Be Sample Savvy

Five Steps to a Successful Plant Disease Sample

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Submitting a soybean disease sample? Go ahead and send the whole plant if possible, plant diagnosticians say. (DTN/The Progressive Farmer photo by Gregg Hillyer)

ROCKVILLE, Md. (DTN) -- Have you ever thought about how hot the back of a mail delivery truck gets? Or the dashboard of your pickup truck after a day in the sun?

Suzanne Bissonnette knows.

The director of the University of Illinois Plant Clinic has seen crop samples take some serious heat before they reach her desk.

"If someone takes some diseased corn leaves and puts them on the seat of a truck or a dashboard and cooks them in 120-degree-Fahrenheit heat for a few days, they've essentially sterilized it," she said. "We may still be able to see the symptomology of the infection but not isolate the pathogen."

Foliar diseases are racing through many corn and soybean fields this month, and the samples are starting to wing their way to diagnostic labs around the country. Here are some tips to make sure yours survive the journey.


That disease is your enemy, yes, but treat it nicely, please.

"It's kind of backwards, but what we're really trying to do is keep the pathogen alive long enough for us to diagnose it," Bissonnette said. "Having fresh material with an active infection and pathogen still alive is so important."

A rotted sample turns into a pathogen free-for-all, added Adriana Murillo-Williams, an Extension educator with Penn State University Extension.

"When a plant dies, many other pathogens are waiting there, ready to invade and it becomes impossible to tell which one caused death," she explained.

To preserve your sample, keep it as dry as possible. "Plastic baggies are not always your friend," Bissonnette noted. The plastic can trap heat and moisture, so if you're using one, add a dry paper towel to the bag, she said.

Better yet, skip the plastic and go with newspaper. "Leaves wrapped in newspaper work just fine," Bissonnette said.

Some samples, such as roots with potential nematode infestations, must be kept cool. Bissonnette recommends using blue freezer packs -- not plastic bags filled with ice. "Ice in Ziploc bags melts and you get a soupy mess," she said.


Getting small snippets of diseased leaves or just a few affected corn kernels is not ideal, Murillo-Williams said.

"It sounds strange, but what we really need is healthy tissue, as well as plant tissue with a range of symptoms, from mild to severe," she said. For example, it's best to send entire ears of corn when you suspect ear rots, she said.

While you're at it, consider sending an entire plant, Bissonnette said. Maybe it's the wilted leaf you're worried about, but it could be a root rot causing the problem.

"If you're trained in disease symptomology, then you can probably get away with sending in fewer parts, but otherwise, your best bet is to send a whole plant, particularly for field crops, where you can easily spare one whole plant," Bissonnette said.

If you specifically want roots analyzed, it helps to send an intact root ball, soil and all, Murillo-Williams said. She recommends using Styrofoam cups to hold the sample. Even just a bag wrapped around the roots and soil and secured at the stem will work, added Bissonnette.


Most clinics provide a form for you to fill out for each sample. Please don't ignore it.

"We get everything from palm trees in a conservatory to the latest soybean variety," Bissonnette said. "We can't push a button and know exactly what plant this is, what variety and how it was grown."

Take the time to provide critical details such as the variety, growth stage, field history, recent weather, symptomology patterns, and chemical, nutrient and fertilizer use. "This is really the bare minimum of what we need," Bissonnette said. (See an example from Illinois's plant diagnostic clinic here:…)

Bissonnette also encourages growers to send in digital pictures to the clinic's email address, as long as you take care to identify which physical sample they go with. Pictures of a pattern in the field and other affected plants can help diagnosticians immensely -- but only if they are clear.

"Believe it or not, the Internet doesn't make a fuzzy image any clearer," she said.


"Take into consideration what the plant will go through getting to the clinic," Bissonnette urged.

Shipping can involve hot delivery trucks, multiple changes of hands and long waits in mail sorting rooms.

As a result, many commercial ag businesses and local farmers deliver samples in person, which is the best option, if possible, Bissonnette said.

If you have to rely on shipping, Bissonnette and Murillo-Williams recommend mailing samples overnight, early in the week.

"A lot of public diagnostic clinics are located on university campuses, and we do not get delivery on Saturday, so you can have them sitting at the post office or FedEx or UPS until Monday," Bissonnette said.


Penn State's Plant Disease Clinic is one of only a handful of labs in the country that offer free plant diagnostics, Murillo-Williams said.

Most university plant diagnostic clinics do charge fees. The Illinois plant clinic's fees range from $18 to $120, depending on the type of tests you want run, Bissonnette said.

You can find fee listings on a plant disease clinic's website. (See, for example, the Illinois clinic's list here:…).

Check also to see what tests your plant clinic of choice can run. For example, the Illinois plant clinic does molecular assays for herbicide resistance, analyzes nematodes and does Hg and SCN typing in addition to traditional disease testing.

Penn State's clinic doesn't test for viruses or nematodes, but they will redirect samples damaged by insects or nutrient deficiencies to the appropriate ID services, Murillo-Williams said.

To learn more about the plant diagnostic clinic in your state, see the National Plant Diagnostic Network here:….

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Emily Unglesbee