Determining when to apply a pesticide includes consideration of:

The correct choice emphasizes the importance of understanding both the life cycle of the pest and the prevailing weather conditions before applying a pesticide. Knowledge of the pest's life cycle is crucial because different stages may be more susceptible to control measures than others. For example, some pests may be more vulnerable during their larval stage than as adults. Weather conditions also play a significant role, as they can affect pest activity, pesticide efficacy, and potential drift. For instance, applying a pesticide before a rainstorm can lead to runoff, diminishing its effectiveness and potentially causing environmental harm. By considering both factors, applicators can optimize their pest management strategies, ensuring that interventions are timely and effective.

The other choices, while relevant to overall pesticide application practices, are not as directly related to the timing of pesticide applications. Additives might enhance pesticide performance, the percentage of active ingredient informs dosage, and safety measures are critical for the applicator and environmental protection but do not specifically address the timing of when the application should occur.