Soybean Growth as Influenced by Planting Date, Cultivation, and Weed Removal1

Abstract Knowledge of weed interference is important for designing weed control systems for agronomic crops. Research was initiated to determine the critical periods of weed interference in soybean [Glycine max(L.) Merr.] and the minimum weed removal requirements needed to achieve optimum seed yields. In a field infested with mainly broadleaf weeds, a 4‐week weed‐free period after planting was needed to achieve optimum yields in early and late planted soybean grown on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Plots cultivated about 3 and 5 weeks after planting required only one handhoeing 2 weeks after planting to obtain optimum soybean yields. Weeds left 4 weeks before removal, but not 6 weeks, did not reduce soybean yields in early or late planted soybean. Results indicate that if soybeans are kept weed‐free the first 4 weeks after planting or if weeds are not left undisturbed longer than 4 weeks after planting, optimum soybean yields should occur.