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Soybean rust may not require fungicides
MISSISSIPPI STATE -- Mississippi State University Extension Service specialists are hopeful that incidences of soybean rust across the state will continue to be minor and only occur after plants have passed the at-risk growth stage.
Tom Allen, Extension plant pathologist at the Delta Research and Extension Center in Stoneville, said the disease was first detected in the state on Aug. 6 in Holmes County. Within the next couple of weeks, isolated spots were found in additional counties including Bolivar, Carroll, Grenada, Humphreys, Issaquena, Leflore, Montgomery, Sharkey, Sunflower, Warren, Washington, Yalobusha and Yazoo. More findings are expected.
“At this time we have not seen a case where the use of fungicides has been needed,” Allen said. “In most cases, soybean rust was detected on soybeans that were beyond the growth stage (R5.7) when rust could cause yield reductions.”
Allen said if growers with later soybeans are already planning to make an R3/R4 fungicide application, they should consider a pre-mix or tank-mix of strobilurin/triazole to help prevent rust or apply a strobilurin fungicide to prevent rust and provide a yield increase if the yield potential appears to be good.
“Producers should know that if an infection has occurred, a strobilurin application will only prevent further infection and will not ‘cure’ the disease,” he said.
Extension soybean specialist Trey Koger said detecting soybean rust is difficult. Many other soybean diseases have symptoms that look similar to rust. The key to confirming rust is using a magnifying lens to find pustules on the undersides of soybean or kudzu leaves.
“The good news is that the majority of the state’s soybeans are very close to maturity. Probably 70 percent of our soybeans are out of the woods,” he said. “In many areas, lack of rain is a bigger concern than soybean rust.”
Koger said Mississippi growers have been fortunate that soybean rust has not impacted yields since it was first detected in the state six years ago.
“We have not lost one bushel of soybeans in the state of Mississippi to soybean rust,” he said. “The 2009 crop is more at risk than those in previous years because it’s a later crop, but the good news is it’s growing very fast and quickly getting to the stages where it is not vulnerable to rust.”
The MSU Extension Service has a Soybean Rust Scouting team that examines the state’s 20 sentinel plots, kudzu stands and commercial fields for soybean rust each week. These scouts began their work in March and will continue until soybeans are harvested. The information they gather is used each year to make management or treatment recommendations anytime rust is detected in the state.
Call the Soybean Rust Hotline at (866) 641-1847 for up-to-date information about soybean rust in Mississippi, Arkansas or Louisiana. The hotline is made possible through the Mississippi Soybean Promotion Board and BASF.