Competition of Jimsonweed with Soybean¹

Abstract

Abstract Jimsonweed ( Datura stramonium L.) is a broadleaf weed that has become increasingly severe in Midwest soybean ( Glycine max (L.) Merr.) fields (9, 14). Knowledge of the competitive effects of this weed with soybean would be helpful in developing production practices to minimize losses. Our objectives were to determine the response of soybean (cv. Wells) stand and seed yield to (a) various jimsonweed densities, (b) different emergence dates of jimsonweed, and (c) various durations of jimsonweed competition and to compare the effectiveness of bentazon [3‐isopropyl‐1 H ‐2,1,3‐benzothiadiazin‐4(3 H )‐one 2,2‐dioxide] in controlling jimsonweed to that of hand weeding. Greater densities of jimsonweed resulted in greater losses in soybean yields. Jimsonweed at a low density of 0.3 plants m −1 of row reduced yield by as much as 8%, while jimsonweed at a higher density of 1.6 plants m −1 of row reduced yield by as much as 24%. Increased delay of jimsonweed emergence following soybean emergence markedly reduced soybean yield losses. Jimsonweed at a density of 1.6 plants m −1 of row emerging 2 and 4 weeks after soybean emergence decreased yields by 7 and 3%, respectively, compared to a 23% reduction in yield when jimsonweed emerged with soybean. As duration of competition increased, yields decreased. At a density of 1.6 plants m −1 of row jimsonweed competing with soybean for 2 and 4 weeks reduced yields up to 7 and 14%, respectively. Jimsonweed competing with soybean for the full season reduced yield up to 41%. Soybean stand was not affected by jimsonweed density, time of emergence, or duration of competition. Bentazon was just as effective as hand removal for terminating jimsonweed competition at all application dates.