the cabinets or walls, small closets in which are placed wet clothes or shoes, window sills wet by water that condensed on the inside of window panes, and condensation of moisture within HVAC ducts and on metal vents during the summer when the air conditioning is on.

Two mold samples received in the Plant Disease and Insect Clinic during the winter came from old houses that did not have wall insulation. The houses were occupied by elderly residents who kept the temperature very high, causing water to condense on the inside walls and leading to very heavy mold development.

Mold inside wall (Photo: PDIC Database)

Molds belong to a group of organisms called fungi. There are many thousands of different kinds of fungi. Some of these cause diseases of plants and animals, some are responsible for the decomposition of dead organic matter, and others are important in fermentation processes or in the production of antibiotics. The basic vegetative phase of molds (threads called hyphae), and the reproductive phase (spores), are microscopic. When large colonies of mold develop and produce spores, however, they are often visible to the naked eye. The colonies can be of many different colors – white, black, blue, green, pink, or brown - depending on the individual mold species that produce them.

Variety of household molds (Photo: PDIC Database)

Most molds are spread primarily as spores that move through the air on even the most gentle of air currents. Upon landing on a suitable substrate, and with enough moisture, spores germinate and form a colony. The rate of development of the colony depends on the individual mold species, the substrate, and temperature and moisture conditions. Many of the most common household molds prefer substrates containing cellulose; e.g., the cardboard covering of sheetrock, ceiling tiles, wood, paper, and fabrics. Dead leaves of ornamental plants are a common source of mold spores in buildings. The leaves fall from the plant into the container where they are wet when the plant is watered, often resulting in heavy spore production. In the outdoors, mold spores are formed in large numbers on all types of dead organic material, are spread through the air, and often enter homes through open doors or windows. These are often the same species of molds that are found indoors.

Mold on wood wall (Photo: PDIC Database)

Molds can and do cause various kinds of damage in buildings, but for the most part the damage is cosmetic, such as stains on walls, floors, ceilings and furnishings.

Heavy mold on wall (Photo: PDIC Database)

Molds also can produce unpleasant odors. Most mold fungi are unable to decompose wood, thus do not cause structural damage. Any structural damage in buildings where mold is present usually is caused by water per se rather than molds. At times, the presence of surface molds can indicate that wood decay fungi are also present. These fungi are capable of decomposing wood and, like mold fungi, are active at high levels of moisture. Often there is no visual evidence of wood decay fungi on the surface of the wood, but the presence of surface molds indicates conditions that could lead to damage by wood decay fungi.

White mold on window sill (Photo: PDIC Database)

Most people are concerned about the health risks associated with household molds, and in some cases these concerns are valid. Many people have allergenic reactions such as headache, sneezing, runny nose, skin rash, etc. to high concentrations of certain mold spores. Other individuals can be in the same room at the same time and have no reaction. Some mold fungi produce toxic compounds and exposure to these can pose more serious health hazards, especially in individuals that have a compromised immune system such as from radiation treatment or chemotherapy. Unfortunately there have been numerous reports in the media about the danger to human health from the so-called black toxic mold Stachybotrys chartarum, especially in buildings that have been flooded. More recent research has shown that this fungus is not nearly as dangerous as once reported.

Mold on windowsill (Photo: PDIC Database)

Most mold problems in homes can be detected visually when the colonies develop on walls, ceilings and floors. However, molds can develop in other areas where they may not be easily seen, such within walls, attics, crawl spaces, within HVAC ducts, or inside cabinets, especially cabinets under sinks where water leaks often occur. The pile of carpets made with artificial fibers is usually resistant to mold growth; however, the backing of most of these carpets support mold growth if sufficient moisture is present. One should automatically assume that when water leaks occur, there is an excellent chance of mold development until the water problem is corrected and the wetted material has dried out.


Mold on wooden chair. This chair was packed for shipping before it dried completely, resulting in mold development in transport. (Photo: PDIC Database)

The identification of household mold fungi, especially to the level of species, is often difficult and time consuming. One method of sampling mold spores in buildings uses an air sampler that draws air over a microscope slide coated with a sticky substance onto which the spores adhere. The slide is then examined under the microscope and the spores identified, usually to the level of genus or groups of genera. It is not possible to identify the spores to the level of species using this method. This is understandable when one considers that the genera Aspergillus and Penicillium, some species of which are common household molds, each contain more that 200 known species. This method does, however, give a relative measure of the number of spores in the air at the time of sampling.

Colony of Penicillium (Photo: PDIC Database)

Another method uses culture plates containing a general purpose growth medium that can be purchased at stores such as Lowes or Home Depot or your local hardware store. The lid from the plate is removed and the bottom containing the medium is placed on the floor. Plates are usually placed in different rooms in the house, and in the attic and crawl space. Since the spores fall onto the plates by gravity, it is helpful to do the sampling when very little activity is going on in the house and the ventilation fan is off. After a prescribed period of time, perhaps one hour, the lids are replaced and the plates are left at room temperature for several days.

Culture plate submitted by homeowner (Photo: PDIC Database)

At this time the mold colonies are beginning to develop, usually one colony develops from one spore. The molds on the plate can be identified by sending the plates to private laboratories as indicated by the instructions in the package.

The Plant Disease and Insect Clinic also provides mold identification services. To submit a sample, collect mold by swiping a clean cotton swab through the colony, and immediately placing the swab in a clean plastic bag and sealing it. A separate sample should be taken for each type of mold colony seen in each room or from different rooms. Submit the samples to the Plant Disease and Insect Clinic, where they will be cultured on growth media. Identification will be made at least to the level of genus and to the level of species for the more common molds. This method gives only a relative indication on how much mold is present. We also accept culture plates collected as described above.


Several mold/ yeast varieties identified by the PDIC. Culture plates were streaked with a cotton swab and sealed. After several days, the diagnostician examines the colony types for identification. (Photo: PDIC Database)

Most mold can be removed by wiping the moldy area with a cloth wet in a ten percent solution of common household bleach. Finished surfaces or fabrics should be tested to see if the bleach will harm the surface. If the mold growth is heavy, a face mask should be worn while cleaning. Household bleaches have little residual activity, and it may be necessary to clean again until the substrate is too dry to support mold growth. If the mold is covering a large area which requires removal of water-damaged floor, walls or ceiling, the room should be sealed by closing the door or sealing the opening with plastic while the renovation is being done so that the spores do not spread to the rest of the house. There are a large number of private mold remediation companies, which can safely remove mold from buildings.

Mold growing on a fabric cap (Photo: PDIC Database)

The most important thing that the public can do about molds is to prevent water problems or quickly correct them when they are found.

Black Root Rot in the Landscape

2011-10-18T13:59:00.001-04:00

Written by: Emma Lookabaugh and Dr. Barbara Shew

Root rot is one of the most commonly diagnosed disease problems of woody landscape ornamentals in North Carolina. Every year we receive boxwoods, Japanese hollies, rhododendrons, azaleas, camellias and other woody shrubs and trees that have one of the “big three” root rot diseases: Phytophthora root rot, Thielaviopsis black root rot, or Armillaria root rot. Earlier, we discussed Armillaria root rot. With fall landscaping season in full swing, now is a great time to focus on black root rot.

Black root rot affects many plants, including woody ornamentals, annuals, and even field crops. It is the number one disease we see on Japanese hollies. Black root rot also is an important disease in pansy, annual vinca (Madagascar Periwinkle), and other bedding plants.

In the landscape, symptoms of black root rot on Japanese hollies include stunting and lack of plant vigor, yellowing of the foliage, and eventual leaf drop. The most obvious symptoms of this disease are black lesions that occur on the tips of feeder roots, hence the name black root rot. These lesions expand as the pathogen colonizes the root tissue, and plants decline as the root rot advances. Young holly plants in the nursery can be killed within a few weeks from severe infections, whereas mature plants decline more slowly.

Stunting symptoms associated with BRR in the landscape
(Photo: Charles Hodges)

BRR Symptoms: Notice the black root tips
(Photo: Plant Path Departmental Slide Collection)

On pansy, symptoms include yellowing of new growth, stunting, and root rot. If you rinse away the soil and examine the roots, black root rot will appear as small black lesions that are found along the length of the root. The lesions are microscopic at first, but later will become visible as the lesions expand. In more advanced cases, the entire root system is blackened and eventually rots away.

Stunting Symptoms of BRR on Pansy
(Photo: Mike Munster)

Root rot and stunting symptoms of BRR:
Look closely at the roots on the left and you can see black lesions on the stem
(Photo: Mike Munster)

Black root rot is a caused by the fungus Thielaviopsis basicola. This fungus is a common inhabitant of many soils in the US. It can easily be distinguished by its characteristic chlamydospores, which are black and barrel-shaped. These are the primary survival structures of the pathogen. In addition, Thielaviopsis basicola produces abundant conidia in infected root tissues. Both spore types are spread in soil water or in infested soil or root fragments.

Dark chlamydospores and clear conidia of Thielaviopsis basicola
(Photo: H.D. Shew)

Chlamydospores inside pansy root tissue
(Photo: Mike Munster)

Infected plant material from the nursery and infested soil in the landscape are the most common sources of infection in Japanese hollies. In the greenhouse, Thielaviopsis basicola may enter on infected cuttings or other diseased plant material. It may also be present in infested potting medium or on contaminated pots or trays. Previously infected transplants, growing media, or garden soil are common sources of infection for pansies and other bedding plants in landscapes.

Example of potential source of inoculum:
Notice the dirty pots and cull pile right next to "healthy" plants
(Photo: Emma Lookabaugh)

Cultural practices are the main means of black root rot control. In landscapes with a history of black root rot, plant resistant holly varieties or other plants that are not susceptible to black root rot. Infected Japanese hollies should be removed and these susceptible species should not be replanted in the same location. American and Yaupon holly are moderately resistant, while English and Chinese hollies are highly resistant to black root rot. Many woody ornamentals used in NC landscapes, including boxwoods, azaleas, and rhododendrons are not susceptible to the fungus, providing many options when replacing diseased plants.

Check pansies and other bedding plants before you buy them. Choose plants with white, healthy root systems that have colonized the entire plug or pot. Avoid transplants with black or rotted roots. Resist the temptation to plant beds of pansies while the weather is hot. Wait a few weeks for lower temperatures, which will reduce stress on new transplants and help the plant resist infection.

Sanitation is the most important defense against black root rot in greenhouse/nursery production. Infected plants should be removed and destroyed. Use only disease-free cuttings and propagation material. Proper sanitation of trays and benches is crucial in managing this disease. For more information on cultural practices see Cultural Control Practices Guide. For more information on chemical sanitation see Sanitation Table.

Poor sanitation practices:
Notice the standing water and stack of diseased/discarded plants and pots next to healthy plants
(Photo: Emma Lookabaugh)

Fungicide drenches with thiophanate-methyl can be helpful if applied preventatively. See the NC Ag Chemicals Manual (http://ipm.ncsu.edu/agchem/agchem.html) for more information. Fungicides will not “cure” infections that are well-established, so it best to use them preventatively.

For more information:

http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/od7.htm

Special Thanks to Dr. Kelly Ivors for helping with this post!

Sooty Blotch and Flyspeck of Apples

2011-09-29T10:49:00.001-04:00

Sooty Blotch and Flyspeck (Photo: Bugwood)

With fall coming fast, it’s time to gear up for apple season. Before you make your trip to the local farmer’s market, we decided to introduce you to the two most common apple diseases in North Carolina, sooty blotch and flyspeck. Without the use of fungicides, these two diseases would affect virtually all apples grown in the southeastern United States. These diseases are found on all cultivars of apples and both diseases can be found on the same apple at the same time.

The most common symptom associated with sooty blotch is the growth of feathery, olive green fungal colonies on the surface of mature fruit. Flyspeck can be recognized by the presence of very small, shiny, black, dots arranged in an irregular or circular pattern on the fruit surface. This gives fruit the unappetizing appearance of being covered with fly droppings.


Sooty Blotch and Flyspeck (Photo: Bugwood)

Both of these diseases cause only superficial damage on the apple surface. The fungi that cause them, grow on the surface of the cuticle and do not damage the apple itself or affect its flavor or quality. Sooty blotch and flyspeck cause losses in commercial apple production because affected fruit are downgraded from valuable fresh market grades to much cheaper processing or juice grades.

Sooty Blotch and Flyspeck (Photo: PDIC Database)

Over 60 putative species of fungi have been associated with sooty blotch and flyspeck worldwide. In the Southeast, Peltaster fructicola, Leptodontidum elaitus, Stomiopeltis spp. and Geastrumia polystigmatis are the most common species associated with sooty blotch and Schizothyrium pomi is the most common species associated with flyspeck. Fungi that cause sooty blotch survive the winter on apple twigs and reservoir hosts surrounding the orchard. Spores are dispersed by wind and windblown rainwater to developing fruit in the spring and early summer. Secondary spread occurs throughout the summer. Usually, symptoms can be seen 20 to 25 days after infection.

S. pomi also overwinters on apple twigs and other perennial reservoir hosts. Airborne ascospores are the primary means of infection and are usually produced for about 2 months beginning around bloom. Specks, which are actually fruiting bodies of the fungus, appear about 3 to 6 weeks after infection. Secondary spread occurs through windblown conidia produced on infected fruit and twigs and on reservoir hosts surrounding the orchard.

Sooty Blotch (Photo: PDIC Database)

Commercial growers control these diseases with cultural practices and fungicide applications. Cultural control practices include pruning during dormant and summer seasons and fruit thinning. Pruning and fruit thinning reduce the drying time within the canopy and allow better fungicide penetration through the canopy. Sooty blotch and flyspeck fungi require wetness to infect. Pruning and fruit thinning discourages these fungi by increasing airflow through the canopy. Mowing weeds and grasses under apple trees also helps trees stay dry. Another important cultural practice is removal of surrounding reservoir hosts, especially brambles. Surrounding blackberry plants act as harbors where these fungi are able to multiply during the season and then spread to nearby apple fruit.

In addition to cultural practices, these diseases are controlled with preventative fungicide applications. Preventative sprays need to be applied beginning about second cover (about a month after bloom) and continuing at 10 – 14- day intervals until harvest.

Since sooty blotch and flyspeck are harmless to people and apples, there is no reason to apply fungicides to control them at home – nor do you need to avoid buying apples with sooty blotch and flyspeck, especially for cooking or baking. Most of the fungal colonies can be removed by washing the apples in a mild solution of bleach.

For more information:
Apple Disease Factsheet

A Growers Guide to Apple Insects and Disease of the Southeast

Special thanks to Dr. Turner Sutton for helping with this post!

Sooty Mold: Ugly... but Mostly Harmless

2011-09-20T12:06:00.000-04:00

Have you ever noticed that some of your shrubs have a black mold coating their leaves? Recently, I was at home visiting my parents and my mom was telling me that her crape myrtle was covered in some sort of black mold. She was very concerned and wanted me to go “check it out.” I took one look at the bush and knew we were dealing with sooty mold.

Sooty Mold on Crape Myrtle (Photo By: B. Lookabaugh)

Sooty molds are dark-colored, nonparasitic fungi that grow on insect honeydew. So what is honeydew - sounds tasty doesn’t it? It is a sweet, sticky liquid produced by aphids, soft scales, mealy bugs, and some species of leaf hoppers. These insects suck sugary sap from the leaves and excrete honeydew - a mixture of sugars, amino acids, and other organic substances. Essentially, honeydew is aphid poop!

Soon after a plant is heavily infested with aphids or other sucking insects, leaves are covered in honeydew. The honeydew serves as a nutritional substrate for dark-walled sooty mold fungi. In severe cases, honeydew can drip from infested leaves and stick onto other plants or objects. When this happens, you might end up with sooty mold on your car, house, propane tank, or patio furniture!

Sooty mold growing on sign beneath infested tree
(Photo By: Whitney Cranshaw, Bugwood)

Like my parents, you may notice more sooty mold problems after it rains. Rain can deposit honeydew even on plants that are not infested with honeydew-producing insects. Since spores of sooty mold fungi are also dispersed in wind and rain, sooty mold problems soon follow.

Sooty molds typically grow in patches on plant surfaces and can be distinguished from other fungi because they are strictly superficial. The dark mycelium can be wiped clean from the plant surface using a moistened paper towel or your hand. Most sooty mold fungi are harmless to plants. If the mold is extremely abundant, it can prevent leaves from obtaining adequate sunlight and thus reduce plant vigor. Sooty molds also lessen the aesthetic value of ornamental plants and shrubs.

Even if sooty mold is extensive, it is best not to apply fungicides. The mold can be washed away with a forceful jet of water. You can control the insects that produce the honeydew on which the sooty mold grows with insecticidal soap or horticultural oils. Horticultural oils also loosen the sooty molds from the plant surface, which speeds up the weathering away process.

Aphids: Responsible for producing honeydew
(Photo By: B. Lookabaugh

Some plant species and varieties are more prone to aphid problems and thus sooty molds than others. For example, some varieties of crape myrtle are not prone to aphid and sooty mold problems whereas others are very likely to be infested. See Crape Myrtle Diseases & Insect Pests from Clemson University for more information about sooty molds and a list of recommended varieties.

For more information:

http://www.ces.ncsu.edu/depts/ent/notes/O&T/houseplants/note41/note41.html

http://www.na.fs.fed.us/spfo/pubs/howtos/ht_sooty/ht_sooty.htm

Rainy Day Weekend Activities

2011-09-16T14:30:00.000-04:00

Need something exciting to do this weekend? Join the Plant Disease and Insect Clinic at BugFest and CALS Annual Tailgate. BugFest is an annual festival that celebrates all things creepy and crawly! This year, the theme is spiders! The festival is held at the North Carolina Museum of Science in downtown Raleigh. NCSU Department of Plant Pathology (with the Plant Pathology Society of North Carolina and USDA) will once again be featuring the BugBus exhibit. Grad students will be showcasing mites as plant pests and carriers of plant pathogens. Kids can come learn about spider mites, fig mosaic virus, rose rosette virus, nematodes, and mummy berry disease. We will have microscopes set up so kids can view these tiny mites in action. BugFest hours are from 9am to 7pm on Saturday, September 17th. There are plenty on indoor exhibits, along with lots of spidery themed things to do outside!

For more information on BugFest, click here.

In addition to BugFest, the Department of Plant Pathology will also be at CALS Tailgate. CALS Tailgate is an annual event for NC State Alumi. In addition to a great meal, attendees will get the opportunity to see what our College has to offer from academics, research and extension. The event is packed around fun events, like a silent auction, live band, departmental displays, children's games, and of course, lots of free stuff. The Department of Plant Pathology will have a display featuring the Plant Disease and Insect Clinic, Plant Propagation Unit, and Turfgrass Diagnostics. Head over to our booth to see what our department has been up to and learn about plant diseases.

After the tailgate, you can head over to watch the NCSU vs. South Alabama game for Military Appreciation Night. Mark Gottfried, the new men's basketball coach, will be showing his appreciation for our military by parachuting into the stadium!

For more information on CALS Tailgate, click here

Hopefully the cool rainy weather won't ruin your weekend! We hope to see you Saturday!

Lions, Tigers, and ORB SPIDERS, OH MY!

2011-09-13T15:49:00.001-04:00

With BugFest coming this weekend to Raleigh's Museum of Natural Sciences, we found it appropriate to have a short posting on spiders, specifically orb spiders. For those of you not familiar with BugFest, it is an annual festival that celebrates all things creepy and crawly! Each year, the festival has a different theme, with this year's theme being SPIDERS. David Stephan, the Plant Disease and Insect Clinic's resident entomologist, prepared the following post on orb spiders, a common group of spiders found throughout North Carolina.

Orb Spiders

Spiders are among the most maligned and misunderstood creatures on Earth. These fascinating arthropods are mostly beneficial to humans as predators of insects and other pests, but the few that are genuinely dangerous to us have given all spiders a bad rap. Almost all spiders are venomous (except for the species in one obscure family), and almost all are predators. Very few species are truly aggressive, most opting to freeze or flee in encounters with people. All spiders produce silk, and many of them use this silk in various ways for prey capture, construction of retreats, courtship, protection of their eggs, etc.

Orb spiders of the family Araneidae are among our largest and most beautiful spiders (oh yes they are!). They spin those large, radially symmetrical webs that people often find in their yards from mid summer into fall. Outdoor lights and windows attract many insects, which makes them popular sites for orb spiders and others to spin their webs. The spider may wait in the center of its web, or in a hidden retreat nearby, ready to rush out and wrap prey that fly into the web. Most adults will die by winter, after preparing 1 or more sturdy egg cocoons. Orb spiders are timid and avoid contact with people, but blundering into one of their webs in the dark could give you a heart attack.

Golden Silk Orb Spider, Nephila clavipes
(Photoby David Hillquitst, Bogue Banks, NC)

Our largest NC orb spiders belong to the genera Araneus, Argiope, Neoscona and Nephila. The mostly tropical species of Nephila include the world’s largest orb spiders, and can build spectacular webs. The silk that spiders produce has amazing properties of tensile strength and extensibility, and scientists have been studying it for many years. Researchers in the College of Textiles here at NCSU have worked with orb spiders in the past. Currently, researchers in our Dept. of Chemical & Biomolecular Engineering are using the latest technology to study, duplicate and even improve on some of those properties of spider silk.

Golden Silk Orb Spider, Nephila clavipes
(Photoby David Hillquitst, Bogue Banks, NC)

Not enough spider info to satisfy your appetite? Be sure to visit BugFest, Saturday September 17th. NCSU Departments of Plant Pathology and Entomology have displays with even more info about spiders!

Additional Links:

BugFest

Golden Silk Spider

Special thanks to David Stephan for contributing this post!

Peanut Disease Control Following Hurricane Irene

2011-08-31T20:40:00.000-04:00

Written by: Dr. Barbara Shew, Peanut Extension Specialist

Sclerotinia blight

Heavy rain from Irene, wet vines, and the recent cool nights make ideal conditions for Sclerotinia blight. Today (Aug 31), all reporting weather stations in North Carolina are advising sprays and indicating high to very risk of Sclerotinia blight. Conditions will remain highly favorable for Sclerotinia blight for at least the next 5-7 days.

Make sure that fields with a history of Sclerotinia blight are protected. The last effective spray date for today is August 10. This accounts for 3 weeks of protection following a fungicide application. Fields that have not been sprayed since August 10 are not protected.

It is very important to catch Sclerotinia outbreaks when they first occur – this is the time when fungicides are most effective at controlling the disease. Scout carefully if you are in doubt about your field history or control efforts to date.

Even in fairly advanced cases, Sclerotinia blight can be hard to see unless you check plants thoroughly. Scout by checking 50 feet of row in several locations across a field. Part the rows and check inside the canopy for the fluffy growth of the Sclerotinia blight fungus on stems, leaves, and pegs. Infections may be present on leaves and stems that are not touching the ground, particularly after a heavy rain. Other signs and symptoms include bleached and shredded stems and black fungus structures (sclerotia) that look like mouse or insect droppings. Sclerotia often are found on or inside stems and pods.

Early development of Sclerotinia on stem

Stem shredding by Sclerotinia (Photo by Bridget Lassiter)

We are currently are working on yield loss models for Sclerotinia blight. While we have not finished our analysis, we have a rough idea of what to expect. Assuming a Sclerotinia-free yield of 4,600 lb/a, yield decreases about 50 lb/a for every 1% incidence (plants diseased) of Sclerotinia blight at 110 days after planting. This suggests that a reasonable treatment threshold at this point in the season is between 2-3% of plants diseased. If you expect a delayed harvest, I would definitely lean to the low end of this range (or even lower) so that you can maintain good control through the next several weeks.

Leaf spots and web blotch

Late leaf spot thrives when leaves are wet and night temperatures drop a bit. Late leaf spot is more difficult to control than early leaf spot. It will be very important to stay on top of late leaf spot control for the next couple of weeks - or longer if you expect a delayed harvest. Be particularly watchful on highly susceptible cultivars like Gregory and Perry.

We have seen little to no web blotch in the past several years, but outbreaks sometimes follow a tropical storm. Web blotch is recognized as large (½-inch) dark patches or blotches with faint or irregular margins. They are found only on the upper surface of the leaf at first. Young lesions have a grayish cast but later the blotches turn light brown. NC-V11 and VA 98R are highly susceptible to web blotch and most prone to outbreaks. A good leaf spot control program usually will control web blotch.

Web blotch

Headline will give excellent protection against late leaf spot and web blotch at 9 -12 oz/a. Most other foliar fungicides also perform well against these diseases. Avoid using tebuconazole since it is very weak against late leaf spot. Use a multi-site fungicide such as Bravo (chlorothalonil) for the last spray of the season. This will help to reduce the risk of developing pathogen populations that are resistant to other fungicides.

Rust

Peanut rust is rare in North Carolina, but sometimes shows up after a storm. Peanut rust is NOT the same rust that infects soybeans, but in some ways it is similar. Like soybean rust, peanut rust does not survive our winters. It is a sporadic problem in the southern-most peanut production areas of the US and is common in Central American and Caribbean countries. As with soybean rust, spores of peanut rust can be transported over long distances by hurricanes and other storms. Considering the path that Hurricane Irene took, it is possible that we will see scattered outbreaks of peanut rust.

Rust

Peanut rust produces numerous small reddish-brown pustules on the undersurface of the leaf. The pustules erupt to release millions of rust-red spores. These spores will stain a white cloth or paper that is swiped on the underside of a rusted leaf. Rust epidemics start in hot spots and spread quickly. Fungicides that are effective against rust include Bravo, Abound, and tebuconazole. Tilt (propiconazole) is not effective.

Corn Smut: Friend or Foe?

2011-08-26T13:30:00.000-04:00

Written by: Dr. Barbara Shew and Emma Lookabaugh

Sweet corn at the local farmers market
(Photo by: H.D. Shew)

On summer days, farmer’s markets are bursting with sweet corn. Shoppers buy ears by the dozens for good eating now and to stock their freezers for the winter. Corn – both field and sweet – is a relatively healthy crop and diseases usually do not trouble the home gardener. An exception is corn smut – it’s both common and easily recognized by its grotesque tumor-like galls and masses of dark sooty spores.

Recently, Dr. Mike Benson, a professor in our Department, brought in some smutted ears of sweet corn for class. The infected super sweet corn was his second planting during the first week of June. He noted that the fungus didn’t start showing up until the ears starting filling in during the first week of August and estimated that about 15% of his plants were infected in mid-August.

The corn smut fungus, Ustilago maydis, attacks corn (or maize; Zea mays) and its wild relatives (Zea spp.). It can infect all actively growing corn tissues, but the most obvious symptoms are tumor-like galls on the ears. Young galls are white and firm and are covered with a semi-glossy periderm, which eventually ruptures, exposing masses of sooty teliospores.

Young corn smut galls
(Photo: H.D. Shew)

The teliospores serve as overwintering inoculum for future corn crops. In the spring, teliospores are windblown or rain-splashed to nearby corn plants. The teliospores germinate to form sexual spores called basidiospores or sporidia. The sporidia can also be dispersed in wind or rain. Later, two sporidia fuse and give rise to the infective stage of the fungus.

Any above-ground plant part can be infected, including ears, tassels, silks, stalks, nodal shoots and leaf midribs. Distorted tissue may be noticeable within days after infection. Typically, galls form within a week and continue enlarging for up to three additional weeks. Initially, galls are composed primarily of host tissue undergoing tumor-like growth. As the galls age, their fleshy interior becomes streaked with black as dark sooty teliospores begin to replace the white host tissue. Eventually the gall becomes a mass of spores, dehydrates, and ruptures, releasing the teliospores.

Mature corn smut galls
(Photo: H.D. Shew)

Individual developing kernels are infected through the silks. Kernels are not susceptible to infection once pollination occurs, so any condition that reduces pollination favors smut infections. Drought stress (when pollen dies or tassels stop producing pollen) or extremely wet, humid weather (causing poor or no pollen production) opens up the window for infection. University of Illinois Professor Emeritus Jerald Pataky says that “wimpy males,” that is, plants that don’t produce pollen in adverse conditions or males (tassels) that are not ready when the females (ears) are ready for pollination, are more susceptible to smut.

Gall on single kernel
(Photo: H.D. Shew)

Smut usually makes sweet corn unmarketable due to cosmetic damage, but in parts of Mexico, it is actually prized. Traditional farmers gather young galls after natural infection and market them as Cuitlacoche (or Huitlacoche), a delicacy in Mexican cuisine. Often called the “Mexican truffle” or a “food of the gods,” it has been served up in Mexico since Aztec times. Nowadays, there is great interest in developing techniques for inoculating ears with smut and marketing the galls as gourmet fungi to upscale restaurants. It is a favorite ingredient in many soups, appetizers, and entrees because of its unique combination of earthy and corn flavors. Even here in Raleigh, NC, you can order up cuitlacoche and get a taste of this traditional Mexican delicacy.

Chicken breast stuffed with smut fungus
(Photo: B.B. Shew, Jibarra Restaurant)

In case you *don't* want smut in your corn, control options are limited. Rotation is somewhat helpful and it may help to remove and destroy (or eat!) smutted ears before the galls erupt. “Resistant” varieties are commonly recommended for control, but performance can be erratic since most are not truly resistant but instead escape infection. Choose varieties that are known to perform well in your region. Make several plantings during the spring. If all goes well, this will keep you in a steady supply of sweet corn for the summer. This also increases the chances that some of your plantings will escape major problems with poor pollination and smut.

Corn at the farmers market
(Photo: H.D.Shew)

References and links of interest:

Pataky, J. K., and K. M. Snetselaar. 2006. Common smut of corn. The Plant Health Instructor. DOI:10.1094/PHI-I-2006-0927-01

Jerald Pataky’s cuitlacoche recipes page http://www.sweetcorn.illinois.edu/Common-smut/Recipes.htm

In Mexico, Tar-Like Fungus Considered Delicacy

http://www.npr.org/templates/story/story.php?storyId=111789560

Jibarra Modern Mexican Restaurant, Raleigh, NC http://www.jibarra.net/

Mary Ann Hansen. Corn Smut. Virginia cooperative extension publication 450-706. http://pubs.ext.vt.edu/450/450-706/450-706.html

Special thanks to Dr. Pataky for help with this blog!

Armillaria Root Rot in the Landscape: Attack of the "Humongous Fungus"

2011-08-24T14:37:00.000-04:00

Armillaria Fruiting Bodies (NCSU PP Slide Collection)

Root rot is one of the most commonly diagnosed disease problems of woody plants in landscapes in North Carolina.
Each year we see dozens of shrubs and trees that have one of the “big three” root rotting diseases: Phytophthora root rot, Thielaviopsis black root rot, or Armillaria root rot.

This post will feature Armillaria root rot. Be on the lookout in the upcoming weeks for posts on Phytophthora root rot and Thielaviopsis black root rot!

Armillaria root rot is caused by species of the fungus Armillaria. Common names for this group of fungi include the oak fungi, shoestring root rot fungi, or the honey fungi, the latter referring to the honey-colored mushrooms the fungus produces.

Armillaria is a common soil inhabitant and can infect a very wide host range including; oaks, maples, azaleas, beeches, birches, boxwoods, cedars, dogwoods, firs, poplars, rhododendrons, yews, roses, spruces, and sycamores (pretty much any woody tree or shrub). It can be destructive in orchards or on fruit trees in the landscape.

Symptoms of Armillaria Root Rot (NCSU PDIC)

Armillaria is typically a problem in older plants or plants that have been stressed due to drought, frost, insect attack, mechanical injuries, poor drainage, low soil fertility excessive shade, or pollution damage. However, it can be an aggressive pathogen under some conditions. Severe infections of young plants in nurseries can result in a quick death. Older or mature plants can withstand infections for several years, resulting in a slow decline, eventually ending with the death of the plant.

Above-ground symptoms include leaf drop, dieback, and an overall decline in plant vigor. On conifers, the crowns of infected plants start to thin and change colors, often turning red, brown, or yellowish. Conifer infections sometimes result in heavy resin flow at the tree base.

Armillaria Symptoms on Juniper (NCSU PDIC)

Armillaria infections start in young roots, but soon the fungus begins to decay larger woody roots. In the early stages of infection, wood becomes slightly grey and can have a water-soaked appearance. Later, the wood becomes light yellow to white and has a soft, spongy rot. Often, rotted areas are offset by black lines of zonation.

Note the black lines of zonation (Photo: Bugwood)

Severely diseased trees can pose significant safety hazards during storms since branches and bases are weakened and can easily break under windy conditions or if under added pressure from snow or ice.

Windthrow Hazard (Photo: Bugwood)

Unlike most plant pathogenic fungi, Armillaria produces mushrooms and other structures that are visible to the naked eye. Three diagnostic signs of Armillaria root rot include:

1. Mycelial Fans: The most common diagnostic sign of this disease can be found beneath the bark (between the bark and the wood) at the base of the tree or shrub. White or creamy paper-like mycelial fans can be observed when the outer bark is carefully peeled away. These white mycelial fans can also be found beneath the bark of infected roots and root collar area.

White Mycelial Fans (Photo: Bugwood)

White Mycelium Under Bark (E. Lookabaugh)

2. Black Rhizomorphs: Sometimes rhizomorphs (dense strings of mycelium) that look like black shoestrings can be found under the bark or throughout the soil around infected tissue. Rhizomorphs serve as one of the primary means of dissemination. Rhizomorphs grow through the soil from infected trees, roots, or old stumps. They are able to directly penetrate healthy roots and cause disease.

Shoestring-like Rhizomorphs (Photo: Bugwood)

3. Honey Mushrooms: In the fall, honey-colored mushrooms can be seen growing near the base of diseased trees and shrubs. Typically, these mushrooms grow in clusters. These mushroom produce microscopic basidiospores, but the spores are not thought to play an important role in the spread of the disease. Most species of Armillaria are edible and are quite tasty. Caution: It is always best to have any mushrooms identified by an expert before you eat them. Eating misidentified mushrooms can be fatal!

Honey Mushrooms (NCSU PP Slide Collection)

Control:

Usually homeowners do not notice Armillaria root rot until the plant is dead or dying. No control is possible at this point and the plant should be removed.

Replanting can be problematic because Armillaria can survive for many years as rhizomorphs in soil or in old wood and stumps. Remove the affected plant and thoroughly dig up and remove all large roots, stumps and any other wood or prunings from the affected area. When planting in areas where a plant has died, or where trees have been removed, as in new construction, remove all old roots, stumps, and wood before replanting. Consider planting ornamental herbaceous or perennial plants or grasses in the area for a few years before attempting to replant woody species.

Healthy trees and shrubs are better able to resist Armillaria root rot than stressed plants. Choose species that are well-adapted to your region and growing site. Maintain their health by fertilizing as recommended, watering during dry spells, and improving drainage in wet areas. When possible, prevent defoliation from insects and foliar diseases. Be careful to avoid damage to roots when digging or tilling. Do not push up soil around tree trunks and do not move soil from affected areas into sites where woody species are growing.

Fun Facts:

This fungus glows in the dark! The mushrooms themselves do not glow much, mainly just the mycelium, giving infected/exposed wood an eerie glow at night. Cutting open a piece of wood with advance decay gives you the greatest chance of seeing the luminescence. Traditionally, glowing wood has been featured in folklore and mythology and termed “fairy fire” or “foxfire.” We do not know the exact reason why the mycelium glows, but we still think it makes this fungus pretty cool!

Glowing Mycelium (Photo: John Denk)

Back in the 1990’s, an article came out highlighting the ability of Armillaria bulbosa to form very large clones. The ability of Armillaria to produce rhizomorphs, allows this fungus to spread out and become quite large, covering great geographic distances. As a result, the phrase “humongous fungus” was born and the media took hold.

UHAUL "Humongous Fungus" (Photo: Tom Volk Website)

Special Thanks to Dr. Larry Grand for Helping with this Post!

Plants Pests and Pathogens

2011-08-22T10:59:00.000-04:00

Greetings,

We hope you can join us for Plants, Pests and Pathogens, Tuesday 8/23/2011 at 10am.

http://www.ces.ncsu.edu/depts/hort/garden/PlantsPestsPathogens/2011.html

You can participate in this two-hour training opportunity for Master Gardeners and Horticulture Agents via your computer, or you can go to one the of downlink sites. To participate from your computer:

Log In by 9:30 am. Include your county with your name and leave the password field blank
Take a few minutes ahead of time to visit the page on How to Use Elluminate. Check to be sure that you have downloaded the free software required to run the program. There are one page reference guides and tutorials available.

In order to minimize interference, please keep your microphone turned off, except when you are speaking to the group.

Schedule for August 23 Session:

10:05 am- Regional Update, Coastal Plains: Cyndi Lauderdale, Wilson

10:10 am-Regional Update, Piedmont: Mary Helen Ferguson, Randolph

10:15 am- Regional Update, Mountain/Foothills: John Vining, Polk County

10:20 am- Featured Speaker: Frank Louws, Organic Disease Management for Vegetable Gardens

10:58 am- Show Stopper Plants: Climbing Hydrangea, John Vining

11:00 am- Entomology: David Stephan, NCSU PDIC, Insect Identification Specialist

11:35 am- Current Issues in Plant Pathology: Mike Munster, PDIC

My Tomato Plants Are Wilting... And Then They Die!

2011-07-19T15:53:00.001-04:00

Tomato Wilting Symptoms (Photo by F.J Louws)

Every summer the Plant Disease and Insect Clinic receives samples from clients who tell us that their tomato plants “wilt and then die.” This can be very discouraging for a home gardener, and devastating for a commercial grower who has a field of plants going down. If you observe these symptoms, be prepared for some bad news!

In the piedmont and coastal plain regions of our state the most common cause of wilting and death in tomatoes is bacterial wilt. The destructive pathogen Ralstonia solanacearum is able to wipe out home gardens and whole fields of tomatoes. It also attacks many members of the nightshade family: tomatoes, peppers, potatoes, and eggplant, along with zinnias, geraniums, sunflowers, and marigolds. Ralstonia causes Granville wilt in tobacco (also a relative of tomatoes), the subject of some of the earliest work on plant diseases at NC State. A bulletin published in 1903 warned growers that curing Granville wilt was “hopeless.”

The most obvious symptom of bacterial wilt is wilting, followed by sudden collapse of the entire plant. Basically, bacteria plug up the water conducting tissue in the stem. The plant is unable to transport water from the soil to the leaves and the plant wilts and dies.

Tomato Collapse (Photo by F.J. Louws)

Burley Tobacco Wilting (Photo by H.D. Shew)

Ralstonia can survive in most soils for years without a host present. When susceptible plants are planted in infested soil, it is only a matter of time before the plant becomes infected. A heavy rain or watering can help bacteria move through soil to the roots of susceptible plants. A few large black roots are often found where the infection got started. This is especially evident in infected tobacco plants.

Black Roots Where Infection Took Place
(Photo by H.D. Shew)

If you suspect bacterial wilt, there are quick and easy diagnostic checks you can do yourself. The first thing you need to do is check for vascular browning inside the stem. Tomato stem tissue should be very light green. The easiest way to check for vascular discoloration is to cut the stem, as shown in the image below.

Tomato Stem: Note Brown Discoloration
(Photo by M.J. Munster)

Vascular Browning (Photo by E.C. Lookabaugh)

Next, check for bacterial ooze. The easiest method is to cut the stem off at the base. Take the stem cutting and hang it over a glass of water (shown below). After a few minutes, you should be able to observe a cloudy stream of bacteria oozing from the cut tissue. It is very important not to disturb the glass of water during the test.

Bacterial Stream Test (Photo by M.J. Munster)

Note White Bacterial Streaming (Photo by M.J. Munster)

Sometimes, it can be hard to see the bacteria. If you have access to a microscope, take a thin slice of brown vascular tissue and place it in a drop of water on a glass microscope slide. Make 2 straight cuts across the tissue (cutting the tissue into 3 pieces). Put a cover slip on top and look through the microscope using the 10x objective. Within seconds, you should be able to see dark brown plumes of bacteria oozing from the slices.

Slice Vascular Tissue on Glass Slide
(Photo by E.C. Lookabaugh)

Micrograph of Bacterial Ooze
(Photo by E.C. Lookabaugh)

If you don’t see any bacteria, you probably don’t have bacterial wilt. Fusarium wilt can cause vascular browning and is common in the Piedmont. Most modern varieties of tomatoes are resistant to Fusarium wilt, but we see it often in heirloom varieties. Southern blight or high soil salts are other potential causes of browning. Another wilt disease, Verticillium wilt, is present in many mountain areas, and has other distinctive symptoms.

Arrow Pointing to Bacterial Ooze on Tobacco Stem
(Photo H.D. Shew)

Arrow Pointing to Bacterial Ooze on Tomato Stem
(Photo by E.C. Lookabaugh)

Much as in 1903, if your plants have bacterial wilt, there is nothing you can do to save them. Infected plants will not recover and should be removed and destroyed. Replanting with new plants will not solve the problem because they will likely become infected and die too. The bacteria can persist in the soil for years, so it is best not to plant susceptible plants back into that area. Rotation with non-host plants, for example, sweet corn, for at least three years is recommended.

Growing tomatoes in containers with potting soil is one option if your garden is infested. Be sure that the containers are not in contact with the native soil and be careful not to spread infested soil to new locations.

For commercial growers, some soil treatments and the use of resistant rootstocks and grafting can be an option for the following year. More information on root grafting can be found here:

http://www4.ncsu.edu/~clrivard/TubeGraftingTechnique.pdf

For a look at the history of the Department of Plant Pathology and Granville wilt in North Carolina agriculture, see http://www.cals.ncsu.edu/plantpath/FromLabtoField.pdf

Special thanks to Dr. David Shew for helping with this posting!

My Blueberries Look Funny...

2011-07-08T12:38:00.000-04:00

Written by Bill Cline

In July, blueberries are ripening all across the state. These excellent little berries can be grown in your back yard, but you may not know that they are also our most valuable commercial fresh fruit crop. Growers in southeastern NC harvest hundreds of acres beginning in May each year, and each year the clinic receives diagnostic samples of berries affected by diseases, insects and weather. Here are a few of the problems we have diagnosed recently:

Mummy Berry

Mummy berry is caused the fungus Monilinia vaccinii-corymbosi. This fungus overwinters on the ground underneath blueberry bushes, and in spring produces a cup-shaped mushroom that releases spores. These spores infect and kill emerging leaf shoots, causing the primary, or shoot blight phase, of the disease. These blighted shoots then produce a second type of spore that is carried by insects to the flowers, where the secondary, or fruit infection stage takes place. The end result is “mummies” – berries that do not turn blue, but instead turn pink or salmon-colored and fall to the ground. Mummy berry can be controlled with fungicides, through the use of resistant cultivars, by removal of infected fruit, and by mulching to bury any mummies remaining on the ground.


Mummy Berries: Infected berries are pink (Photo by Bill Cline)

Fruit rots

Fruit rotting fungi cause soft, leaky or “fuzzy” berries (visible spores or mold). Blueberries are more resistant to decay than other small fruits, but still need to be harvested in a timely fashion to avoid fruit rots. Berries do not ripen all at once, but are picked over several weeks. Highbush blueberries should be harvested every four or five days, while rabbiteye blueberries are harvested every seven to ten days (rabbiteye blueberries are the most common backyard species in North Carolina). It is important to “clean” the bush at each harvest date by removing all blue fruit, to avoid having overripe, leaky berries in later pickings. If the bushes are wet with dew or rain, wait until they dry before harvesting, since handling wet berries greatly increases post-harvest decay.

Blueberry Fruit Rot (Photo by Bill Cline)

Exobasidium

Exobasidium vaccinii is a fungus that causes a “green spot” symptom on blueberry fruit and can also infect leaves. This disease is becoming increasingly common in commercial fields and has also been diagnosed on blueberries in other states. Little is known about this fungus on blueberry, and no control measures have been established. The disease occurs sporadically and seems to be associated with high humidity -- low or sheltered parts of fields where air movement is limited.

Berries infected with Exobasidim (Photo by Bill Cline)

Insects in berries

Blueberries are sometimes infested with larval stages of insects, including blueberry maggot fly, cranberry fruit worm, cherry fruit worm, Plum curculio and a new pest, spotted-wing drosophila. All these pests are controllable, but must be properly diagnosed since control measures vary. Cherry fruitworm and cranberry fruitworm are frequently encountered in unsprayed fields. The cranberry fruit worm produces “frass” that looks like a small clump of sawdust on the outside of a cluster of berries, while cherry fruitworm usually affects only two berries, “gluing” the two together and producing frass only inside the fruit.

Cranberry fruitworm frass (looks like sawdust) (Photo by Bill Cline)

Hail damage

There has been quite a lot of hail this year resulting in damage to blueberry fruit. Affected berries are usually damaged in spring while the fruit is still green. Initially only bruised or dented, hail-damaged berries develop scars and cracks as they swell and ripen, and these symptoms can be confused with disease or insect damage. Where hail damage is suspected, look for tattered leaves as further evidence of a hail event.

Hail damage on blueberries (Photo by Bill Cline)

Japanese Beetles Out in Full Force This Season

2011-06-29T10:57:00.000-04:00


Robber fly eating Japanese beetle (Photo D. Stephan)

Barbara Shew, our clinic director, said that she observed the cardinals in her yard putting on quite a show a few days ago. They were knocking Japanese beetles from her crape myrtle flowers and then chasing the beetles as they tried to fly away. I guess sometimes cardinals delight in chomping down some beetles in addition to their usual diet of seeds. Cardinals are not the only animals that enjoy the occasional beetle treat. My cat, Slinky, loves eating Japanese beetles. She catches them, knocks them out with her paws, and then carries them to the hood of the car. After letting them cook all day in the sun, she goes back and eats them! Predatory insects, like robber flies, assassin bugs, and others will feed on the adults. Unfortunately, humans do not get the same satisfaction from finding these beetles in their yards.

Japanese beetles emerge once per year to feast on a variety of ornamental and crop plants. Their favorite ornamental hosts include roses, rosaceous trees, shrubs such as crab apple, crape myrtle and linden, grape, and fruit trees.

Typically, Japanese beetles feed on the upper leaf surface eating the tissue between leaf veins. This gives the leaves a lacy appearance, a type of damage called skeletonizing.


Japanese beetle and skeletonizing damage (Photo: B. Shew)

They generally consume entire petals of roses and other flowers. Beetles aggregate on plants in response to chemicals (odors) released by damaged plants and pheromones released by female beetles. The resulting hungry masses of beetles can rapidly devour trees, shrubs, vines, and flowers.

Japanese beetle damage (Photo: B. Shew)

After they have fed for a while, the female beetles burrow into soil to lay their eggs. Grubs (larvae) hatch from the eggs and feed underground through the rest of the summer and fall. Female beetles and the grubs prefer moist soils, so a damp summer means more beetles the following year.

The beetle grubs may be serious pests of the roots of grasses and shrubs, especially on turf farms and golf courses. They burrow through the soil feeding on roots. This can result in areas of dead grass. The grubs overwinter deeper in the soil, and in the spring, they move just below ground level, complete feeding, and pupate. New beetles emerge from pupae in late spring to start the cycle again.

Japanese beetles can fly long distances, so beetle traps do not offer any protection to landscape plants. They may actually attract more beetles to your yard! Likewise, treating a lawn for Japanese beetle grubs will not reduce damage from incoming beetles.

Long-term protection for landscape and nursery plants can be achieved through the use of neonicotinoid insecticides such as imidacloprid (e.g., Merit, Marathon II) or acetamiprid (Tri-Star). Acelepryn (chlorantraniliprole) is a new product with extremely low vertebrate toxicity but good efficacy against a number of pests, including Japanese beetles.

Japanese beetle on flower (Photo: B. Shew)

For more information on the biology and management of adult Japanese beetles in nurseries and landscapes, consult Ornamentals and Turf Insect Information note No. 146 at:
http://www.ces.ncsu.edu/depts/ent/notes/O&T/flowers/note147/note147.html
http://www.ces.ncsu.edu/depts/ent/notes/O&T/flowers/note44/note44.html

Special thanks to Steve Bambara and Dave Stephan for their help with this post!

It Looks Like a Dog Threw Up in My Mulch: Slime Molds - Harmless but Ugly!

2011-06-14T18:21:00.000-04:00

Fuligo Septica in Mulch
Photo by Donna Steinbach (Submitted to PDIC)

Every year, we receive image samples depicting the “dog-vomit” slime mold.

People see this ugly growth on their mulch and immediately want to get rid of it! The culprit is a slime mold known as Fuligo septica. In spite of their names, the slime molds are not true fungi, but are related to amoebas, algae, and paramecia. These fascinating organisms spend part of their lives inconspicuously creeping through mulch, leaf litter, etc., engulfing bacteria and bits of organic matter. Through some sort of environmental or chemical signal, they switch to the spore-producing phase of their life cycle. In the case of Fuligo septica, the spore-producing fruiting body appears as a bright yellow froth that quickly forms a pinkish crust covering the dark powdery spores inside. These spores will blow away and start the cycle over again. The fruiting body can simply be raked out of the mulch or washed off with a hose. It is not toxic, although some people are allergic to the spores.

Fuligo Septica Slime Mold
Photo by Donna Steinbach (Submitted to PDIC)

The dog vomit slime mold is not a plant pathogen. However, slime molds sometimes will grow on plant parts that touch the affected mulch, as seen on the end of a gardenia branch in the picture below.

Slime Mold on Gardenia
Photo by Mike Munster

Fuligo septica is often seen in hardwood mulches. It is less of a problem in pine bark or cedar mulches. It is usually worse the first year mulch is applied than in subsequent years.

While dog vomit is one of the most noticeable slime molds, many other types can be found in most back yards.

Here are some other slime molds we have seen lately.

Physarum Slime Mold
On Annual Ryegrass and a weed (Carolina geranium)
Photo by Mike Munster

Physarum Slime Mold
On Cucumber
Photo by Anne Edwards

Slime molds can be startling, but up close they can be startlingly beautiful. See the collection of images by Georgia resident Ray Simons here.

Special thanks to Mike Munster for helping with this blog idea!

Attack of the Killer Tomato (Spotted Wilt Virus)

2011-06-10T12:48:00.001-04:00

TSWV fruit symptoms
Photo by F. J. Louws

Lately, we have seen a lot of tomato samples with tomato spotted wilt (TSWV) come through the clinic. TSWV is a virus that is spread by at least seven different kinds of tiny insects known as thrips. It takes only 15 minutes of feeding for a tomato plant to become infected, and once TSWV is acquired, there is no cure. TSWV is sporadic in nature with heavy disease pressure in some years relatively little disease pressure in others. Due to this unpredictable nature, and the broad host ranges of thrips, controlling TSWV can severely challenge traditional pest management practices.

TSWV can be a major problem both in greenhouses and in the field and can affect field crops like tomato, peanut, and pepper, tobacco along with many ornamental plants. On tomatoes, symptoms may be expressed on leaves, petioles, stems, and fruit. Early symptoms include cupping and off-colored bronzed foliage. Later, leaves may show small, dark spots and eventually die. Dark brown streaks can be seen on stems and petioles. Plants may be severely stunted and new growth can be deformed. Sometimes the plant may exhibit one-sided growth. The tops of the plants may turn yellow and wilt.

TSWV foliar symptoms
Photo by E. C. Lookabaugh

Fruit symptoms are very distinctive. Immature fruit have mottled, light green rings with raised centers. Mature fruit has a unique red/orange mottling that can make the fruit unmarketable.

TSWV immature fruit symptoms
Photo by F. J. Louws

TSWV mature fruit mottling
Photo by E. C. Lookabaugh

In North Carolina, tobacco thrips (Frankliniella fusca) and western flower thrips (F. occidentalis) are the two most common vectors. Tobacco thrips are able to spread the virus from nearby weed hosts before they can be killed by insecticides applied to the crop. Early infections usually result in the greatest impact on yield because early infections can prevent flowering and fruit set. Secondary spread within fields is very uncommon but may occur by large populations of western flower thrips. Western flower thrips are extremely difficult to control because they are highly tolerant to insecticides and prefer to reside deep within the blossoms where it is difficult to reach with insecticides. In addition to spreading TSWV, thrips alone can be damaging to crops because of how they feed. Thrips feeding causes the collapse of plant cells which leads to deformed plant growth, flower deformation, and silvery areas and flecking on expanded leaves.

Two common TSWV vectors
Photo UGA

Controlling this disease is very difficult. In home garden settings, there is usually little secondary spread after the first wave of infections in the spring when virus-bearing thrips are moving from winter weeds to garden plants. You may wish to remove infected plants, especially those that were infected before fruit set, because they will not recover.

TSWV field symptoms (left plant showing severe stunting)
Photo by F.J. Louws

In a field setting, it is important to manage weeds adjacent to the field because these weeds harbor both the thrips vector and the virus during the winter. Infected plants should be removed and destroyed as soon as symptoms appear. TSWV resistant varieties are available and can be effective. Organic growers and other larger acreage growers may want to consider reflective mulches to cover their beds rather tha the traditional black mulch. In greenhouses, thrips populations should be eliminated so they, along with TSWV, are not spread to the field when seedlings are transplanted.

More information on managing this disease can be found here, under "Viral Diseases"

Special thanks to Dr. Louws for helping put together this post and for supplying images!

Now That's Just Peachy!

2011-06-03T09:32:00.000-04:00

My favorite time to visit the local farmers market is during peach season. To me, there is nothing tastier than slicing open a juicy peach on a hot summer day. Right now, there are three major peach diseases that you can be on the lookout for: bacterial spot, peach scab, and brown rot. The next time you visit the local market or if you have a peach tree in your backyard, try and see if you can spot some of these diseases for yourself!

Bacterial Spot

Dr. David Ritchie, the peach “disease” guy here at NCSU, says that, this year, bacterial spot is the worst he has seen since 2003 and the most damaging it has been in the past 20 years on highly susceptible cultivars. Bacterial spot is caused by the bacterium Xanthomonas arboricola pv. pruni. The most obvious leaf symptoms are yellow, chlorosis of the leaves with angular lesions at the leaf tip, mid-rib, and along the leaf margin. Premature leaf drop is common in infected leaves. Foliar lesions appear water-soaked and sometimes grayish in color. As lesions age, centers may become dark or purple in color and necrotic, eventually dropping out to result in a shot-hole appearance.

Bacterial Spot Symptoms
(Photo by D.F. Ritchie)

Twig symptoms consist of cankers on either side of leaf and flower buds on the previous year’s growth. These cankers are called “spring cankers” because they are first visible during bloom. “Summer cankers” can be seen on current-season growth and are visible early to mid-summer.

Bacterial Spot Twig Symptoms
(Photo by D.F. Ritchie)

The earliest fruit lesions are normally seen about three weeks after petal all. Fruit infection is favored by moist and warm conditions with fruit being very susceptible from shuck split to pit-hardening. Developing lesions have a water-soaked appearance with small necrotic centers that become black in color and enlarge as the lesions mature. Early infections result in lesions that expand down the pit before harvest. Infections later on in the season result in shallow lesions that cause skin cracking. Attempts to control bacterial spot at this time in the season (June) are of little to no value because once the bacteria have infected, the “path” to damage has occurred.

Bacterial Spot Fruit Symptoms
(Photo by D.F. Ritchie)

Peach Scab

Peach scab occurs every year in North Carolina. This disease is caused by the fungus, Cladosporium (syn. Fusicladosporium) carpophilum. C. carpophilum is an asexual fungus that produces conidia and chlamydospores. The conidia are wind or water splashed dispersed and infect shoots, leaves, and fruit during the season. Chlamydospores are thick-walled survival structures that form on infected twigs during the winter. Usually the leaf infections are less noticeable and least important. The twig infections are ecologically important because they serve as the site for the production of the overwintering chlamydospores. Fruit infections result in considerable yield losses because of grade reductions or culling of affected fruit that would be less desirable in the marketplace. First fruit infection occurs during the 4-week period after bloom. The fungus has a long latent period of approximately 6 weeks before the scab lesions are observed, usually by the end of May to early June. Greenish-gray to olive circular spots form on the fruit and these spots expand in size as the disease progresses.

Peach Scab
(Photo by D.F. Ritchie)

The fungus sporulates on the fruit lesions, producing conidia that can cause secondary infections of fruit and twigs. Fruit scab lesions often have a raised, corky appearance, whereas bacterial spot lesions are often sunken in appearance. Severe infections may lead to cracking of the fruit skin, which can serve as entry points for fruit-rotting organisms like the brown rot fungus. There are no resistant varieties or cultural control options for managing peach scab. Control relies exclusively on well-timed fungicide applications starting at petal fall and making 2-3 applications during the following 4-5 weeks. Once scab is observed, fungicide sprays will have little if any controlling effect of scab on the fruit.

Brown Rot
Brown rot is most risky in warm, humid climates. Brown rot is caused by the fungus, Monilinia fructicola. This disease occurs in two phases: a twig and blossom blight phase and a fruit rot phase. Twig and blossom blight phase occurs in early spring when the trees are blooming. Infected blossoms wilt, turn brown, and usually cling to the twigs. The infections can then spread into the twigs resulting in twig cankers. Fruit susceptibility to brown rot increases during the 2 to 3 week period prior to harvest because of the increased sugar content in the fruits. Initially, tan-brown circular spots can be seen on the fruit.

Brown Rot
(Photo by D.F. Ritchie)

Under humid conditions, ash-gray-brown spore masses are visible on infected tissue. There can be thousands of spores on each lesion and each spore is capable of initiating a new infection. If conditions are wet and warm during fruit ripening, the entire crop can be destroyed overnight! Controlling this disease relies primarily on good sanitation practices combined with judicious use of fungicides. Fungicides are most effective when applied just before the blossoms open and then again during the 2-3 week period leading up to harvest.

More information on peach production and diseases can be found in the "Peach Growers Handbook"

Hopefully these diseases won't keep too many peaches from ending up in your basket at the local martket! Enjoy!

Special thanks to Dr. David Ritchie for providing his peach disease expertise and photos!

First Slime Flux Sample of the Year Arrives in Clinic

2011-05-19T15:10:00.000-04:00

Slime flux on white oak
(Photo by: Randy Cyr, Bugwood)

The first slime flux sample of the season was sent to the clinic today, as a digital image from a Raleigh homeowner. This is a problem we usually associate with the warmest months of the year. Slime flux is a foul-smelling and unsightly seepage of sap from the trunk of shade trees. Slime flux occurs in apple, birch, elm, hemlock, maple, mulberry, oak, poplar, and willow. In North Carolina, slime flux is quite common in the landscape on large, mature oaks, tulip poplars, and elms. In oaks, the fluxing usually occurs on the lower portion of the trunk, close to the ground.

The underlying cause of slime flux is a condition called wet wood, which develops when bacteria ferment the sap within the wood. These bacteria enter through wounds, usually in the roots. The affected wood turns dark and appears water soaked. As the sap is fermented, methane and carbon dioxide gases can be produced. If the internal pressure from the gas becomes great enough, the fermented sap seeps out of cracks or wounds and down the bark. The flux is colorless to tan at first, but darkens upon exposure to the air. As fluxing continues, large areas of the bark can become soaked.

Many different microorganisms grow in the flux, which results in a foul or alcoholic smell. Various types of insects, including bees, wasps and butterflies, are commonly attracted to it.

Some dieback may occur in severely affected trees, but often the fluxing stops after several weeks or months with no apparent damage to the tree. The slime flux may be triggered by heat, drought, or other stresses, so try to maintain good growing conditions. There is no curative treatment for slime flux, but it will do no harm to remove loose bark over the area. Wet wood and slime flux are one more reason to avoid causing wounds to tree roots.

For more info: Click Here

My plants have a little sugar coating :) Powdery Mildew Spotted in the Landscape

2011-05-17T13:40:00.000-04:00

Powdery Mildew on Crape Myrtle
(Photo: H.D. Shew)

Powdery mildew has started to show up on many landscape plants. Powdery mildew is easily diagnosed on most plants by the characteristic coating on leaves that gives this disease its name. The “powder” will not rub off – it is actually the mycelium and spores of the disease-causing fungus.

Powdery mildews frequently infect dogwoods, crape myrtles, roses, lilacs, tulip-trees, oaks, and numerous other shrubs and perennial plants. In addition to the powdered appearance, typical symptoms include discolored and distorted leaves, shoots, and flowers. Although powdery mildews rarely cause serious damage to most hosts, severe cases can result in defoliation or poor growth.

PM on fruit
(Photo: H.D. Shew)

PM on flower stem
(Photo: H.D. Shew)

While most powdery mildews look the same to the naked eye, hundreds of different species of fungi cause powdery mildews. Most are specific to a particular host. Under the microscope, different groups of powdery mildews can be identified by their highly distinctive cleistothecia (specialized spore-bearing structures).

PM micrograph
Note hooked appendages
(Photo: H.D. Shew)

PM micrograph
Note branched appendages
(Photo: H.D. Shew)

In the spring, cleistothecia from previous infections rupture and release wind-blown spores. These spores land on susceptible plant tissue and begin to grow on the surface and into the upper layer on the leaf. The fungus produces columns of asexual spores that are capable of causing new cycles of infection. Late in the season, the cleistothecia appear as tiny dark specks embedded in the mildew. These contain the sexual spores of the fungus and will overwinter to start new infections in the spring.

Black cleistothecia embedded in mycelial mat
on leaf surface (Photo: H.D. Shew)

Powdery mildew is most common in cool or warm and humid weather conditions, but it may occur and cause severe damage in warm and dry climates. Temperatures between 70-80 degrees F and a relative humidity between 85%-100% favor infection. Powdery mildew pathogens are some of the only fungal organisms that can germinate and infect in the absence of free water. These fungi require high humidity but are not dependent on wet leaves for infection and spread. Excess leaf wetness actually inhibits spore germination.

Management:
Cultural Control:

Purchase mildew resistant varieties
Reduce humidity: Increase air circulation and light penetration by thinning and pruning plants to reduce overcrowding
Avoid planting susceptible plants in shaded areas
Sanitation: Prune out dead and diseased tissue and rake and remove any fallen tissue to reduce the chances of the fungus surviving until the following season
Overhead watering of the leaves: Water inhibits spore germination for most powdery mildews, but be careful because excess leaf wetness can increase chances of other foliar diseases.
Avoid practices that stimulate succulent growth: Powdery mildews are obligate parasites that prefer fresh, succulent plant growth. Applying nitrogen fertilizer, pruning heavily, and watering excessively are not recommended because they promote succulent growth.

Powdery mildew on dogwood (Photo: H.D. Shew)

Chemical Control:

Chemical control is often not necessary in the landscape because this disease rarely kills the plant. Spraying trees such as dogwoods and crape myrtles can be impractical.

Fungicides may be used to control powdery mildew on highly susceptible varieties of roses and other plants that suffer severe symptoms and damage.

See Rose Diseases and Their Control in the Home Garden
Rose Diseases Link

Sweet Sounds of Springtime

2011-05-10T13:48:00.001-04:00

Periodical Cicada. Photo by Susan Ellis Bugwood

One of my favorite things about summertime in the south is the humming and buzzing of cicadas. The distinctive buzzing noise that fills the air across the south is the male’s mating call. Right now, brood XIX of the periodical cicadas are waking up and preparing to swarm. Brood XIX are periodical cicadas, meaning that all members of the brood emerge in the same year. Brood XIX, also known as the Great Southern Brood, has been living underground since 1998. This is the country’s largest brood, stretching across 12 states.

Every summer, the dog-day cicadas (Tibicen sp.) come out and fill the air with their mating calls. These cicadas are larger than the periodical cicadas and have green markings. The periodical cicadas are smaller, with hints of orange or red to their bodies. This year, we will have the opportunity to see and hear both types of cicadas. Periodical cicadas sing and fly in spring, whereas other species of cicadas are active during the summer.

Cast "skins" and cicadas that were
unsuccessful emerging at base of tree.
Jordan Lake area. Photo by Steve Bambara

Both types of cicadas have a life cycle that takes them from tree to soil and back to tree again. The life cycle of the Brood XIX periodical cicada takes 13 years to complete, while the speedy dog-day cicadas take only 2-5 years and are not synchronized with each other. Several other broods of periodic cicadas emerge only once every 17 years!

After spending 2-17 years in the soil, cicada nymphs dig their way to the surface. In late May or early June, the nymphs crawl to the trunk of a tree or some other tall object, and cling there. Soon the insect molts into the winged adult stage, leaving behind the cast skin. The shells left behind are fun to play with and also give back nutrients to the tree as they decay.

Cast skins clinging to sweet gum branch. Jordan Lake area
May 9, 2011.
Photo by Steve Bambara

Adults are active during the daylight hours. Males begin to sing with a shrill buzzing noise to attract the females. After mating, females used their sawlike ovipositors to split open the bark of hardwood twigs and insert their eggs. After 6 or 7 weeks, the eggs hatch and tiny ant-like first stage nymphs drop to the soil to burrow for the next 2 or more years. While in the soil, the nymphs feed on the roots of trees.

Split twigs showing egg deposits. Photo NCSU

Aside from their daytime racket, the cicadas are otherwise harmless. The only damage from cicadas occurs when they split tree twigs to lay their eggs. This causes tip dieback (or natural pruning!), which is only a problem on a tiny tree.

It is neither practical nor desirable to try and eliminate cicadas! They provide an abundant food source for local predators… a tasty buffet for birds.

Watch this neat video from Charlotte NC and hear the cicadas in action!

For more information: click here
Special Thanks to Stephen Bambara, NCSU Entomology for information and photos!

Fusiform Rust: What's that orange stuff on my pine tree?

2011-04-26T13:01:00.000-04:00

Just last week, I noticed the galls on the pine trees in my back yard started bursting open with the bright orange spores of fusiform rust. Fusiform rust is a damaging disease in landscapes and forests of the South. The most obvious symptom is spindle-shaped swellings or galls on the branches or trunks of pine trees.

Fusiform rust is caused by the fungus Cronartium quorum f. sp. fusiforme. Like many rust species, this fungus produces five different spore types and completes its life cycle on two different hosts: pine and oak.

During the spring, the fungus produces bright orange spores like the ones I observed on the galls. Typically, these spores are produced from late March to mid-April. Wind-blown spores infect newly formed leaves of several oak species, especially water, willow, and laurel oaks. Symptoms on oak are not conspicuous and usually the tree is not harmed. The fungus produces a different type of orange spore on the under-surface of oak leaves from late April through the middle of June. These spores are then wind-blown to nearby pines where they create new infections, causing new galls and continuing the cycle.

Pine trees are highly susceptible to Fusiform rust when young and infections that occur within the first 5 years of growth usually result in death. Later, main stem cankers can girdle and kill the tree or reduce its value. Stems with cankers are weak and susceptible to wind and ice breakage, and galls easily catch fire and stay afire. Secondary infections by the pitch canker fungus (Fusarium moniliforme var. subglutinans), black turpentine beetles (Dendrodoconus frontalis) and coneworms (Dioryctria spp.) aggravate the tree’s weakened condition, causing further damage.

Over the years, fusiform rust has become an increasing problem, particularly in pine plantations. Loblolly and slash pines are the most susceptible tree species. Longleaf is fairly resistant and shortleaf is highly resistant.

Management options include spraying fungicides, planting longleaf or shortleaf pines in areas with histories of severe rust infections, pruning branches with rust galls less than 15 inches from the stem, eliminating nearby oak hosts, and using rust-resistant clones.

For more information click here,

Red Bay Ambrosia Beetle Found in North Carolina!

2011-04-25T14:17:00.002-04:00

The North Carolina State University Plant Disease and Insect Clinic, in communication with U.S. Department of Agriculture and North Carolina Department of Agriculture & Consumer Services, has corroborated the presence of red bay ambrosia beetle in North Carolina. This tiny exotic beetle was first detected in North Carolina this March, in Bladen County, by the North Carolina Forest Service.

Red bay ambrosia beetle transmits laurel wilt pathogen.
(Image Michael C. Thomas, Bugwood)

The red bay ambrosia beetle, Xyleborus glabratus, and the fungus Raffaelea lauricola, together constitute an insect/disease threat.

The beetle transmits the fungus which causes the disease known as laurel wilt. The combination is generally fatal to red bay, which is an important maritime forest species and is also sometimes found in the landscape. The decline of red bay may have secondary implications for some animals and other plant species.

Other plants in the laurel family, including sassafras, are also susceptible to the fungus. This disease complex a serious threat to the avocado industry in Florida.

Symptoms of laurel wilt.
(Images James Johnson, Bugwood)

For more information, click here

More information on Laurel Wilt will be presented in tomorrow's Plants, Pests, and Pathogens elluminate session.

Herbicide Injury to Tomatoes

2011-04-19T17:28:00.001-04:00

"Classic" Glyphosate Symptom

Recently, the clinic has received several tomato plants with symptoms of herbicide damage. Glyphosate (found in products like Roundup) causes very distinctive yellowing symptoms at the base of tomato leaflets. Broad-leaf weed killers (2,4-D type herbicides) cause stunted and deformed new growth, and whipping and curling of the leaves.

2,4-D Injury

Tomatoes are very sensitive to herbicide injury and damage can be severe. In extreme cases, simply touching tomato plants with herbicide-contaminated hands or clothing can cause injury.

Spray drift is an important source of herbicide damage. Sometimes symptoms appear in a gradient pattern, with plants closest to source being more affected than those further away.

Be careful to prevent herbicide drift into home gardens, farms, or greenhouses where tomatoes are growing. To reduce the chances of spray drift, do not apply herbicides near these areas on windy days.

Glyphosate Drift in Greenhouse

Some herbicides are formulated to provide season-long protection against weeds. Planting sensitive crops too soon after using one of these herbicides can cause injury. Check the product label to see when it is safe to replant following herbicide application.

Glyphosate Injury

Sometimes farmers and home gardeners report problems in vegetables and flowers after applying hay, manure, grass clippings, compost, or other amendments to soil. Symptoms include poor seed germination, twisted, cupped, and elongated leaves, and misshapen fruit. Young plants may die and yields may be reduced in mature plants. This damage can be traced to herbicide carryover in the soil amendment. For more information on herbicide carryover in soil amendments, click here.

Be on the Lookout for Camellia Petal Blight

2011-03-21T15:41:00.001-04:00

Petal blight is very common on camellias in the spring. It is caused by the fungus Ciborinia camelliae. Although petal blight can affect both japonica and sasanqua camellias, it is usually seen in early spring when japonica camellias are in bloom. Disease development is favored by frequent rain showers, high humidity, and mild temperatures during bloom.

The disease is first seen as brown spot on the expanding flower petals. In the early stages of disease, veins within the spots appear darker than the surrounding tissue, giving some blooms a distinctive netted appearance.

Camellia petal blight: Note the distinct netted appearance

The spots quickly increase in size and often extend into the base of the flower, causing the entire flower to fall to the ground. A ring of white fungal growth may be visible where the blossom was attached to its base.

Camellia petal blight: Fallen blossoms

Camellia petal blight: Note the white ring of fungal growth at the base of the flower (top of image). Later, very large sclerotia are produced at the flower base

The blighted petals are dry or leathery but do not crumble when handled. Petal blight can be confused with cold injury, but cold injury is usually found on the outer petals, which become dry and crumbly and do not fall from the plant. Flowers from the same plant can have petal blight and cold injury.

Several weeks after the petals fall to the ground, hard black fungal structures similar in size to a chickpea may be found at the base of the flower (seen above, lower right). These sclerotia can persist in the soil for several years. Under favorable conditions (cool weather followed by warm, wet weather), the sclerotia germinate to produce tiny mushroom-like structures. The “mushrooms” produce airborne spores that land on nearby camellia flowers, starting a new cycle of disease.

Camellia petal blight: Mushroom-like structures produced from sclerotia germination

How to Control Petal Blight

Fungicide sprays can be used to control petal blight, but sanitation is the key to controlling this disease in the landscape. Because sclerotia produced in diseased flowers are the source of future infections, the best way control petal blight disease is to remove all fallen flowers and debris from the ground around camellia plants. The sclerotia are too large and hard to be completely destroyed by composting, so infested debris should be disposed of completely. Remove old mulch each spring and lay a layer of fresh bark or pine straw around the base of each plant. The mulch will interfere with the spread of spores from previous years’ infections.

** Be sure not to add more than 1inch of mulch. Burying the root system by adding 2 or more inches of mulch may kill the plant!

A milestone

2011-03-13T10:40:00.000-04:00

This morning, Friday 3/11/11, the ten thousandth sample was entered into the PDIC database, which went online in January 2008.

Plants, Pests, and Pathogens Webinar

2011-02-20T11:35:00.000-05:00

Greetings,

We hope you can join us for Plants, Pests and Pathogens, Tuesday 2/22/2011 at 10am.

Log In by 9:30 am. Include your county with your name and leave the password field blank
Take a few minutes ahead of time to visit the page on How to Use Elluminate. Check to be sure that you have downloaded the free software required to run the program. There are one page reference guides and tutorials available.

In order to minimize interference, please keep your microphone turned off, except when you are speaking to the group.

Schedule for February 22 Session:

10:05 am- Regional Update, Coastal Plains: Bob Filburn, Edgecombe County Horticulture, Apiculture, Local Foods Initiative, and Forestry-- Green Thumbs on Wheels
10:10 am-Regional Update, Piedmont: David Goforth, Carbarrus County, Horticulture
10:15 am- Regional Update, Mountain/Foothills: Cliff Ruth, Commerical Horticulture, Henderson and Transylvania Counties-- Weed Scouting Class
10:20 am- Featured Speaker: Hannah Burrack, Assistant Professor of Entomology and Extension Specialist, tobacco and Small Fruits
11:00 am- Entomology: David Stephan, NCSU PDIC, Insect Identification Specialist, 40 years experience
11:35 am- Current Issues in Plant Pathology: Mike Munster, PDIC, Plant Pathologist and Diagnostician of Commercial Ornamentals

Prime Weather for Paper Wasps

2011-02-14T21:01:00.003-05:00

You aren't the only one heading outside to enjoy the beautiful weather... female paper wasps have started leaving their winter homes and may soon be seen swarming yours!

Paper wasps (Polistes spp.) eat a lot of insects and are usually considered beneficial to the landscape. They are best known for their open, grey paper nests built under an open porch ceiling, window sill, or any type of overhang. During their nesting phases, paper wasps can be defensive and are likely to sting you if you disturb their nests.

During the cool/ cold times of the year, when their are no nests or young to protect, paper wasps show types of swarming behavior. In the fall, this behavior is connected with mating. Male wasps look for the best place to "hang out" and attract the females. Dozens or even hundreds might be seen around the upper stories of buildings and other tall towers. Males locate a good perch, camp out, and release odors (pheromones) to attract the pretty female wasps. Some time after mating, the males die and the females seek a shelter for winter.

During winter and early spring, on any warm day (like the one's we've been seeing this week!), these wasps become active. If their shelter is inside a wall, chimney, or vent, they may follow the light into the inside of a structure rather than moving outside. The only risk is unknowingly coming into contact with the wasp and being stung. The future queens become active on warm days and start flying around, however they are not particularly defensive and are unlikely to attack. This flying behavior disappears at the end of the day when temperatures drop and the wasps resettle.

The best management and control of these wasps indoors is a rolled-up newspaper. Aerosol pesticides work, but they cost money and aren't particularly necessary if you are able to whack the wasps with a paper or fly swatter.

For more information on Paper Wasps click the link below:

Paper Wasp Information

Special Thanks to Steve Bambara and Michael Waldvogel for this great Insect Note!

Elluminate Training Sessions: URL Links and Instructions

2011-02-10T12:11:00.000-05:00

Below are the links for the Elluminate (interactive webinar) sessions on Plant Disease Diagnostic Training.

February16:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261500568610
February 23:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261500568609
March 2:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261500568608
March 9:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261500568607

If you have never used Elluminate before, follow these instructions:

Our Elluminate session Plant Disease Diagnostic Training, is scheduled for the above dates. You can connect to the session by clicking the above links to the sessions.

Before connecting to Elluminate for the first time, make sure to complete the Configuration setup. You MUST do this at least 24 hours ahead of time.

Please use the same location and equipment that you will use when you attend the actual Elluminate session(s) to complete the following steps:

Go to http://www.elluminate.com/support
Make sure Step 1 shows a checkmark or says that you have Java installed. If you do not see a checkmark, follow the instructions to obtain the latest version of Java.
Enter the Configuration Room as outlined in Step 2. Follow the directions in the Configuration Room to test your audio setup.

If you have ANY PROBLEMS configuring Elluminate, call 866-388-8674, option 2. Elluminate Live! support is available 24 hours day, 7 days a week.

To join the session:
1. Go to the Elluminate meeting URL (links above).
2. Under section 2, "User Authentication", select "Guest."
3. Type in your email address.
4. Type in your name.
5. Type in the session password if prompted.
6. Click "Log In."

If you have any problems logging in to the session or hearing the audio, call 866-388-8674, option 2.

County Agent Training in Plant Disease Diagnosis

2011-02-07T15:51:00.006-05:00

The Plant Disease and Insect Clinic and the Department of Plant Pathology announce agent training in plant disease diagnosis. The training will consist of four one-hour Elluminate sessions covering the basics of plant disease diagnostics and one all-day hands-on session. In order to accommodate as many County Agents as possible, the hands-on session will be held twice, on the 18th and 25th of March. All County Agents are encouraged to participate in the Elluminate sessions. Seating is limited to 20 people for each of the hands-on workshops. There is no fee for this training.

The training sessions and dates are as follows:

February 16, 2011, 10:00 a.m.

Introduction to Plant Disease Diagnosis: Types of plant problems; signs and symptoms of plant diseases; the diagnostic process

February 23, 2011, 10:00 a.m.

Using the Plant Disease and Insect Clinic: Sample collection and submission; using the database; interpreting diagnostic results; resources and information

March 2 and March 9, 2011, 10:00 a.m. (participate in both sessions)

Tips for diagnosing common plant diseases of specific crops and ornamental plants; recognizing diseases that threaten North Carolina agriculture and landscapes

March 18, 2011 and March 25, 2011, 8:30 – 4:30 (attend one all-day session only)

Hands-on workshop in plant disease diagnosis.

Sessions are limited to 20 County Agents each, with priority given to agents hired in the past five years. These sessions will illustrate signs and symptoms on live material in the laboratory and in the landscape, will demonstrate simple techniques that can be used by County Agents in the field or at their office to make a diagnosis, or to provide preliminary information to a PDIC diagnostician or Extension Specialist. The session will also provide training in digital photography skills as they apply to plant disease diagnosis. Agents will tour the PDIC and will “walk through” the process of diagnosing a clinic sample. Lunch, breaks, educational materials, and reimbursement of travel expenses (breakfast and mileage) will be provided.

Contact Barbara Shew at barbara_shew@ncsu.edu for more information or to sign up for the all day sessions.