After a few weeks of consistently wet weather, soybean rust is making its annual march from the Gulf Coast to north Alabama. Spurred on by wet leaves and strong winds, the fungal disease popped up in 33 of Alabama’s 67 counties. Alabama Extension specialist Dr. Dennis Delaney weighed in on the development and offered advice to soybean farmers across the state.
“Some fields look great, and some look terrible. It’s all over the board,” Delaney said. “This bout of rust is about average, but with wet weather, it’s spreading more quickly than usual.”
Delaney explained that each year rust sweeps from the more humid coast to the northern part of the state. “Soybean rust is an annual issue,” he said. “It’s a matter of when it moves in. If it moves in during early fall, most soybeans are already out of danger.”
Soybean rust affects the leaves of the plants, which provide nutrients for the developing soybean pods. If the plants are beyond the R5 growth stage–– past the point of seed development–– soybean rust is harmless and dies when cold weather arrives later in the year. If it arrives in the late summer, it can present problems. Farmers have some ways to fight back, but they must act quickly.
What can be done?
“The only really good controls we have for soybean rust are fungicides,” Delaney said. “They are mainly preventative, and if you hear there is rust in your area, you often need to spray your fields.” Once the soybean rust has developed, it is much harder to control.
Many farmers in north Alabama do not spray their fields for soybean rust annually, he said. On the coast, meanwhile, it’s usually a good idea to spray most summers. Most fungicides control a variety of fungal diseases, and soybean rust is usually among them. Delaney stressed that farmers must consider economics when choosing whether or not to spray.
“Farmers must decide if their yield projections are high enough for the fungicide to be an economical choice,” he said. “There are no forecasts for damage out yet, but soybean rust can often result in a 30 percent yield loss. For most farmers, spraying is going to be an economical choice this year, but it is always case-by-case.”
Dr. Ed Sikora, an Alabama Extension plant pathologist, also advised spraying for soybean rust. “Growers should be advised to consider a fungicide application this year, particularly a product with both protective and curative activity,” he said. Using a curative fungicide could help farmers who are already seeing rust in their fields.
Another solution is planting early. If farmers plant soybeans in the early part of the season, they will often mature before the wave of soybean rust can reach them.
(bottom right) Soybean leaves infected with ASR/by USDA – http://www.ars.usda.gov/is/espanol/pr/2009/090326.es.htm, Public Domain, Link
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