April 22, 2009

Since soybean rust was introduced in the fall of 2004 in the United States, Kentucky farmers have seen no yield loss as a result of the disease. However as soybean producers gear up for planting, they should be aware that the U.S. soybean rust distribution map looks significantly different from a year ago, said a plant pathologist in the University of Kentucky College of Agriculture.

"I'm not saying that soybean rust will be a problem this season, but the current location of soybean rust in the U.S. does merit our attention," said Don Hershman, UK extension plant pathologist.

Since 2005, soybean rust has been found in very low levels in the state toward the end of the growing season. By the time it developed, it was too late in the growing season and the state's soybean crop was mature enough that it was not affected by the disease.

However, for the first time, soybean rust has overwintered on kudzu without any break in detection in Alabama, Georgia and Louisiana.

This is an important development for two key reasons. First, these states have very large kudzu populations. Infected kudzu could serve as a springboard for movement of soybean rust to soybeans under the right weather conditions. Also, it is very common for storm systems to originate in the central Gulf area. These storm systems commonly blow up the Mississippi River Valley and into Kentucky.  When there is significant disease activity in the central Deep South, spores of the rust fungus commonly move in high numbers across a broad span of northern production areas.  If this occurs early enough in the growing season, serious crop damage could ensue. Only time will tell what, if any, effects the overwintering has on soybean rust distribution or the 2009 soybean crop.

"The overwinter survival of soybean rust in Alabama, Georgia and Louisiana may have very little or no impact on what transpires during the rest of the season, or it could have a tremendous impact. The determining factor will be the weather conditions over the next two months," Hershman said.

Wet conditions and moderate temperatures favor soybean rust development.

While the disease did overwinter, Hershman said there's been no indication of an increase in disease development despite wet conditions in those states nor has soybean rust been found on soybeans in the Deep South.

 Hershman said it's important for Kentucky growers to at least periodically monitor U.S. soybean rust distribution throughout the growing season. To do so, producers can visit the national soybean rust monitoring Web site, http://www.sbrusa.net/ or UK's soybean rust Web site at http://www.uky.edu/soybeanrust for the latest information. On UK's Web site, growers can register to receive e-mail updates about disease development. They can also call the Kentucky Soybean Promotion Board Soybean Rust toll-free hotline at 888-321-6771.

During the growing season, if a grower suspects soybean rust, they should contact their local UK Cooperative Extension Service office.

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