Sample of the Week: Botrytis Blight of Pansy

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

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

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

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

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

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!

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

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.