INTEGRATED WEED MANAGEMENT-TECHNIQUES TO REDUCE HERBICIDE INPUTS IN SOYBEAN

Information on integrated weed management systems is needed so that producers can develop systems that minimize the environmental impacts of weed control without sacrificing profitability of crop production. Reduced rates of broadcast- or band-applied alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] plus metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and rotary hoeing, each in combination with between-row cultivation, were evaluated for weed control in soybean [Glycine mar (L.) Merr.l. One or two between-row cultivations allowed for a 50 to 75% reduction in the amount of herbicide used without reducing weed control or soybean yield. Reducing herbicide rates also decreased soybean injury. Two passes of a rotary hoe reduced weed densities up to 75% and increased the effectiveness of subsequent cultivations. However, two passes of the rotary hoe reduced soybean density as compared to other treatments. In 1989, under low weed densities, several mechanical weed control systems resulted in soybean yields similar to the weed-free control. In 1990, under greater weed densities, mechanical weed control systems resulted in reduced soybean yields compared to weed control systems that included herbicides. Based on the results of this research, switching from chemical-intensive systems to mechanical weed management systems under high weed pressure is not advisable. Under high weed pressure, reduced rates of herbicide, broadcasted or banded over the soybean row, in combination with cultivation provided excellent weed control. Mechanical weed control as a part of an integrated weed management system should maximize weed control while minimizing herbicide use.