Scientists with the Alabama Cooperative Extension System and the state's soybean farmers are preparing to do battle with a new foe, Asian soybean rust. While Asian soybean rust was found on soybeans in 18 Alabama counties last fall, this will be the first planting season that growers have to take the disease into consideration.
Edward Sikora, a plant pathologist with the Alabama Cooperative Extension System, said the disease could be a significant problem if it becomes widespread in the United States.
“Soybean rust may cause significant economic losses to U.S. soybean growers,” he says. “Conservative predictions indicate yield losses of 10 to 15 percent in nearly all the U.S. soybean growing areas with losses up to 50 percent in the Southeast when the disease is not properly managed with fungicides.”
Sikora says some growers are considering using early maturing soybean varieties and planting them earlier than normal as one way to battle the disease.
“Farmers are hoping that by planting early maturing varieties they can raise a crop of beans before the disease reaches their fields,” says Sikora.
Sikora notes there may be problems with that strategy.
“If soil temperatures are too cold or if the weather stays cool, your crop is susceptible to other plant diseases and environmental disorders. Also, if they are growing corn, they may find themselves at harvest time with both crops ready to harvest at the same time.”
He adds that farmers are going to have to take proactive measures to battle the disease successfully.
“Waiting for the disease to show up in your field before initiating your spray program could result in significant yield losses,” says Sikora. “Once an epidemic reaches 10 percent severity, a fungicide application may not be of much benefit.”
Extension scientists and colleagues with the Alabama Agricultural Experiment Station are planting about 25 sentinel plots across the state to monitor the disease's entry and progress this year.
Sikora says the plots are 50 feet by 50 feet in size and will be planted earlier than the conventional planting date for the area with an early maturing soybean variety.
The plots will be checked weekly for the presence of soybean rust.
“This is part of a national program to monitor movement of the disease within the United States,” said Sikora. “The information will be made available through a USDA Web site for use by the public. This information will be vital for successful fungicide management of soybean rust by our growers as well as soybean growers in neighboring states.”
Soybean rust can be managed with the judicious use of fungicides. Fungicide applications can reduce yield loss, depending on the plant's developmental stage, time when soybean rust is detected, and fungicide application method.
Sikora says the timing of the first fungicide application is critical. Applications should begin at flowering when the threat of the disease is considered high for an area. Subsequent applications should be made 14 to 21 days apart, depending on the product used.
“The fungicides will raise producer costs by some estimates as much as $20 to $30 dollars per acre,” says Bob Goodman, an Extension agricultural economist. “Lots of farmers who planted soybeans last year may be reevaluating if they will plant beans this year. They should also be looking at all their production practices critically to insure they are using the most cost effective means of operation.”
Sikora notes that the disease is caused by the fungus, Phakopsora pachyrhizi.
“The fungus, which requires living tissue to survive, did not over-winter in Alabama. But viable spores have been found on kudzu leaves in two Florida counties. This indicates the disease survived the winter in Florida. It's only a matter of time before we see it on kudzu and other host plants in Alabama.”
All commercial varieties of soybeans currently available are highly susceptible to the disease.
The USDA recently launched a Web site, www.usda.gov/soybeanrust. From this page, you can link to the USDA Public Soybean Rust website, www.sbrusa.net. This site contains maps for observations, recommendations, and scouting information controlled by state soybean specialists.
Sikora also recommends another Web site that offers a comprehensive look at the disease as well information on identification and management of the disease.
“The American Phytopathological Society, the Plant Management Network, and other scientific organizations have launched an online soybean rust center at www.plantmanagementnetwork.org/infocenter,” says Sikora. “It offers breaking news on soybean rust, links to featured soybean rust sites, and information on the identification and management of soybean rust as well as links to university and Extension sites.”