When Soybean Rust Hits

Steps to take if you expect soybean rust is in your field. Jacqui Fatka

Published on: May 21, 2004

Soybean rust will most likely show up in the United States. Since it is a matter of when, not if, researchers are asking growers to help the U.S. stay ahead of the curve by finding the disease early.

Jim Peters, brand manager for Syngenta fungicides, says he believes the probability of the disease arriving in Minnesota is as high as it is in Mississippi. "It's going to be here, and we're going to be ready for it," he says.

The best way to fight the disease is treating it early. Peters says he is concerned there is a lack of scouting and the disease is hard to detect. "Drive by scouting will not be enough to get the early diagnosis needed to stay ahead of it. If you can see it from the road, it's way too late," he says.

Glen Hartman, research plant pathologist for USDA and associate professor at the University of Illinois, says that many states have specialized scouting plans. For instance Florida's Department of Agriculture is conducting additional scouting since the wind-borne disease will likely hit near there first.

Soybeans begin to undergo their reproductive stage around the Fourth of July weekend. "This is a key time to take a look around and identify what's there and what's present," Peters says. "For that couple of week window I'd be out there and walking around every so many days assessing the situation."

The rust first appears in the lower canopy. Soybean rust forms two types of lesions on leaves, tan and reddish brown. The tan lesions when mature, consist of small pustules with masses of tan colored spores on the surface. To view pictures, click HERE.

Allison Tally, Syngenta technical brand manager, says that producers should take several leaf samples from the lower canopy and look at them under a 20x lens to take a close look at whether it is soybean rust.

Suspect samples should be sent to state labs

If leaves resemble the characteristics of soybean rust, producers are asked to place the leaf, stem, or pod samples in a self locking plastic bag and store under cool conditions. Alternatively, samples that must be kept under ambient conditions should be sealed in a paper bag to prevent mold growth. Once they can be refrigerated the paper bag can be placed in a self locking plastic bag. It would be helpful if leaves can be placed between paper towels or pieces of paper to keep them flat. Care should be taken to ensure the outside of the bags are not contaminated by the sample.

Record the collection information (date, exact location of the field and sample location within the field, county in which collected, host plant and collector’s name and phone number) on a piece of paper included with the sample. Hartman adds that the producer should get the sample to the state diagnostic lab immediately either by FedEx or taking it in person.

For more information on submission procedures, click HERE. (This is link requires Adobe Acrobat Reader. For a free download, go to http://www.adobe.com/products/acrobat/readstep2.html.)

Methods of control

Several U.S. chemical companies have fungicides that significantly reduce the harmful effect soybean rust can have on yields. Early application remains key.

Tally says that in Syngenta trials in Brazil, if the disease is less than 10% in the lower canopy and the mid-canopy has less than 5% one application of its Tilt may be enough for the entire season. If the disease is more than 20% in the lower and 10% in the mid-canopy, she would definitely recommend a second application in a 14-day interval.

Treatment would cost approximately $12-$13 per acre. "On top of that would be costs association with applying," Peters explains. Bringing a realistic bill to $20 per acre. He adds that each application would cost $20. If a single application was applied early when the disease was at low levels, the timing could increase the yield by nine to 12 bushels. If producers waited and applied fungicide when the rust was at 13% in the lower canopy, they would see a five bushel increase in yields. With 30% coverage, only three bushels would be added to the yield, making the treatment less economical.

Additional Resources

APHIS Soybean Rust Resource Page

Soybean Rust Infected Soybean Plant Photos 

Early Symptoms of Soybean Rust

Diagnostic Characters for Soybean Rust Identification

Collection and Submission of Samples