FIELD-EVALUATION OF A BIOECONOMIC MODEL FOR WEED MANAGEMENT IN SOYBEAN (GLYCINE-MAX)

A bioeconomic model was tested as a decision aid for weed control in s oybean at Rosemount, MN, from 1991 to 1994. The model makes recommenda tions for preplant incorporated and preemergence control tactics based on the weed seed content of the soil and postemergence decisions base d on weed seedling densities. Weed control, soybean yield, herbicide u se, and economic return with model-generated treatments were compared to standard herbicide and mechanical control systems. Effects of these treatments on weed populations and corn yield the following year were also determined. In most cases, the model-generated treatments contro lled weeds as well as a standard herbicide treatment. Averaged over th e 3 yr, the quantity of herbicide active ingredient applied was decrea sed by 47% with the seedbank model and 93% with the seedling model com pared with a standard soil-applied herbicide treatment. However, the f requency of herbicide application was not reduced. Soybean yields refl ected differences in weed control and crop injury. Net economic return to weed control was increased 50% of the time using model-recommended treatments compared with a standard herbicide treatment. Weed control treatments the previous year affected weed density in the following c orn crop but had little effect on weed control or corn yield. The bioe conomic model was responsive to differing weed populations, maintained weed control and soybean yield and often increased economic returns u nder the weed species and densities in this research.