Control of Glyphosate-Resistant and Glyphosate-Sensitive Giant Ragweed in Soybean with Adjuvant, Fomesafen, and Glyphosate Tank Mixtures

Field research was conducted to determine the effectiveness of glyphosate, fomesafen, and adjuvant combinations on 6-inch glyphosate-resistant (GR) and 12-inch glyphosate-sensitive (GS) giant ragweed. Glyphosate alone controlled GS giant ragweed greater than 93%, but control of GR giant ragweed was less than 47%. GS and GR giant ragweed responded similarly to fomesafen as control ranged from 42 to 86%. Control with reduced rates of fomesafen was enhanced with additional adjuvants. Regardless of adjuvant, the labeled use rate of fomesafen alone at 0.352 lb/acre provided 75 to 86% control of both GR and GS giant ragweed. The addition of glyphosate to fomesafen resulted in over 90% control of GS giant ragweed. The addition of glyphosate to fomesafen did not improve control of GR giant ragweed and when additional adjuvants were not used, control was reduced when glyphosate was added to 0.352 lb/acre of fomesafen.