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Corn+Soybean Digest

Trained For Triage

First detectors are the paramedics of the soybean rust world. If you've got something suspicious in your field, your first call should be to a first detector. He or she will tell you if what you have is really something more benign, like septoria leaf spot, or if you should send your sample to a lab for tests.

First detectors are the brainchild of the National Plant Diagnostic Network (NPDN) and serve as its eyes and ears. The First Detector Program is the first widespread effort by NPDN to train a large group of people to be on the lookout for an exotic pest, says Coanne O'Hearn, national survey coordinator for USDA/APHIS/PPQ.

Approximately 10,000 people have received first detector training, says William Hoffman, program specialist for the Cooperative State Research, Education and Extension Service (CSREES).

“During the first round of training we tried to get every Extension agent — nearly one in every county in the U.S. — trained to recognize rust,” says O'Hearn. “Private ag firms, industry reps and crop consultants have also been trained.”

Jim Kurle, University of Minnesota plant pathologist, says: “The goal is to train a lot of people so they know what they're looking for in the field. We want to determine what is soybean rust and what isn't so we don't overrun testing labs.”

Spotting soybean rust requires scouting and a good hand lens. Everyone's eyes are different, so choose a lens that works for you, says Kurle. Some people prefer a 10 or a 20x lens, while others prefer 50x. Soybean rust starts as small lesions on the undersides of the lower leaves of the soybean plant.

“It's easy to tell that it's soybean rust after the lesions have produced spores. But once they've produced spores, it's almost too late. You need to treat the disease early, before the lesions form spores.”

Kurle recommends that you scout for rust at least twice a week. If it has been found near you, scout every other day.

Scouting for rust isn't like scouting for any other soybean pest, says Kurle. In fact, experts in Brazil recommend farmers scout spots most likely to get rust first rather than the entire field, he says, explaining that farmers know where they have cooler, wetter spots and that's where rust is likely to form first.

Soybean rust needs moisture to form. It takes a minimum of six hours of leaf wetness to cause infection. Ideal temperatures for the disease are between 60-85°F.

If you and a first detector agree that your field may have rust, here's what to do:

First, collect the sample. Place about 20 symptomatic leaves between layers of dry paper towels or newspaper in a plastic bag. Don't add extra water to your sample.

“For rust we are asking people to double-bag their samples. Be sure to label each sample clearly with a permanent marker. Include information such as location of the field (county and township), location of plant in the field (GPS coordinates, if you can), soil type, weather conditions, cropping history and tillage practices,” says Sandee Gould, director of the University of Minnesota plant disease clinic.

“Remember — dead plants don't work. The accuracy of the diagnosis is only as good as the sample you submit,” she says.

Lastly, mail the package in a crush-proof box, not an envelope, says Gould. If you can, mail it early in the week or ship overnight to avoid weekend delivery.

A farmer can perform a field test by placing several suspect leaves in a plastic bag. Breathe into the bag to increase the humidity and seal it, says Gould. If it's rust, the lesions should form pustules or spores within 24-48 hours, she says.

“It's important to use the first detectors,” says Gould. “We want you to send in a sample, but we don't want you to skip steps in the process.” Samples help researchers track the movement of disease, she says.

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