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Soybean research works to control plant diseases
MISSISSIPPI STATE -- Asian rust began demanding the attention of soybean growers across the South last year, but it is not the only disease producers must consider when growing the crop.
Soybeans began to receive more attention in the late 1980s when average yields finally rose above the low 20 bushels an acre mark. Mississippi State University research and support of the industry, funded in part by the Soybean Promotion Board, was largely responsible.
"There is a cooperative spirit in Mississippi and the South between our research counterparts and growers," said Alan Blaine, soybean specialist with the MSU Extension Service. "We appreciate the opportunity to expand our knowledge base and pass this on to producers."
Gabe Sciumbato, plant pathologist with the Mississippi Agricultural and Forestry Experiment Station, researches soybean diseases at the Delta Research and Extension Center in Stoneville.
"I test varieties for several diseases that are of importance to soybeans to see if the varieties are susceptible," Sciumbato said. "Among the diseases we test are stem canker, frogeye leafspot, purple leaf stain and charcoal rot."
There were more than 300 entries in the MSU soybean variety trials in 2005. Varieties are resistant to different diseases, and Sciumbato said producers need to know before planting what different varieties can withstand and what they cannot. Producers who know their fields are prone to getting a particular disease can select a variety that expresses resistance to that disease.
Sciumbato said he and others are working on the control of late-season foliar diseases that cause yield losses.
"We're evaluating fungicides that are sprayed at the R3 reproduction stage. We found we can increase average yields by four to six bushels an acre by spraying the proper fungicide at this point," Sciumbato said. "We've shown the use of fungicides to be consistently profitable on irrigated and high-yield potential soybeans grown in monoculture or in rotation with rice. Future efforts will focus on non-irrigated production systems and other rotation scenarios."
Seed treatments is another area that has experienced significant growth.
"When you plant early like we're doing, a couple of fungi can cause some real losses on clay soils that are poorly drained in cold weather," Sciumbato said. "We went from using no seed treatments to practically 100 percent seed treatments when we made the switch to early planting, and they've made a night and day difference."
Sciumbato said charcoal rot regularly is the No. 1 soybean disease, and a lot of attention has been focused on its control. Researchers have isolated the toxin the fungus produces, and all varieties have been screened for resistance to this toxin. Sciumbato said all soybeans in the state are infected with this disease within the first five weeks after planting.
"If the weather is good, it never affects the plant, but if the plant is stressed, the disease gets a foothold," Sciumbato said.
Asian rust charged into high priority when it was discovered in the United States in 2004. Alan Henn, Extension plant pathologist, said the U.S. Department of Agriculture had been working on the disease since the 1970s in anticipation of its arrival.
"After 9/11, there was concern about agricultural bioterrorism, and Congress classified soybean rust as one of nine select agents which bioterrorists could use to harm U.S. production," Henn said. "Through the national plant diagnostic network, we started training people to look for, identify and report rust and these other agents."
When this training began, Henn also sought special use exemptions that would allow effective fungicides to be used against rust. The triazole class of chemicals was found to be most effective after rust exposure, and the strobilurin class provides the best barrier to infection.
"The fungicides had to be easily available and in sufficient quantities that the soybean industry throughout the United States could rely on their availability," Henn said. "The approval was made prior to the find, and activated on the day of the find."
Dan Poston, a MAFES researcher who also works in Stoneville, said some of the fungicides labeled for use against rust will also be effective in the fight against other fungal diseases.
"Before rust showed up, we learned what impact these fungicides will have on yield. That's been an extremely important data set, and we were able to use that information to build a rust program around these chemicals."
By fine-tuning application timing, researchers have shown that the proper fungicides applied correctly can provide disease protection and break-even on cost or even make a profit.
Contact: Dr. Gabe Sciumbato, (662) 686-3221