Investigations of 2,4-d-resistant waterhemp and seed treatment and herbicide interactions in soybean

Abstract

Field research experiments were conducted in 2015 and 2016 in Missouri to determine whether interactions are present between herbicides sprayed prior to planting and seed treatments in soybean. Two varieties of soybean were chosen, one that was known to be tolerant to the herbicides sprayed and one that was known to be sensitive to these herbicides. Each of these soybean varieties were treated with a commonly used seed treatment and sprayed with three commonly used herbicides. The results of these experiments indicate that there were larger interactions present between herbicides and varieties than herbicides and seed treatments or seed treatments and varieties. Greenhouse and field research experiments were conducted in 2015 and 2016 to investigate a waterhemp population with suspected resistance to multiple herbicides including 2,4-D. Results form the field experiment suggested resistance to six of the eight herbicides screened. The only two herbicides that had effective control were dicamba and glufosinate. Greenhouse experiments confirmed the waterhemp population to be resistant to 2,4-D, atrazine, chlorimuron, fomesafen, glyphosate, and mesotrione making this population the third 2,4-D-resistant waterhemp population identified in the U.S., and the first population resistant to six different herbicidal modes of action.