Weed control and soybean injury from preplant vs. preemergence herbicide applications

Abstract

AbstractPalmer amaranth is one of the most troublesome weeds of soybean in the United States. To effectively control this weed it is necessary to optimize timing of PRE residual herbicides to mitigate Palmer amaranth emergence. Field studies were conducted in 5 site-years to assess the effect of application timing 12 to 16 d prior to planting (preplant) and at planting (PRE) on soybean injury and longevity of Palmer amaranth control using five residual herbicide treatments. A reduction in longevity of Palmer amaranth control was observed when S-metolachlor + metribuzin and flumioxazin + chlorimuron-ethyl were applied preplant vs. PRE in 2 of the 5 site years. Sulfentrazone, sulfentrazone + cloransulam-methyl, and saflufenacil + dimethenamid-P + pyroxasulfone + metribuzin did not reduce longevity of Palmer amaranth control when applied preplant vs. PRE in all 5 site-years. Visible estimates of soybean injury were lower at 21 d after planting when herbicides were applied 12 to 16 d preplant vs. PRE. These findings suggest that preplant applications can be used to reduce the potential for crop injury and may not result in reduced longevity of control when herbicides with a prolonged residual activity are used. Preplant herbicides increase the likelihood of the residuals being activated prior to subsequent weed emergence as opposed to PRE herbicides applied at soybean planting.