Illinois Field Crop Applicators Practice Test

During the vegetative growth stage, what percentage of defoliation represents the economic threshold for bean leaf beetles?

1. 10% defoliation or 2-5% injured pods

2. 20% defoliation or 5-10% injured pods

3. 30% defoliation or 15% injured pods

4. 40% defoliation or 10-15% injured pods

The correct answer is: 20% defoliation or 5-10% injured pods

The economic threshold for bean leaf beetles during the vegetative growth stage is determined by the level of defoliation that begins to result in economic damage. In this context, 20% defoliation reflects a point where the cost of managing the pest may be beneficial compared to the potential yield loss caused by the beetle's feeding habits. Bean leaf beetles can also injure the pods later in development, and the threshold for pod damage becomes critical as well, making the range of 5-10% injured pods significant. This percentage of injured pods indicates that while some damage is acceptable, surpassing this threshold warrants action, as it could lead to decreased yields. The chosen answer emphasizes the balance between crop health and economic viability, underscoring the importance of monitoring pest populations and their impact on overall crop productivity. This understanding helps guide field applicators in making informed decisions regarding pest control measures in relation to yield losses and cost-effectiveness.