Herbicide Programs for Controlling Glyphosate-Resistant Johnsongrass (Sorghum halepense) in Glufosinate-Resistant Soybean

Three field experiments were conducted in 2010 and 2012 in a soybean production field near West Memphis, AR, containing glyphosate-resistant johnsongrass. The goal of this research was to develop effective herbicide programs for glyphosate-resistant johnsongrass in glufosinate-resistant soybean. Control of the resistant johnsongrass was greater with glufosinate at 590 and 740 g ai ha(-1) than at 450 g ha(-1). Sequential glufosinate applications were more effective than a single application, irrespective of rate. A PRE application of flumioxazin at 71 g ai ha(-1) immediately after planting provided no more than 26% johnsongrass control 6 wk after soybean emergence (WAE). The addition of clethodim at 136 g ai ha(-1) to sequential applications of glufosinate at 450 g ha(-1) improved control over sequentially applied glufosinate alone. Herbicide programs containing imazethapyr or imazamox in combination with glufosinate followed by clethodim plus glufosinate controlled johnsongrass at least 94% at 10 WAE and provided three distinct mechanisms of action, a highly effective resistance management strategy. Results from this research indicate that a high level of glyphosate-resistant johnsongrass control can be achieved through the use of several herbicide options in glufosinate-resistant soybean.