Pest Detectives
Perspectives On Line: The Magazine of the College of Agriculture and Life Sciences

NC State University

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Dr. Tom Creswell determines what is ailing a plant. (Photo by Sheri D. Thomas)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stephan consults a guide to verify an insect species. (Photo by Sheri D. Thomas)

 

 

 

 

 

 

 

 

 

 

 

"Pest Detectives":  Scientists with the Plant Disease and Insect Clinic use the latest technology to diagnose crop, garden and home pests --- and more. --- By Dee Shore
Insect identification expert David Stephan checks out a scarab beetle specimen. (Photo by Sheri D. Thomas)

ornate letter W hen it comes to pest samples, Rett Davis imagines he’s seen it all during his 30 years with North Carolina Cooperative Extension: Alamance County people have brought him human lice stuck to Scotch tape; live and dead snakes, spiders and scorpions; moldy carpet; bed bugs; insect-infested meat; poisonous plants and berries; withered leaves; ear wax ... . You name it. Even a pair of panties in a Mason jar.

Many times, the county Extension director is able, on the spot, to tell the afflicted (and the simply curious) just what pest they’ve encountered. Other times, though, he turns to the scientists with the College of Agriculture and Life SciencesPlant Disease and Insect Clinic for help.

“It’s been the single most important tool I use for diagnosing insect and disease problems,” Davis says. “And proper identification is the key to solving these problems.”

The Plant Disease and Insect Clinic, housed in the basement of Williams Hall, has been helping agents and others diagnose pests for more than 50 years. In 1951, Extension set up the clinic amid a devastating Granville wilt outbreak on tobacco. The clinic gradually expanded its services to cover other crops and diseases, adding the insect component in 1970.

Today, the clinic is headed by Dr. Tom Creswell, who handles plant diseases, and David Stephan, an expert in insect identification. They are backed by the help of lab assistant Shawn Butler, along with expertise of specialists from the College of Agriculture and Life Sciences’ departments of Plant Pathology, Entomology, Horticultural Science, Crop Science and Soil Science.

The work of Creswell, Stephan and lab assistant Shawn Butler (left to right) helps Extension agents help their clients. (Photo by Sheri D. Thomas)

Every year, the lab receives between 3,000 and 6,000 samples. Most of the samples come from Extension centers in all 100 counties and on the Cherokee Reservation. Each county is allotted a few free diagnoses a year, but usually a $10 fee is charged per sample. For out-of-state samples and samples that come directly from customers, the fee is higher.

Some samples arrive in cardboard boxes, Ziploc bags and vials of alcohol sent through the mail, while others arrive as digital photographs sent over e-mail.

Computers, digital cameras and the Internet have enabled the clinic to provide its customers with faster answers. And because disease and insect problems can rapidly escalate, saving time often saves money, Creswell says.

Extension’s efforts to speed the diagnostic process got a boost last year, when Drs. Tom Melton and Sterling Southern, department Extension leaders in Plant Pathology and Entomology, respectively, got a $200,000 grant from Golden LEAF. The Long-Term Economic Advancement Foundation, formed in North Carolina as a result of a national tobacco settlement, awarded the grant to help equip 14 county Extension centers with high-quality compound and dissecting microscopes, supplies and computer and imaging equipment that will help them create virtual plant samples.

Whether a sample arrives at the clinic in electronic or physical form, it is logged into a Web-based database before scientists in the clinic begin their work as pest detectives.

Using soil samples, petri-dish cultures and microscopic analysis, Creswell assembles the clues in another plant disease mystery. (Photo by Sheri D. Thomas)

If they can’t immediately identify a plant problem based on the sample’s appearance, then they begin a process of elimination, relying on soil samples, microscopes and petri-dish culture experiments.

Could it be a soil fertility problem? A bacterial disease? A virus? A fungus? Or was the plant subjected to excess pesticides, too little water, too much heat or a hungry insect?

To demonstrate the deductive process the diagnosticians go through, Creswell takes a tomato leaf with a dark greasy spot from a plastic bag.

“ These symptoms suggest a bacterial disease,” he says, laying the leaf on a slip of glass and cutting it with a razor blade before sliding it under the microscope lens.

But immediately he sees tell-tale fungal spores that lead him to a diagnosis of Septoria leaf spot.

Later, he will enter the diagnosis into the Web database, then generate a report that his customer will get through e-mail. These days, about 95 percent of the clinic’s reports are sent electronically, the rest arriving by fax or in the mail.

Each report contains not only the diagnosis but also the recommended treatment.

In some cases, getting the right diagnosis and the right remedy quickly can save companies, especially those in the state’s booming landscape and nursery trade, big money.

In North Carolina, nursery and greenhouse production is the most rapidly growing segment of agriculture, with farm receipts around $1 billion annually.

For some who make their living from the industry, a puzzling condition affecting a relatively new variety of red maple trees this summer was especially worrisome. In June, the Plant Disease and Insect Clinic was lined with containers of maples with shriveled, brown leaves and trunks marked with cankers. The clinic had called in Dr. Colleen Warfield, a plant pathologist, to help pinpoint the problem.

“ We don’t yet know what this is — in some of the samples, it looks like a bacterial disease; in some, a fungus; and some may have cold injury,” Creswell says. “And it may be a complex — a combination of things.

“ Sorting this out is pretty important to the people who have sent us these samples. If I’m wrong about a homeowner’s boxwood, then the homeowner loses a boxwood. But if Colleen’s wrong about the maples, it could have major consequences for our nursery industry.”

Another issue with major consequences that looms on many agricultural officials’ minds these days is bioterrorism, and the clinic is doing its part to help build a stronger national system for detecting and responding to the threat. The clinic is part of the U.S. Department of Agriculture’s National Plant Diagnostic Network, launched recently to enhance national agricultural security by quickly detecting introduced pests and pathogens.

“ The network ties together all the plant clinics in the country, and the information about pests that we are seeing is summarized nationally to see if there are trends that are cause for concern,” Creswell says.

While agriculture and agribusiness are the clinic’s main focus, other industries also benefit. In Alamance County, for example, the clinic helped a local textile industry when an out-of-state upholstery firm rejected its fabric. Upholstery company workers believed that insects at the textile plant had spoiled the fabric, but David Stephan was able to rule that out.

In another case, a truck of shrink-wrapped medical supplies shipped by an Alamance County company was refused entry into Arizona because officials there found what they believed were fire ants. With the help of the clinic, Rett Davis was able to confirm that fire ants had, indeed, gotten into the shipment through wooden packing pallets that came from South Carolina. And, knowing the problem, he was able to offer a remedy that got rid of the ants and helped the company avoid future losses.

Doctors have also called for his help, sending him leaves and berries to determine if they’re harmful to people. And exterminators who encounter out-of-the-ordinary pests have turned to him, too.

Out in tourism-dependent Dare County, agent Susan Ruiz-Evans often turns to the clinic for help resolving insect, turf and landscape problems affecting commercial properties, public athletic fields and even the Cape Hatteras National Seashore.

“ I have 12 years experience diagnosing plants, but I still get stumped sometimes,” she says. “Because we have a minimal operations budget here, we don’t have a (diagnostic) lab set-up at all. So I depend heavily on the clinic -- especially in cases where there’s a commercial concern.”

The clinic not only helps Extension agents crack the stumpers, it also helps them gain knowledge and diagnostic skills that they can use every day. The clinic offers training sessions to agents and Master Gardener volunteers, and Creswell is working to develop a digital image library of plant samples for agents.

“ I’ve found that it’s a tremendous professional development tool — and one of the greatest tools Extension has in working with farmers, landowners, homeowners and others,” Davis says.

“ With the right diagnosis, you can save a crop, a home from wood-destroying pests and protect the environment by preventing unnecessary pesticide treatments. And no one else in the state offers this kind of service.”


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