Competition of Johnsongrass and Cocklebur with Six Soybean Varieties

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Abstract
Heavy infestations of johnsongrass(Sorghum halepense(L.) Pers.) reduced the yield of six soybean(Glycine max(L.) Merr.) varieties 23 to 42% with both hand-harvesting and mechanical-harvesting over a 3-year period. ‘Davis', ‘Lee’, and ‘Bragg’ varieties produced significantly higher yields than did ‘Semmes', ‘Jackson’, or ‘Hardee’ when grown in weed-free plots, but ‘Bragg’ produced significantly higher yields than all other varieties when grown with johnsongrass. Less regrowth of johnsongrass occurred in plots of ‘Bragg’, ‘Davis', and ‘Semmes' than in plots of ‘Lee’, ‘Jackson’, and ‘Hardee’. Common cocklebur(Xanthium pensylvanicumWallr.) reduced the average yields of six soybean varieties 63 to 75% when plots were hand-harvested. ‘Semmes' showed the lowest percentage yield reduction from common cocklebur competition when hand-harvested, and ‘Semmes' and ‘Bragg’ showed 53% to 57% reduction respectively when machine harvested.