Sulfentrazone enhances weed control of glyphosate in glyphosate-resistant soybean (Glycine max)

Field studies were conducted from 1998 to 2000 at Belleville, IL, to evaluate tolerance and weed control in glyphosate-resistant soybean with sulfentrazone application. Sulfentrazone alone caused 14 to 16% height reduction 14 d after treatment (DAT), and sulfentrazone plus chlorimuron caused 26% height reduction 14 DAT. Minimal height reduction (0 to 11%) was observed 56 DAT. Sulfentrazone alone controlled giant foxtail 97 to 100%, yellow nutsedge 96 to 98%, common waterhemp 97 to 98%, common cocklebur 91 to 94%, and ivyleaf morningglory 100%. Sulfentrazone alone controlled common ragweed 63 to 89% and giant ragweed 50 to 72%. Sulfentrazone plus chlorimuron or cloransulam increased control of common and giant ragweed to 95% or greater. Sulfentrazone followed by glyphosate increased control of yellow nutsedge, common waterhemp, and ivyleaf morningglory compared with a single application of glyphosate. Sequential applications of glyphosate controlled weeds 93 to 100%. Sulfentrazone plus chlorimuron or cloransulam postponed the application of glyphosate at the 10-cm weed height by 12 d. Despite the injury, sulfentrazone did not reduce grain yield. Inadequate giant ragweed control reduced grain yield by approximately 48%.