PROSPECTS FOR WEED-CONTROL THROUGH CROP INTERFERENCE

Crop interference with weed growth is a fundamental method of nonchemical weed control. Crop interference, entailing weed suppression, should be distinguished from crop tolerance of weeds, i.e., relatively small yield loss due to the presence of weeds. Tolerance is less desirable than interference in that it may lead to increases in weed seed populations that can cause future yield losses. Ideally, interference should occur as early as possible in growth to prevent resource consumption by weeds. A path analysis of crop-weed interference is presented. The model can be used to estimate the relative magnitude of early vs. later crop interference with weed growth, and to identify crop traits that contribute to interference with weed growth. Such analysis can identify crop varieties that show strong.early interference with weed growth, and traits associated with strong early interference. For illustrative purposes, the model is applied to characterize differences among soybean varieties in interference with common cocklebur. Weed control by crop interference could be enhanced by crop breeding and management. However, several benefits and costs of interference should be evaluated before undertaking such approaches. First, the degree to which crop interference can substitute for other forms of weed control must be determined. Second, yield costs associated with interference should be measured; these may occur in crop varieties that interfere strongly with weeds, particularly when water, temperature, and mineral nutrients are limiting. A more mechanistic understanding of crop interference is needed so that interference can be enhanced through crop breeding and management while minimizing yield costs.