Late Blight Has Arrived

Over the past 2 weeks, late blight, caused by Phytophthora infestans, has been knocking on the doors of our state. Aided by the monsoon-like weather we’ve been experiencing the past few weeks, our unwelcome guest has finally managed to get inside and start to wreak havoc. Late blight was officially confirmed on tomatoes from Guilford County on July 2nd. Today we diagnosed late blight on a tomato sample from Wake County and on a sample of tomatoes and potatoes from Watauga County.

Late blight can be a devastating disease on tomatoes and potatoes. Without proper preventative measures, late blight can completely defoliate and destroy a crop within one to two weeks.

The first symptoms of late blight on tomato leaves are irregularly shaped,
water-soaked lesions. (Photo: K. Ivors)

More information about tomato late blight and how to control it can be found in this tomato late blight factsheet produced by Dr. Kelly Ivors and in our earlier blog post. 

More information on potato late blight and how to control it can be found in this potato late blight factsheet produced by Dr. Lina Quesada-Ocampo.

Videos and additional management recommendations for tomato and potato are available in the USAblight website. Here you can track the late blight epidemic and register to receive text and/or email alerts when new disease outbreaks are reported.

Blame it on the rain (Part II): Reprise of the slime molds

An aerial view of a grove of strange trees? Read on.

With all this wet weather we can expect to see a lot of plant diseases in the upcoming weeks. Oddly enough, damage due to root rots won't be evident on trees and shrubs until the weather turns hot and dry. That's when the damaged root systems won't be able to keep up with the demand for water in the foliage. All this is a story for another day, however. Today I want to revisit a group that was a blog topic two years ago: the slime molds. (See our archived post.) These are sometimes called myxomycetes, but don't let the Greek suffix fool you; they are not related to true fungi.

Stemonitis sp. (Photo: Matt Bertone)

We had several inquiries about slime molds during the last week of May. Fortunately they do no harm to plants, animals, or people, though some folks have been shown to be allergic to the spores. One inquiry was accompanied by a spectacular photo - not reproduced here - of Diachea leucopodia on grass blades. Another was the specimen of Stemonitis - probably Stemonitis fusca - pictured at right. It had been picked up off of a living room baseboard. This particular slime mold is usually associated with wood, sometimes indoors. The photo at the top of this blog was taken on a stump in Schenck Forest in Raleigh several years ago. In both pictures you can clearly see the thin "stipe" or stalk that supports each cylindrical spore-bearing "sporangium".

Remnants of slime mold fruiting on Japanese holly

A third specimen from that same week was submitted by one of our campus landscapers. She was concerned about white material on the foliage of a Japanese holly. This turned out to be another slime mold. Most of the sporangia had broken off, but a the base (called the hypothallus) was still stuck to the leaves. This particular case is covered in the "Geeks Corner" below.


Then yesterday while out looking for leaf spots on maples, I noticed some whitish gray tufts in a mulched bed in the shade of several trees. It turned out to be yet another slime mold, Acyria cinerea. The tiny sporangia are only about a millimeter-and-a-half tall, not counting the stipe. If you look closely, you can see that they are often in clusters.Within these sporangia, the white spores are held by a network of spiny threads called a capillitium. The characteristics of the capillitium are important in slime mold identification.

Capillitium and spores of Acyria cinerea at 400x.

Fruiting of Acyria cinerea on mulch

What we are seeing in all these cases is the end-game of the slime mold's life cycle. If the wind-dispersed spores land and find the right conditions they'll germinate into ameoba-like cells that will eventually become a multicellular, macroscopic, living film called a plasmodium. This plasmodium will slowly "crawl" or ooze around on wood or bark, in leaf litter, on dung, or on other materials. They almost always escape notice at this stage, during which they "feed" by engulfing bacteria, fungal spores, and probably  bits organic matter. Eventually the plasmodium switches gears and changes over to spore production, treating us to one of nature's great works of art. The Georgia Museum of Natural History has posted a gallery of myxomycete images by photographer Ray Simons.

Fruiting of Fuligo septica

Not every member of this group is quite as lovely. Fuligo septica, the "dog-vomit" slime mold, is gross in both the German sense of "large" and the English sense of "repulsive". It is very common on hardwood mulch and was highlighted in our June 14, 2011 blog. When the plasmodium first comes to the top of the mulch and before becoming a crust-covered mass of spores, it's basically a bright yellow froth. A picture of a more mature fruiting is shown at left. Up close, they don't look so bad, actually.

Sporangia of what is probably Physarum leucopus.
The width of this photograph covers only a quarter inch.

Geeks Corner. The slime mold pictured at right baffled me for a while. As a non-expert in this group, I was having trouble deciding whether there was lime in the capillitium or not. There are clearly lime deposits on the peridium (outer covering), giving it a frostly look. Using Martin & Alexopoulos's 1969 tome The Myxomycetes, I eventually keyed it out to Physarum leucopus. The reference states, "Before the peridium breaks, this species is remarkably similar in appearance to Didymium squamulosum." The key distinctions: white nodes in the capillitium, the lack of a columella, and the fact that the lime on the peridium exists as granules rather than crystals.


For anyone interested in learning more, I highly recommend starting with Stephenson & Stempen's book Myxomycetes: A Handbook of Slime Molds (1994. Timber Press).

Blame it on the rain (Part I): A multitude of millipedes

In the last couple weeks we have gotten a lot of rain. This can have both positive and negative impacts on pests and pathogens. One critter I have been getting a lot of calls and emails about is the greenhouse millipede, Oxidus gracilis (Polydesmida: Paradoxosomatidae).

The greenhouse millipede (Oxidus gracilis) is one of the most common arthropods around. It can be distinguished from other millipedes by the size (~1"), brown color, and especially by the groove going across the top of each body segment
Photo by Matt Bertone

Millipedes are in a group of organisms, closely related to insects and spiders, called myriapods (which translates literally to "many-legs"). At first they may appear to be worms, but they have legs which worms lack. The most familiar are centipedes and millipedes, some of which grow to large sizes (some tropical centipedes are a foot long and can eat bats, lizards and rodents!!). While centipedes are carnivorous and have venom, millipedes are vegetarians that feed on decaying plant matter. Though they cannot bite, many millipedes defend themselves with toxic poisons that either taste bad or can cause sickness - but only when eaten. This is the reason why some millipedes you see are brightly colored and smell like almonds (related to the cyanide compounds they produce):

A larger relative of the greenhouse millipede (Polydesmida: Xystodesmidae) [~1.5" long]
Photo by Matt Bertone

The greenhouse millipede is a non-native species from Asia that has traveled throughout the world with humans. They are abundant under rocks and logs, in basements and in the soil - anywhere where there is some moisture. People tend to notice them sporadically until some event drives them out of hiding. In the case recently, our heavy rains from multiple storms have saturated the soil and make it difficult to survive for the millipedes. Their response is usually to move to higher ground like the foundations and walls of homes and other structures. They may even move inside, though if they get stuck it's bad news for them as they will inevitably die, and bad news for homeowners who have to clean up the carcasses and deal with a distinct odor they produce. In addition, their movement can sometimes be caused by them avoiding chemicals/pesticides that have been sprayed around their habitat, especially the mulch and gardens next to homes.

Greenhouse millipedes invading people's space.
Photo from Stokes Co., NC

Control, especially in the chemical sense, is usually not warranted. Simply vacuuming up the critters is often enough to get rid of them. They pose no harm to people and little to no harm to plants (sometimes becoming important in greenhouse situations - hence the name). So if you are seeing a lot of these worm-like organisms after rains or chemical treatments, be aware that the situation is (A) temporary and (B) the millipedes are harmless (some large ones even make great pets!).

Quick guide to centipedes and millipedes (and other look-alikes):

Does it have legs? 

> If not then it is likely a worm (though some maggots and other critters are similar):

Typical earthworm.
Photo by Matt Bertone

> If yes, but only up to six true, jointed legs (all on thorax) then it is an insect, likely a larva (caterpillar, grub, etc.):

A click beetle larva (Elateridae) - note only the thorax region has true legs.
Photo by Matt Bertone

> If yes and many legs then you have a myriapod*!

(*unless you have an isopod - pillbugs and sowbugs)

BUT is it a centipede or millipede?

> If it has one pair of legs per segment and is generally fast-moving then it is a centipede (also see house centipedes):

A typical stone centipede (Lithobiomorpha).
Photo by Matt Bertone

> If it has two pairs of legs per segment and is generally slow moving then it is a millipede:

A granulate millipede (Polydesmida: Polydesmidae: Scytonotus granulatus)
Photo by Matt Bertone

Landscape Professional Field Day 2013

Post co-written by Matt Bertone & Mike Munster

Attendees enjoying the nice weather!

On May 15th, the NCSU PDIC set up shop temporarily at the 2013 Landscape Professional Field Day, held at the beautiful JC Raulston Arboretum. This small gathering focused on a half-day program of informative talks for those working mainly with landscape woody ornamental plants. While industry reps were showing their wares and the speakers were informing attendees of the newest issues in landscaping, we brought our microscopes and tools to get down and dirty with samples brought to us by meeting members.

Mike at the booth, full of samples from us and clients.

We prepared for it the day before by scouting local plants for disease and insect damage to use as "show-and-tell" examples. From the clinic we brought an arborvitae riddled with weevil damage (see this post for details), imported willow leaf beetles (one of the individuals seen here), Armillaria infected wood and a few other things. Matt brought in a number of samples from his yard including maple eye-spot midge galls, some dogwood with powdery mildew, camellia leaf gall (Exobasidium camelliae) and oak leaf blister (Taphrina caerulescens). We also had a Nandina showing "shoestring" foliage typical of infection by Cucumber mosaic virus.

Mike identifying diseases for a client.

Throughout the day we met new people and caught up with colleagues and clients. A few brought us some problems to diagnose, including an unhappy trio of containerized Liriope, one of which had classic symptoms of Fusarium crown rot. There was a sample of Eastern red cedar (pictured at right) that had to be brought back to the lab for diagnosis. Symptoms of Phomopsis tip blight and Kabatina tip blight are very similar. This one turned out to have Kabatina.A yucca leaf from there at the arboretum was found to have anthracnose, caused by the fungus Colletotrichum.

Matt at the scope with some sort of critter.

On the critter side, a client brought some lovely tree hoppers (see below) that were congregating on an oak in Wake Co. Matt assured him they were merely flashy and would not harm a mature oak. Later a graduate student working on witch-hazel (Hamamelis) at the arboretum was curious about strange growths on the leaves of the trees. Matt would tell you what they are, but that would ruin an upcoming blog post about them!

An oak treehopper (Platycotis vittata). Males and females may be horned or hornless.

All in all it was a beautiful day and it felt good to get outside - warm weather, interesting people/samples and a grill full of hot dogs makes for a great time! Until next year...

No Joke: Tomatoes are Cracking Up

Photo: Debbie Roos

Tomatoes are cracking up after the recent rains, but growers are not amused. Recently, we’ve seen in an increase in the amount of tomato surface cracking. Tomato cracking is an abiotic disorder of tomato fruits that is associated with growing conditions. When tomatoes are left on the vine too long or during periods of rapid fruit growth, the tomato epidermis (or skin) does not have enough elasticity to compensate for the sudden growth. Eventually the skin splits and bursts.

There are two main types of growth cracks 1) radial cracking, which is splitting of the skin from the stem scar towards the blossom end and 2) concentric cracking, which is splitting of the skin in a circular pattern around the stem. Radial cracks occur during humid, hot weather. Concentric cracks occur during rapid fruit growth associated with rainy weather following a period of dry weather. The earlier growth cracks occur during fruit development, the more damaging they are. Growth cracks can provide the perfect entry point for secondary fruit rotting organisms.

Photo: Debbie Roos

The most important means of controlling growth cracking is maintaining a steady, adequate supply of water or irrigation flow, especially during hot, dry conditions. Avoid over and under irrigating. Mulching also will help prevent dramatic fluctuations in soil moisture. Be especially wary if weather was cool and overcast followed by sunny, hot, and dry periods, and then high humidity and rainfall. Keeping foliage healthy and disease free is also critical. If the fruit lacks leaf cover, cracking can be more of a problem. Remove mature fruit right after heavy rains to prevent cracking. Follow recommendations from Cooperative Extension about plant nutrition, because high nitrogen and low levels of potassium can contribute to fruit cracking. Some varieties are more prone to cracking and can show cracking when the fruit are still green. Even varieties that show some resistance to cracking in the green stage may crack once the fruit starts turning red. Plum varieties like ‘Heinz’ and ‘Marglobe’ crack less than cherries and the larger fruited varieties like “Better Boy.” If you have a history of tomato cracking in your tomatoes, you may try switching to one of these varieties, ‘Daybreak’, ‘Jet Star’, ‘Pink Girl’, ‘Monte Carlo’, ‘Mountain Fresh’, ‘Mountain Spring’, and ‘Spitfire.’ New varieties are released regularly, so check with your local cooperative extension agent for latest variety recommendations for tomatoes.

by: Emma Lookabaugh, Chris Gunter, and Barbara Shew

Proud Papa - Twice in One Month!

As I revel (quite sleepily) in the fact that I have a new little daughter, I am also very happy that my other babies from a clinic sample have been "born". Since I started this position I have been watching a trunk section of arborvitae (Thuja sp.; 'Green Giant' variety) that was submitted from Holly Springs (Wake Co.) following the decline and death of some trees.

Affected arborvitae (Thuja sp.) along the road.

When I first saw the section I observed a few large holes - about 1/4 inch in diameter - in the top with sawdust being pushed from them. This was clearly a boring insect, but was it a metallic wood borer (Buprestidae), longhorn beetle (Cerambycidae), or something else? Turns out, after prying some of the bark back, there were several large (up to 3/4 inch), legless larvae boring just under the surface. The larvae were very clearly weevils (Curculionidae), but what species?

Weevil larvae preserved for future study.

Because larval weevils are nearly impossible to identify, it was my goal to rear the larvae until they emerged as adults so I could then identify them. I waited...and waited...and waited. Some beetles (under the right conditions) can exist as larvae in wood for decades and even up to 50 (!) years - I wasn't going to wait that long. Fortunately, after removing a little more bark some weeks later I found pupae. Finally, adults in progress! A week or so later and I had adults which I identified as the cypress weevil (Eudociminus mannerheimii (Boheman)).

Cypress weevil (Eudociminus mannerheimii) showing life stages and damage.

This fairly large weevil (10-17 mm) is known from a few hosts, especially baldcypress (Taxodium distichum), but also Japanese cedar (Cryptomeria japonica), Leyland cypress (Cupressocyparis leylandii), and arborvitae (Thuja sp.). It's biology appears to be similar to the related pine regeneration weevils, Hylobius pales (Herbst) and Pachylobius picivorus (Germar). The beetles lay eggs on weakened or dying trees and the larvae burrow beneath the bark before creating a deeper hole to pupate in. Adults appear to emerge in the Spring and will feed on the bark of small, green branches. Because they generally attack already-declining trees they are not always the main issue. However, this sample had so many weevils in one small section that I believe they were a major factor causing health issues for the trees. Follow the links below to read more about this weevil and learn about management practices. In the mean time I am going to smoke my proverbial cigar and curate these specimens to go into the NCSU Insect Museum which only had four total specimens!

LINKS:
NCSU Entomology Insect Note on Eudociminus mannerheimii
UF Featured Creatures on Eudociminus mannerheimii

Be on the Lookout for Cedar Apple Rust

Most of us who live in the triangle are hoping for rains to wash away the yellow film of pollen coating our cars, houses, and sidewalks. Spring rains also jump start the most bizarre life-stage of cedar apple rust, a common disease that affects apple trees (and crab apples) and eastern red cedar trees.

Galls on cedar (Photo: H.D. Shew)

The cedar apple rust pathogen (Gymnosporangium juniperi-virginianae) requires two hosts and four spore stages to complete its complex life cycle. On cedar trees, the most obvious signs of infection are firm brown galls, which are about the size of a golf ball and are usually found scattered on the tree’s branches and twigs. After a heavy rain, the galls produce striking bright orange gelatinous horns, which are composed of millions of spores called teliospores. In dry periods, the horns can be seen as short spikes covering the galls. If you find a gall with dried horns, cut it out of the tree, place it in a glass of water and watch over the next few hours as the horns expand.

Gall with dry telial horns (Photo: H.D. Shew)

The cycle of wetting and drying can continue several times during the spring, and in each cycle the teliospores germinate and give rise to another spore type, called basidiospores. These basidiospores are forcibly discharged into the air and are wind-blown to nearby apple trees.

 Apple leaves and fruit are most likely to be infected when they are wet and temperatures range from 46 to 75 F. Yellow to orange spots are produced on the upper surface of the apple leaves one to two weeks after infection. The spots on leaves may be raised or swollen and infected fruit may be slightly distorted. Small black dots within the lesions signal the production of the next spore type, the pycniospores (also called spermatia). One to two months later, fringed cup-shaped structures (aecia) appear on the underside of the apple leaves and these contain aeciospores, yet another spore type.

The aeciospores are windblown to cedar trees in late summer to early fall, where they germinate and infect to produce galls. The galls produce teliospores in the second year after infection, completing the life cycle. G. juniperi-virginianae survives in the gall tissue for only two years. After its second year, the spore producing year, the pathogen dies in the gall tissue. On apples, the pathogen survives only a few months, just long enough to produce the aeciospores that infect cedar trees.

Symptoms on apple (Photo: E.C. Lookabaugh)

Cedar apple rust causes only minor damage to cedar trees from twig dieback. Damage to apple is more significant and can result severe defoliation and fruit blemishes. Since this pathogen requires both hosts to complete its life cycle, control can be achieved by eliminating one host from the surrounding area, although oftentimes eradication is not feasible or desirable. Additional control measures include the use of disease-resistant apple cultivars, properly timed fungicide applications on apple, and removal of cedar galls before spring rains.

Check out this cool video of telial horns expanding (Video: Arlene Mendoza-Moran)

More information about the 2013 strawberry virus outbreak

Many of you probably have seen an article in today's Raleigh News and Observer about virus problems in this year's strawberry crop. The Plant Disease and Insect Clinic has received several strawberry samples with virus problems in the past few months.

Here are some comments from Dr. Frank Louws, Extension Specialist for Strawberry Diseases in NCSU's Department of Plant Pathology about the strawberry virus situation:

This link will take you to an excellent article from Dr. Chuck Johnson at Virginia Tech about this year's strawberry virus outbreak. All the information for Virginia is true for NC and other states with this problem. The main question growers ask is: “What can we expect in yields?”. We have only limited experience with these viruses in our annual systems. However, we had a case of Strawberry Mild Yellow Edge Virus (SMYEV) in 2004, as shown below in Sweet Charlie plants photographed at full harvest. About 25 to 30% of the plants were affected by the virus and the virus dramatically affected plant growth and yield, as seen in the picture. This year, two viruses, SMYEV and Strawberry Mottle Virus (SMoV), have been diagnosed from problem fields. We do not know how these viruses will affect crop yields in 2013, but some reductions are expected. Specific recommendations for dealing with this problem can be found in Dr. Johnson’s article. With good management, this problem should not recur in future years.