Soybean Desiccation by Paraquat, Glyphosate, and Ametryn to Accelerate Harvest1

Abstract

AbstractChemical desiccation is often desirable to hasten maturity so seed can be harvested earlier than normal. Soybeans {Glycine max (L.) Merr.} were sprayed with paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) at 0.6 and 1.1 kg/ha, glyphosphate {N‐(phosphonomethyl) glycine} at 1.7 and 3.4 kg/ha, and ametryn }2‐(ethylamino)‐4‐isopropyl amino‐6‐methythio‐s‐triazine} at 1.1 and 2.2 kg/ha 4, 3, and 2 weeks before the estimated harvest date to desiccate the soybeans and accelerate harvest. The objective was to determine the effect of pre‐harvest chemical desiccation on seed yield and quality. In field experiments, on a fine, montmorillonitic mesic Aquic Arguidoll, Flanagan series soil, harvest was accelerated, but all chemicals significantly reduced yields when they were applied 3 and 4 weeks before harvest. Yields were not significantly reduced by applications 2 weeks before harvest. Paraquat was the most effective desiccant for accelerating soybean harvest. Paraquat also reduced yield and seed weight the most while glyphosate had the least effect. Growth chamber studies indicate that ametryn and paraquat did not affect seed germination or seedling vigor, but all glyphosate applications significantly reduced germination and soybean seedling vigor.Chemical desiccation of soybeans prior to physiological maturity will significantly lower soybean yields. Glyphosate is not recommended as a desiccant.