With soybean planting proceeding at a rapid pace, University of Illinois Extension weed specialist Aaron Hager says there's a great likelihood fields were planted before soil-residual herbicides could be applied.

"If soybean have not yet emerged, it is possible that the application could proceed as originally planned," Hager says. "However, if a certain number of days have elapsed since planting or if soybean have begun to emerge, proceeding with the planned application is dependent upon the respective herbicide."

Only a few herbicides that are most frequently applied before soybean planting or emergence can be applied after the soybean have begun to emerge. Several soybean herbicide active ingredients can cause severe soybean injury if applied directly to the soybean plant, or if applied close to soybean emergence.

"Labels often restrict applications to within a certain number of days after planting and/or before there are any visible signs of soybean emergence," Hager adds. "Keep in mind that, in general, the potential for soybean injury can increase as the interval between application and planting decreases."

In addition, environmental factors such as timing of precipitation in relation to herbicide application and soybean planting or emergence, and crop genetics also influence the potential for soybean injury. 

According to Hager, not all soil-residual soybean herbicides can be applied after soybean emergence will control emerged weeds so additional management procedures such as adding a herbicide with postemergence activity may be needed in situations where weeds also have emerged.

"Always consult product labels for additional information, such as the need for tank-mix partners or spray additives to improve control of existing weeds," he says.

For more information on postemergence applications of the more traditional soil-applied soybean herbicides, read the May 26 edition of The Bulletin at http://bulletin.ipm.illinois.edu/.

In addition, the U of I Weed Science Field Day is scheduled for June 29 at the Crop Science s Research and Education Center in Urbana. Contact your local Extension office for more information.