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 and economics of velvetleaf control in a corn-soybean rotation. Data compiled 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 were 5 to 50 times lower than for an uninfected velvetleaf population. The model was used to evaluate a threshold weed management strategy under the assumption that delvetleaf was the only weed and bentazon the only herbicide available for its control. In the absence of Verticillium, an economic optimum threshold of 2.5 seedlings 100 m(-2) afforded the highest economic returns after 20 yr of simulation. Simulations in which velvetleaf was infected in 8 out of 20 randomly assigned years indicated a 6% increase in annualized net return and an 11% reduction in the number of years that control was necessary. Sensitivity analysis indicated the parameter estimates having the greatest impact on economic optimum threshold were seedling emergence and survival, maximum seed production, and herbicide efficacy. Under an economic optimum threshold of 2.5 seedlings 100 m(-2), management practices that manipulate the most sensitive demographic processes increased annualized net return by up to 13% and reduced long-term herbicide use by up to 26%. Results demonstrate that combining an economic optimum threshold with alternative weed management strategies may increase economic return and reduce herbicide use.