MODELING THE POPULATION-DYNAMICS AND ECONOMICS OF VELVETLEAF (ABUTILON-THEOPHRASTI) CONTROL IN A CORN (ZEA MAYS)-SOYBEAN (GLYCINE-MAX) ROTATION

A simulation model was developed to predict the population dynamics an d economics of velvetleaf control in a corn-soybean rotation. Data com piled from the literature were used to parameterize the model for two situations, one in which velvetleaf was infected by a Verticillium spp . wilt and one without infection. Verticillium was assumed to have no effect on corn or soybean yield. In the absence of control, simulated seedbank densities of a Verticillium-infected velvetleaf population we re 5 to 50 times lower than for an uninfected velvetleaf population. T he model was used to evaluate a threshold weed management strategy und er the assumption that delvetleaf was the only weed and bentazon the o nly herbicide available for its control. In the absence of Verticilliu m, an economic optimum threshold of 2.5 seedlings 100 m(-2) afforded t he highest economic returns after 20 yr of simulation. Simulations in which velvetleaf was infected in 8 out of 20 randomly assigned years i ndicated a 6% increase in annualized net return and an 11% reduction i n the number of years that control was necessary. Sensitivity analysis indicated the parameter estimates having the greatest impact on econo mic optimum threshold were seedling emergence and survival, maximum se ed production, and herbicide efficacy. Under an economic optimum thres hold of 2.5 seedlings 100 m(-2), management practices that manipulate the most sensitive demographic processes increased annualized net retu rn by up to 13% and reduced long-term herbicide use by up to 26%. Resu lts demonstrate that combining an economic optimum threshold with alte rnative weed management strategies may increase economic return and re duce herbicide use.