The risk of damage and yield loss from soybean rust has subsided for crops in the state that are at or past the R5, or beginning seed, stage, according to a University of Kentucky plant pathologist.
"We dodged another bullet this year," said Don Hershman, plant pathologist in the UK College of Agriculture. "Even if spores were to arrive in the state today, it will still take them at least a month to a month-and-a-half to develop, and by that time, all of our soybeans will be made."
He said Kentucky grain farmers may begin to hear about numerous soybean rust discoveries popping up this week in the Deep South. However, this does not translate into an added risk for Kentucky's crop. The new finds likely are the result of spores that were carried by Tropical Storm Fay or some earlier storm system.
Soybean rust was first found in the United States in 2004, and it has had no effect on Kentucky's crop in the past couple of years. The foliar disease was discovered in the state last year, but was isolated to a small number of counties and at extremely low levels. It was hard to find in infected fields last season because so few plants contracted the disease, and the severity of infection for those that did was very low. There were more extensive finds in the state in 2005 and 2006, but in both years, the crop had matured past the stage where soybean rust could cause significant yield loss.
Spores of the rust fungus do not appear to have dispersed as early or as extensively this season as in previous years. This appears to be the result of limited disease development in the Deep South during May through August.
"By this time last year, soybean rust had spread as far north as Arkansas and Oklahoma, but that is not the case this year. I believe we are about three weeks behind where we were this time last year," Hershman said.