July 15, 2005

Soybean aphids have been seen in some eastern Kentucky counties but none have been discovered in western Kentucky, the state’s primary soybean producing region.

There is little surprise that soybean aphid is in Kentucky because it has been found in the state’s soybean production area every year since its initial discovery in 2000, said Doug Johnson, Extension entomologist with the University of Kentucky College of Agriculture. Nor is the date any particular surprise, although this probably varies with weather, especially temperature, every year.

The insects might not have been discovered yet in western Kentucky but that could be because no one has looked for them, Johnson said. They have been observed in three counties in Tennessee, so Johnson urged farmers to remain watchful.

“That is the key to managing this pest,” he said. “It will be present, but if history is a predictor, it is very unlikely to cause economic damage on full-season beans and fairly unlikely to cause economic damage on any of our beans.”

The beans most at risk are late planted and/or late developing, with full-season bean varieties planted late having the greatest risk of all. The reason these crops are more at risk is that the aphids have to move into Kentucky from northern states because the over-wintering host is either not present or very rare in Kentucky, Johnson said. 

The economic threshold for this pest is an average of 250 aphids per plant during the vegetative stages through reproductive stage “beginning seed.” This is based on a 30-plant-per-field sample and allows for a week to get a treatment on if needed.

“If you are scouting for soybean rust you will want to keep the soybean aphid in mind,” Johnson said. “It will take very little additional effort to look for both.”

The soybean aphid is a native of China but has spread along the western Pacific and is known from Korea to the Philippines. It also has recently been found in Australia. The source of the aphids that began the infestation in North America is not known but they are believed to have been in the United States since the late 1990s.


Editor: Laura Skillman 270-365-7541 ext. 278

Contact: Doug Johnson, 270-365-7541 ext. 214