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Ohio State researcher offers key rust insights from Brazil trip
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3/22/2005 -- WOOSTER, Ohio -- First-hand observations of soybean rust in Brazilian soybean fields are telling Ohio State University plant pathologists one thing: that with diligent scouting, timing of fungicide applications and a blessing from Mother Nature, the disease is easily manageable.
Anne Dorrance, an Ohio State research plant pathologist with the Ohio Agricultural Research and Development Center, was part of an envoy of soybean pathologists and agronomists from across the nation who recently traveled to Brazil to observe the impact of soybean rust on the country’s soybeans. The purpose of the trip was to get a better handle on what U.S. soybean growers might expect from the disease if it spreads northward as anticipated.
“The recurring theme throughout the trip was that the fungicides work,” Dorrance said. “We saw humungous fields in Brazil, and the only place where we could find active rust lesions were in the check plots and in the skips of the sprayers.
“U.S. producers will actually have more resources available than the Brazilians to assist in tracking and monitoring soybean rust, and to assist in the best timing of fungicide applications,” she said.
Soybean rust, an aggressive disease that attacks the crop from the bottom up, was identified in nine U.S. states late last year. Dorrance said the lessons learned in Brazil will help U.S. growers become more knowledgeable regarding the behavior of the disease, preventive maintenance and effective control in the event soybean rust were to continue spreading northward into such states as Kentucky, Ohio and Indiana.
Some take-home tips Dorrance gleaned from the trip to Brazil include:
Timing of fungicide applications is key to limiting losses.
“We are hoping U.S. growers can get away with as few as one application, because it’s going to be the most affordable,” she said. “That being said, the tighter the application window to the appearance of the disease, the best and more effective use growers will get out of that fungicide.”
Each of the three types of fungicides that are available (strobilurin, triazole and chloronitrile) has a certain “shelf life.” The longer the window between application and the disease, the less effective the fungicide is.
Accuracy of fungicide applications is critical to limiting disease development.
“Soybean rust attacks from the bottom up. It’s something we have yet to get a clear sense as to why. It could be because of a physiological aspect of the plant, or it could be because the environment is favorable for disease development,” said Dorrance.
“If you’ve ever walked through a soybean field in the morning," you come out with your pant legs soaking wet, she said. "The dew lasts longer; humidity lasts longer; it’s nice and cool. It’s a very favorable environment for the fungi, and it’s where we need to be looking and where we need to be hitting the applications. And I’m not talking about good coverage or excellent coverage, but outstanding coverage.”
The development and spread of soybean rust is highly weather-dependent.
“One location we visited in Brazil hadn’t had rain for about two weeks. The plants were doing just fine, and under the dry weather conditions, the disease had stopped,” Dorrance said.
From flowering to full seed will be the critical time to protect plants.
“We were finding the disease in Brazil on plants that were in mid-flowering to setting pods. Yet, we really had to dig to find the lesions,” she said. “This is a situation that we may see in Ohio.”
Rust can be a challenge to diagnose.
“Rust lesions look similar to brown spot and downy mildew,” she said. “Only when the lesions began sporulating were we able to diagnose it as soybean rust. When rust begins producing spores, there is nothing else out there like it.”
With luck, Ohio growers may not have to be concerned about diagnosing the disease correctly on their own. Thirty sentinel plots have been set up throughout Ohio to help diagnose soybean rust if and when it first reaches the state.
In the sentinel plots, nearly every leaf will be monitored throughout the season either on a weekly or bi-weekly basis. The first diagnosis of soybean rust in Ohio would most likely come from these sentinel plots, Dorrance said.
The plot system is sponsored by check-off support through the United Soybean Board North Central Soybean Research Program and the Ohio Soybean Council, and is being coordinated by Ohio State University and the Ohio Department of Agriculture.
Source: Ohio State University 3/22/2005 news release, which included this note to editors:
This is part of a periodic series on information regarding soybean rust. The goal is to provide media with the latest updates on the disease and Ohio State’s role in research and education. These updates are expected to continue throughout 2005.
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