Weed Control Decision Rules under Uncertainty

A model of weed control, which took into account the stochastic nature of crop price, yield, and weed density, was developed to assist farmers in determining weed densities that justify herbicide application and the optimal rate of application. In an application of cocklebur control in soybeans, it was found that the value of following the "if-then-else" treatment strategy versus a fixed application rate regardless of weed density was approximately $25 per acre at low weed numbers. Profits of the marginal treatment strategy are higher than the "if-then-else" strategy, but may not be sufficient to cover the additional informational costs. Under both strategies, the total amount of herbicide applied decreases with increases in uncertainty under the assumption of risk neutrality. The result is due to the convex relationship between weed density and yield loss. Under the assumption of maximizing expected utility, there are instances in which herbicide use increases with risk aversion as per conventional wisdom.