The hot, dry weather that has dogged the upper Southeast since mid-April appears to have at least one silver lining — the threat of soybean rust is just about gone and an additional diagnostic tool is coming online to give Southeastern growers even more tools to avoid rust damage in the future.
Veteran Asian soybean rust chaser John Mueller comes just short of saying the risk for Asian soybean rust is over for 2010, but does point out that the intense summer heat and dry weather and severe winter weather has pushed the disease organism farther south than in recent years.
Speaking at a recent field day Mueller said, “For the past five years we’ve been concerned that Asian soybean rust would come into South Carolina and be a big problem for us. Based on that threat we have developed a monitoring system (sentinel plots) that can detect infection on one leaf out of a hundred in one of these plots and we’re now able to give growers a 2-3 week notice of when they need to spray.
“This year we’ve had one of the consistently coldest winters we’ve ever had — even down into Mexico where some of our rust over-winters. Because of that the live hosts needed for rust to over-winter were killed off in the winter.
“The end-result is rust is really late developing this year. Typically, we pick up our first rust in our sentinel plots from Aug. 15 to Sept. 15. By Aug. 15, the closest rust to South Carolina is in the Florida Panhandle and barring the perfect storm — some combination of hurricanes or tropical storms, it’s not likely to get here in time to do any damage to our soybeans, Mueller says”
Some growers are getting excited about rust-like yellowing on soybean leaves. Mueller, who is also director of Clemson’s Edisto Agricultural Research and Extension Center in Blackville, S.C., explains the yellowing is downy mildew coming in as soybeans begin to flower. Downy mildew is typical and not likely to cause a lot of yield loss, he says.