Meet Our New Vegetable Pathologist

Hello, my name is Lina Quesada (pronounced Lena Kesada in case you were wondering). On March 1st of 2013 I joined the Department of Plant Pathology at North Carolina State University as an Assistant Professor and Extension Specialist for vegetable pathology. I am originally from Bogota, Colombia (not Columbia!) and came to the US in 2006 to work on late blight of potato at the Ohio State University.

Shortly after that I moved to Lansing, Michigan and started a PhD in Plant Pathology at Michigan State University working with Phytophthora capsici, an important pathogen of cucurbits and solanaceous crops. While working on my PhD I fell in love with the boy in the lab next door and married him on 2010, the same year I finished my PhD.

I stayed at MSU and did a postdoc working on cucurbit downy mildew and bacterial canker of tomato. After that I did another postdoc working on corn postharvest diseases caused by Fusarium, a soilborne pathogen that can also affect sweetpotatoes and vegetables. My husband and I moved to NC a few weeks ago and have really enjoyed this beautiful state and its kind people. I am very excited to be here and have the opportunity to work with the clinic and all of you during the next few years to address challenges you have with vegetable diseases. If you need to contact me my information can be found here.  You can follow me on Twitter, Facebook or LinkedIN if you wish and I am in the process of making a lab website that will be posted to the link I just provided to quickly disseminate any findings or materials produced by my program.

The New Bug Guy

Hello everyone! My name is Matt Bertone and I am the new entomologist for the Plant Disease & Insect Clinic. I will be taking over for the now-retired Dave Stephan, a great entomologist with years of encyclopedic knowledge who will not be easily replaced. I do hope to follow in his footsteps, however, and to learn as much as I can about the insects and other animals that affect the daily lives of North Carolinians. But first, let me tell you a little bit about myself.

I was born up North (don’t hold it against me) and lived most of my formative years in Pennsylvania. From a young age I was obsessed with the natural world (see below photo). It started with the usuals like dinosaurs and such, but quickly turned into a passion for insects, spiders and other creepy-crawlers¹. They were so strange and diverse that there was always something amazing to learn.

Only the nerdiest kids know how to draw
a microscope in kindergarten.

After high school I entered college at Salisbury University on the Eastern Shore of Maryland. I had a great time there and took as many zoology courses as I could. There I met many great scientists and was introduced to research studies and continuing to graduate school. I was not aware of the universities that had entomology programs and applied to NCSU on a whim after seeing one of my colleague’s certificates from the department. After applying I was very happy to be accepted and had no idea how wonderful the area, school and people were going to be.

In 2001 I started my master’s work on dung beetles (Scarabaeidae & Geotrupidae) inhabiting cattle pastures in the Piedmont (Salisbury, NC) and coastal plains (Goldsboro, NC) under the advisement of Dr. Wes Watson. The project was great. I was introduced to a charismatic group of insects, researching their seasonality, abundance and diversity, and performing experiments to show how they help fertilize different soils. I was also happy to participate in extension work, since teaching in any format is another passion of mine.

A rolling dung beetle (Melanocanthon bispinatus)
from North Carolina.

In 2004 I began my PhD work under Dr. Brian Wiegmann on the evolution of true flies (Diptera), one of the most underappreciated – yet extremely diverse – groups of animals. I used genetics to see how different groups of the more “primitive” flies, like mosquitoes and midges, were related to one another. It was eye opening to learn the things flies do and I could (and may well in the future) go on and on about them. Needless to say, I found another group to love².

The elephant mosquito (Toxorhynchites), a large and distinctively blue fly, 

is one of the few beneficial mosquitoes. Larvae eat other mosquito larvae and adults do not bite. This male was sucking goldenrod nectar in Garner, North Carolina.

Following my degrees I have worked on various projects including a computer-readable glossary for the anatomy of wasps, bees and ants (Hymenoptera) and a citizen science project on the arthropods (insects, spiders and relatives) that are found in Triangle homes (a project through NCSU and the NC Museum of Natural Sciences).

Now I’m here in the clinic! I am very excited to help people find out what little leggy things are on their plants, eating their crops, and inside their homes. Please feel free to send photos or specimens to the clinic. I will do my best to get an ID, so that a specialist can recommend the proper action. All said, I hope to serve science and the citizens of North Carolina well in this position!

Other facts about me:

• I am a huge (literally and figuratively) insect geek, competing in many insect quiz bowls (Linnaean Games) during my time at NCSU
• I am an avid insect macrophotographer (my Flickr) and graphic designer
• I enjoy music, movies, games and cooking
• Last but certainly not least, I have an amazing wife and daughter, and a baby on the way (as well as two dogs)

¹ I also love reptiles, amphibians, fish, and many other groups of organisms (even plants!)
² I highly suggest anyone interested in flies read Harold Oldroyd’s captivating tales in The Natural History of Flies – it is very easy to read except for some scientific names (which you can just pretend are like the variously named creatures from Tolkien or Dr. Seuss!)

Entomologist David Stephan to Retire

(Special thanks to Dr. Jack Bacheler, whose words formed the nucleus of this blog.) 

David Stephan, circa August 1973

After almost 40 years, David Stephan will step down from his position as the Entomology Specialist for the Plant Disease and Insect Clinic. Dave has been responsible for the identification of all insects, spiders, mites, and many other kinds of pests submitted to the Clinic by the public, extension agents, consultants, pest management companies, and researchers. Dave developed a reputation for being able to identify anything dead or alive that walks, digs, flies or swims. He was often called upon to identify the cause of arthropod plant damage even in the absence of physical remains of a pest.

Also a competent herpetologist, Dave additionally carried out a number of special identification and research projects with NCSU faculty, other scientists and students; worked closely with personnel from the NCSU Insect Museum; and was extensively involved with homeowner and agent training in the identification of insects and other arthropods. He was a regular presenter on satellite (later internet) training sessions broadcast several times a year to Cooperative Extension Agents and Master Gardener Volunteers.

David Stephan, April 2011

Dave's knowledge is not only broad, but deep. Beyond being able to identify many "critters", as he calls them, he also knows their life cycles and natural history. He has spent thousands of hours on the phone explaining insects and what they can and cannot do. We celebrate with Dave that he'll now have more time to spend in his beloved outdoors and doing the sorts of entomological taxonomy he enjoys, without the pressures of the clinic.

Beyond his formidable technical skills, Dave's diversity of interests and talents will be missed in the PDIC. Without Dave's black belt in the art of bad puns, the clinic will be a safer but duller place. He is a connoisseur of weather, of new words, of motion pictures, and of science fiction, particularly the Star Trek and Babylon 5 series. In spare moments we've chatted about everything from Broadway show tunes to the refractive index of diamonds. His is a mind that makes connections.

Last week, colleagues old and new joined to thank Dave for his many contributions to the Plant Disease and Insect Clinic, the Entomology Department, the North Carolina State University Extension Service and to the citizens of North Carolina. Since a replacement entomologist has not yet been hired, there will be a period of time during which insect identification services will not be available at the clinic. Please see the announcement on our home page for details.

Dave, don't forget: live long and prosper.

Is your heater hurting your tomato plants?

Tomato pollution damage (Photo: E. Lookabaugh)

Winter may have finally arrived, and with it, a serious issue for greenhouse growers. Over the past few weeks, the Plant Disease and Insect Clinic has received several tomato samples showing symptoms of pollution damage. The most common greenhouse pollutant is ethylene. Ethylene is an odorless, colorless gas which acts as a plant hormone. Ethylene is a growth regulator in plants, and excess ethylene is harmful to greenhouse crops. Tomatoes are particularly sensitive to ethylene and other pollutants like propane. Repeated exposure to very small amounts (0.01 ppm) over several days or exposure to higher amounts (1 ppm) for several hours can result in injury. 

Tomato pollution damage, twisted leaves (Photo: E. Lookabaugh)

The most common symptoms of ethylene exposure on tomatoes are epinasty (a downward bending of growth that causes plants to appear droopy even though they are not wilted), flower drop, and twisting of the upper leaves. 

Tomato pollution damage, pale leaf spots (Photo: E. Lookabaugh)

Tomato plants exposed to high levels of propane gas can have superficial stem lesions on one side of the plant (the side that faces the heating system) and leaves with tan to white lesions between the veins. Tomatoes will usually recover once they are no longer exposed to pollutants.

Tomato pollution damage, stem lesions, flower death/ drop (Photo: E. Lookabaugh)

Tomato pollution damage, superficial stem lesions (Photo: E. Lookabaugh)

Tomato pollution damage, stem lesions
and flower drop (Photo: E. Lookabaugh)

Faulty heating systems are usually the cause of pollution damage. The major causes of gaseous pollutants in a greenhouse system include dirty or improperly adjusted heating units, cracked heat exchangers, leaky gas lines, chronic use of unvented heaters, and exhaust from combustion engines. Pollutants can build up in the greenhouse when temperatures are borderline, causing heaters to kick on and off many times during the night. Exhaust from heaters that are not vented properly will lead to a build-up of incompletely combusted gases. Additionally, the any exhaust remaining in the exhaust pipe will flow back into the greenhouse. Alternatively, if nights are very cold and the heater runs a lot, insufficient oxygen feed can result in incomplete combustion and pollution damage.

Here are a couple of solutions to pollution issues in your greenhouse system.

1. Under cold conditions when ventilation systems are shut down, make sure the heater has access to a sufficient supply of oxygen. The grower may need to add an air intake source that feeds the heater.
2. Make sure pollutants are properly exhausted. If there is a crack in the heater or exhaust pipes, pollutants will remain in the greenhouse. There should be a small fan in the exhaust pipe that blows for about 20 seconds after the heater (and the heater fan) shuts off to be sure all pollutants exit the exhaust pipe. In a "vent-free" system, the first and last puffs of air should be exhausted because "vent free" heaters are 99% efficient except when they start and stop.

For more information on ethylene damage: click here 
For more information on faulty heaters: click here

Out of the Firewood and into the Parlor

Redheaded ash borer. Photo: Mike Wilder, NCCES

These striking photos were submitted to the PDIC as an online image sample. Several of these insects had been found crawling around furniture in a Rocky Mount, North Carolina residence. Our soon-to-retire entomologist Dave Stephan identified them as the redheaded ash borer, Neoclytus acuminatus, one of the most commonly reported of our "firewood beetles." Although it is called the redheaded ash borer, it can infest many different species of hardwood trees. Dave also provided the following information about this interesting situation.

Redheaded ash borer. Photo: Mike Wilder, NCCES

There are several species of longhorned beetles which can emerge from firewood in homes. Most of the species encountered this way in North Carolina belong to the genera Euderces, Megacyllene, Neoclytus and Phymatodes. Typically, females of these species lay their eggs in the bark of recently cut, storm damaged, or dying trees. The hatching larvae tunnel into the wood and complete their development in one year, although some species may take 2-3 years. Longhorned beetles in general spend their grub-like larval phase burrowing in wood, eventually pupating there. There is a certain chilling requirement for the insect to break diapause (hibernation). In simple terms, if the wood stays out in the cold long enough, the insect's body is primed for spring. When the wood is brought into the house, the warmth tricks the beetles into thinking that the winter has passed, and the adults emerge. Dave suspects that the insect is as surprised as the homeowner to find that it has emerged into a strange habitat. He says that the chance is "less than zero" that they will cause damage to wood products in the home, since they must lay eggs on a "green" tree with intact bark. They do not sting, transmit disease, or carry off children, but could bite (just a pinch) if handled roughly. To avoid the problem in the first place, burn firewood within two to three weeks of bringing it inside.

Firewood can be a means of moving more serious pests, too. See Rob Trickel's Guest Blog from November 5, 2012 for more information.

They're heeeere . . .

We've been enjoying some balmy days here in Raleigh, NC. So balmy, in fact, that our Japonica camellias are starting to bloom -- and when the blooms begin, petal blight cannot be far behind. A quick look under the camellias in front of Nelson Hall confirmed our fears. The tiny, mushroom-like apothecia of Ciborinia camelliae were popping out all over (below).

These tiny mushrooms bear the spores that infect the camellia blossoms. We generally miss the chance to spray for petal blight, but if you can catch it just as the apothecia emerge, you might be able to control it with fungicides. Later, the best control is to pick up all the spent and diseased blossoms as soon as they fall to the ground. This will reduce the number of apothecia that are produced the following spring.

For more information about petal blight, see our earlier blog post here.

For information about fungicides that control petal blight, see http://www.aces.edu/pubs/docs/A/ANR-0416/ANR-0416.pdf
Be sure to check with your local County Extension office to get the latest information about fungicide labels and use. Follow all label directions.

The Once and Future Chestnut

"Chestnuts roasting on an open fire…"

Dr. Larry Grand on chestnut. August 2004.
Photo: Caroline Vernia

I can count on the burned fingers of one hand the number of times I've eaten chestnuts, but for some of you they may be an important part of your holidays. A century ago – back the last time folks were dating their letters 12/21/12 – the American chestnut, Castanea dentata, was one of the most prominent trees of the eastern North American forest, from New England down the Appalachians and areas to the immediate west and south (range map). Apart from the prized wood, these trees provided nuts that served as food for humans and wildlife. There was a problem, though. From the area around New York City a blight was spreading. By the time Mel Tormé and Bob Wells had penned "The Christmas Song" in 1944, most of the native range of the American chestnut had been affected by the disease. Now most of the chestnuts are gone from their original range. The picture at left was taken in 2004 and shows retired NCSU forest pathologist Larry Grand standing on the remains of a once great chestnut tree (I don't actually know the cause of death in this case.)

Fruiting bodies of Cryphonectria parasitica
on the trunk of a chestnut tree. October 2006.
Photo: Marc Cubeta

So what happened? This was another case of an introduced fungus causing widespread destruction on a plant species that had not evolved resistance to it. See the discussion of coevolution in our Dec 3rd blog, if you missed it. The fungus Cryphonectria parasitica had been brought accidenetally from Asia on seeds or seedlings. This fungus causes branch and trunk cankers that eventually girdle and kill the tree. Of all the tree species susceptible to C. parasitica, the American chestnut is the most seriously affected. The fungus reproduces by spores formed in orange-colored fruiting bodies on the bark (picture at right). Two types of spores are produced: one that spreads by wind and one that is transported by birds, insects, or water splash. When spores reach a wound on a chestnut tree they germinate, and the fungus infects. According to information provided by the American Chestnut Foundation, it takes only 2 to 10 years for a mature chestnut tree to die. For more information on the disease process, see the March/April 2012 issue of the Journal of the American Chestnut Foundation. 

Unfortunately this sort of scenario has repeated itself with increasing frequency and rapidity as efficient transportation systems have allowed us to move plants and their diseases around the globe. In October 2011, the disease called "box blight" was first found in North America. Within months it had been found in nine US states and one Canadian province, and it hasn't stopped spreading. This has implications not only for the nursery industry, but for the cut greens industry this time of year. For more information about this threat specific to boxwood and Pachysandra, see Dr. Kelly Ivors' box blight information pages.

Chestnuts. Western NC. October 2006.
Photo: Marc Cubeta

Returning to the chestnut trees, it is an interesting fact that the roots are not killed by the fungus, so new sprouts can repeatedly develop. Eventually, though, this new growth succumbs to the blight. Back in October of 2006, one of our professors came across a chestnut tree in the North Carolina mountains that had grown large enough to bear nuts, though it was clearly infected with chestnut blight (picture at left). I suspect it is gone by now.

Concerted efforts to bring the chestnut back have been going on for some time. Different strategies have been attempted, the most important of which is to cross the native species with resistant species, principally Castanea mollissima, the Chinese chestnut. Another approach was to inoculate trees with a weak (“hypovirulent”) form of the fungus that prevented the deadlier version from killing them. The main reason these strains are weak? They themselves have a viral infection! The 2004 Annual Review of Phytopathology contains an analysis of this situation. (For those unfamiliar with the term, "phytopathology" is the study of plant diseases.) Sadly, one of the hurdles faced by growers trying to re-introduce the chestnut is yet another disease: root rot caused by the fungus-like organism Phytophthora cinnamomi.

Wishing a safe and enjoyable holiday season to all our readers from the NCSU Plant Disease and Insect Clinic! Note that we will be closed December 24th through January 1st, but looking forward to serving you in 2013.

Nematodes in the Tree Tops

Deodar cedar, NCSU Campus
Photo: M.J. Munster, PDIC

Japanese black pine, Wilmington, NC.
Photo: John Wooldridge, NCCES.

What do the two trees in the foreground of these images have in common? They are both infected with the pine wood nematode. This pest also goes by the name "pine wilt" nematode and by the jaw-breaking scientific name Bursaphelenchus xylophilus. That's a big name for roundworms less than a millimeter long. They also are narrow and nearly transparent, making them difficult to see without a microscope. The micrograph below shows swarms of them emerging from a bit of infected wood that was placed in water. Although they are called pine wood nematodes, they can invade a number of genera of conifers in addition to pines.

Bursaphelenchus xylophilus
Photo: NCDA&CS Nematode Assay Laboratory, Weimin Ye

Let me back up a moment for those not familiar with the Phylum Nematoda. Nematodes in general are extremely abundant on our planet, but relatively few cause economic damage. Most species are marine - ask your children if they've seen them on "Sponge Bob." Most of the terrestrial types are not parasites but are free-living scavengers and predators. A few bad actors besmirch the nematode name by causing human and animal diseases like trichinosis, hookworm, pinworm, and canine heartworm. Most plant parasitic nematodes live in roots and soil, such as the famous root-knot nematode (Meloidogyne species). Pine wilt nematodes are an exception. They don't inhabit the soil at any point in their life cycle and rely on a beetle to carry them around. The story is a bit complicated, but goes something like this…

Monochamus carolinensis,a species of pine sawyer
Natasha Wright, Florida Dept. of Ag. & Consumer Services
Bugwood.org

To get things started, you need a live or recently dead tree or log that is both loaded with pine wood nematodes and infested with one of the longhorn beetles known as pine sawyers. Inside the beetle galleries, the nematodes move into the trachea (breathing tubes) in the sides of the beetle. When the young adult beetles emerge from the wood, their first act is to do what's called a maturation feeding on the bark of healthy conifer twigs. Thus the beetle both carries the nematodes to a new tree and gives them an easy entrance by exposing the wood. There are no recorded instances of the nematodes ever saying "thank you" for this service. Once in the wood, the nematodes mature, reproduce, and colonize their new home. From there, disease progress can be slow or rapid. Tree growth slows down, and needles begin to yellow, wilt, and brown. This can happen on the whole tree or just one branch. Eventually the tree may die. Some of this information - plus the juicy details of the process, involving toxin production and "catastrophic xylem cavitation" - is found in Sinclair & Lyon's book Diseases of Trees and Shrubs, 2nd edition.

Austrian pine (background) and red pine, Wisconsin
USDA Forest Service – North Central Res. Station Archive
Bugwood.org

The astute reader may have noticed something else about the trees pictured above: they aren't native to North America. This is not a coincidence. Although our native pines can become infested by pine wood nematode, most species are not seriously harmed unless they are also under drought stress. The photo at left shows healthy native red pines and pine-wilt-affected Austrian pines in Wisconsin. The native conifers, the pine sawyers, and the nematodes all "grew up together", so to speak. There's been a millennial struggle for the upper hand that's led to a sort of stalemate over the years. Any trees that were too susceptible to the nematodes have died out. Likewise any nematode that could not prosper in the trees didn't survive. We call this process "co-evolution". Newly imported nonnative hosts suffer greatly in this situation, because they never evolved defenses against the local pests. Japanese black pine is a wonderful tree for our coast because of its salt tolerance, but many are lost to pine wilt nematode. Even worse is the situation in Japan and some other parts of Asia. There native pines have been devastated following the introduction of Bursaphelenchus xylophilus.

Sample of Japanese black pine as
received at the NCSU PDIC

If you have a tree that you believe might have pine wilt nematode, contact your County Cooperative Extension Service about sending a sample to the PDIC. Unfortunately, the best sample is rather destructive: a six-inch-long segment of the main stem (2-4" diam), just below the dead terminal. The picture at left shows an excellent sample we received earlier this year. We will forward the material to the NCDA&CS Nematode Assay laboratory. There is no cure for infected trees. The actions you take will be to prevent problems for healthy trees down the road, both literally and figuratively. Trees that test positive should be removed and destroyed. To prevent existing or new beetle infestations from moving the nematodes around, promptly chip the tree. After doing some investigating into the biology of the beetles, our Dr. Chuck Hodges has added the recommendation: "If feasible, it may also help to remove the stump 2-3 inches below ground line." In some quarters the idea seems to have circulated that stumps should be treated with borax. This is actually a practice used to combat annosum root rot - another occasional killer of conifers - but that will do no good against pine wilt. Much more information about pine wilt disease can be found in US Forest Service Publication NA-FR-01-04.