Sensitivity and Likelihood of Residual Herbicide Carryover to Cover Crops

Abstract Research was conducted to evaluate the sensitivity of cover crops to a low rate of soil-applied herbicides and investigate the likelihood of herbicide carryover to fall-seeded cover crops following an irrigated corn crop. In the sensitivity study, herbicides were applied at a 1/16×rate (to simulate four half-lives) 1 d after cover crop planting, whereas for the carryover study residual herbicides were applied at a 2×rate at the maximum label corn height or growth stage and cover crops sown immediately after corn harvest. In the sensitivity experiment, atrazine, diuron, fluridone, fomesafen, metribuzin, pyrithiobac, and sulfentrazone reduced emergence of the leguminous cover crops Austrian winterpea, crimson clover, and hairy vetch. However, reduced biomass production of leguminous cover crops in the spring was only observed for atrazine, fluridone, and pyrithiobac. For rapeseed, atrazine, flumioxazin, fluridone, pyrithiobac, pyroxasulfone, sulfentrazone, and tembotrione reduced emergence, but biomass production was reduced only by atrazine and fluridone. Conversely, wheat, cereal rye, barley, oats, and triticale were not affected by soil-applied herbicides. Barley was the only cereal cover crop that showed biomass reduction due to the application of flumioxazin, fluridone, mesotrione, S- metalochlor, and sulfentrazone. In the carryover study, with the exception of crimson clover, Austrian winterpea, cereal rye, hairy vetch, rapeseed, and wheat showed no negative affect on biomass production following a 2×rate of postemergence-applied residual herbicide in corn.