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Digital imaging speeds plant disease diagnosis
MISSISSIPPI STATE – The plant disease diagnostic lab at Mississippi State University handled 726 samples in 2009, and nearly 100 of these were digital images rather than actual samples of diseased plants.
Clarissa Balbalian, diagnostician and lab manager with the MSU Extension Service, said the lab made reasonably confident diagnoses of 75 percent of these digital samples without requiring physical samples.
“That success rate is primarily due to the excellent quality of the photographs and the detailed descriptions that accompanied them,” Balbalian said.
Balbalian has been accepting digital photos for diagnosis for the past seven years, but she saw a definite increase in the number and quality of the images submitted in 2009. Each county Extension office is equipped with a digital camera, and some have microscopes attached to cameras that can be used to submit magnified images of fungal structures.
Stephanie Pendleton, the Extension director for Jackson County, submitted several disease samples last year, many of them digitally.
“When I started this job two years ago, I had samples coming in nearly every day,” Pendleton said. “Instead of mailing them in and my clients having to wait maybe a week to get an answer, Clarissa suggested I use digital photography and e-mail her the images.”
Balbalian advised Pendleton on how to take the photographs to provide the most information for diagnosis. Pendleton said she will sometimes go to the homeowner’s location and take a picture of the whole scene and not just the ailing plant.
“Usually, if I send a picture in and she can see the problem, she will diagnose it from the image,” Pendleton said of Balbalian. “I will send her pictures of blemished fruit, leaves with leaf spot, and ornamental vegetable and landscape problems.”
The lab handled an average number of samples last year, but the wet weather increased the variety of problems and pathogens among the state’s plants.
“The most common disease problem for homeowners was take-all root rot of St. Augustine or centipede grass,” Balbalian said. “Fungal leaf spots were the most common diseases farmers faced, and that was because it was so wet.”
Balbalian said most of the problems she encounters in the lab with grass disease samples are the result of poor home lawn management. She said she expected to see more disease problems with tomatoes because of all the rain, but that did not happen.
“There was a late blight epidemic in the United States with tomatoes and potatoes,” she said. “We never got it in Mississippi, and we searched high and low for it.”
The wet weather did lead to some diseases on the stems of woody ornamentals that Balbalian said are more commonly found on stressed plants in the mid-Atlantic states. Her lab did not handle the soybean rust samples sent in across the state, as these are now handled at MSU’s Delta Research and Extension Center in Stoneville.
When a disease sample comes in, Balbalian said the first thing she does is look at the information provided with the sample.
“It is really crucial that people fill out the form completely or describe in a letter what is going on,” she said. “I need to know the background on this plant. It is especially important because samples often do not look the same after spending a few days in the mail.”
Balbalian identifies the plant first, and then considers the time of year and the diseases commonly affecting the plant. If she rules out common diseases, she starts researching further, calling other experts and running viral tests.
Sometimes identifying the disease is difficult because the correct sample was not sent in.
“We may get a brown leaf or a branch that’s wilted, but the problem is not in the branch. It’s probably belowground, and I can only guess at the issues that are causing it,” Balbalian said. “Other problems are not caused by disease at all but are related to the cultivation of the plant.”
The lab charges $6 per plant disease sample and $11 for a nematode test. There is no fee if the disease can be diagnosed through examination of a digital image.
In addition to the Plant Disease and Nematode Clinic, the MSU Extension Service also offers the Soil Testing Lab as a fee-based service to the residents of Mississippi and nearby states.