Weed control and crop tolerance of micro-encapsulated acetochlor applied sequentially in glyphosate-resistant soybean

Jhala, A. J., Malik, M. S. and Willis, J. B. 2015. Weed control and crop tolerance of micro-encapsulated acetochlor applied sequentially in glyphosate-resistant soybean. Can. J. Plant Sci. 95: 973 981. Acetochlor, an acetamide herbicide, has been used for many years for weed control in several crops, including soybean. Micro-encapsulated acetochlor has been recently registered for preplant (PP), pre-emergence (PRE), and post-emergence (POST) application in soybean in the United States. Information is not available regarding the sequential application of acetochlor for weed control and soybean tolerance. The objectives of this research were to determine the effect of application timing of micro-encapsulated acetochlor applied in tank-mixture with glyphosate in single or sequential applications for weed control in glyphosateresistant soybean, and to determine its impact on soybean injury and yields. Field experiments were conducted at Clay Center, Nebraska, in 2012 and 2013, and at Waverly, Nebraska, in 2013. Acetochlor tank-mixed with glyphosate applied alone PP, PRE, or tank-mixed with flumioxazin, fomesafen, or sulfentrazone plus chlorimuron provided 99% control of common waterhemp, green foxtail, and velvetleaf at 15 d after planting (DAP); however, control declined to 540% at 100 DAP. Acetochlor tank-mixed with glyphosate applied PRE followed by early POST (V2 to V3 stage of soybean) or late POST (V4 to V5 stage) resulted in ]90% control of common waterhemp and green foxtail, reduced weed density to 52 plants m 2 and biomass to 512 g m , and resulted in soybean yields 3775 kg ha . The sequential applications of glyphosate plus acetochlor applied PP followed by early POST or late POST resulted in equivalent weed control to the best herbicide combinations included in this study and soybean yield equivalent to the weed free control. Injury to soybean wasB10% in each of the treatments evaluated. Micro-encapsulated acetochlor can be a good option for soybean growers for controlling grasses and small-seeded broadleaf weeds if applied in a PRE followed by POST herbicide program in tankmixture with herbicides of other modes of action.