So far in 2008, Asian soybean rust discoveries have been limited to states along the Gulf of Mexico with most of the confirmed finds in Florida. Only a few counties in Alabama, Louisiana, and Texas have seen soybean rust, unlike last year when hundreds of counties in more than a dozen states found the disease.
Hot, dry weather in the Southeast has kept spores bottled up, but with tropical storm season here, wet conditions are conducive for spore development and rains and winds can rapidly carry spores hundreds of miles. Earlier this week, spores were discovered in a couple of counties in Georgia and with the wet weather, growers in the Carolinas, Tennessee, Alabama and Mississippi need to be wary and ready to apply fungicides to late-planted soybean crops.
In the past, by the time soybean rust reached Midwestern states, soybeans were in advanced growth stages so rust was not a problem, but because of the floods and wet spring, crops are maturing later and rust could spell yield losses. In particular danger this year is Missouri, where most of the 5.3 million acres of soybeans were planted as much as a month behind schedule.
"This year we have late-planted full season soybeans, and then of course we have some double-crop soybeans and even some of those were planted pretty late," says University of Missouri agronomist Bill Wiebold. "So we have some soybeans that will enter into September that are pretty young and those would be vulnerable to a late season influx of rust spores."
The usual pathway rust takes to the Midwest is through Louisiana and Texas, and until recently those areas have been extremely dry. Earlier this year Hurricane Dolly dropped a lot of rain in Texas and moved north into the Midwest, but according to Wiebold didn't bring rust. However; the move inland of the tropical storm Fay could bring rust to the Midwest depending on the air current patterns.
"Now that we're into what looks like an active hurricane season, we have to keep an eye on what's happening in those southern states." Wiebold says. "They are kind of our sentinel plots and as we watch that we'll get an idea of whether we should be concerned or not.