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Sudden death more likely than rust Tuesday, July 19, 2005
Agri News staff writer
WASECA, Minn. -- It's unlikely soybean rust will cause a problem in Minnesota this year, says a University of Minnesota soybean pathologist.
Jim Kurle, with the University of Minnesota Department of Plant Pathology, says it's more likely that there will be sudden death syndrome and charcoal rot than rust this year because of the cold, wet spring and the hot, dry July.
The weather has set soybeans up for a lot of diseases, Kurle said, speaking at last week's Disease and Insect Field Tour at Southern Research and Outreach Center in Waseca.
In order for rust to develop in Minnesota, environmental conditions must be right when the wind blows spores northward.
Those environmental conditions include six hours of leaf wetness, humidity ranging from 75 percent to 80 percent and temperatures ranging from 59 degrees to 82 degrees. In a 30-year period, those conditions exist about two-thirds of the time in southeastern Minnesota and about one-third of the time in western Minnesota, Kurle said.
Rust is spreading slowly through the southern United States, he said, with infestations reported on soybeans in Florida, Georgia and Alabama. Rust over wintered on kudzu in Florida. It must have a living host to survive the winter, Kurle said. Favorable conditions for this exist only along the Gulf Coast. As a result, every year will be different in Minnesota and the state's soybean growers start from a clean slate each spring.
The slow spread of rust this year makes sense because it had been hot and dry in the southern states until Hurricane Emily blew ashore and dumped several inches of rain.
Kurle predicts soybean rust will move northward from Texas and Louisiana to Minnesota along the Puccinia Pathway in much the same way as small grain rust.
Experts aren't taking any chances that rust will sneak up on them.
A nationwide network of sentinel plots, including 36 in Minnesota, allows soybeans to be monitored closely for signs of rust. The map showing infested counties is updated weekly on the Internet.
Farmers who are scouting for rust are seeing other diseases, including frogeye leaf spot, septoria brown spot, downy mildew and bacterial blight.
When scouting for rust, check early planted fields with early maturing varieties first. It's also good to check fields with early canopy closure and low-lying fields or protected fields that tend to have more dew. Examine the lower plant leaves with a hand lens.
The lesions look a little like volcanos, said regional Extension educator Lisa Behnken, and it's possible to see the volcanos erupt and spores coming out.
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