Cultural and Chemical Weed Control Systems in Soybeans (Glycine max)

Combinations of herbicides applied preemergence and postemergence, with and without cultivation, were evaluated for their effectiveness for controlling weeds in soybeans [ Glycine max (L.) Merr. ‘Williams’]. Annual weeds were controlled best when a sequential treatment of a mixture of alachlor [2-chloro-2′,6′-diethyl- N -(methoxymethyl)acetanilide] + linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] was applied preemergence, and glyphosate [ N -(phosphonomethyl)glycine] was applied postemergence, followed by one cultivation. The largest soybean yields were obtained when alachlor + linuron applied preemergence was followed by a cultivation, bentazon [3-isopropyl-1 H -2,1,3-benzothiadiazin-4(3 H )-one 2,2-dioxide] applied postemergence, bentazon applied postemergence and a cultivation, or glyphosate applied postemergence and a cultivation. Regression analysis of the soybean yield vs. weed control data for all treatments indicated that soybean yields were suppressed an average of 180 kg/ha when glyphosate was applied postemergence. A cultivation in addition to the preemergence and postemergence treatments improved both weed control and soybean yield.