Under what conditions is pesticide drift less likely to occur?

Pesticide drift is less likely to occur under conditions where the physical movement of pesticide particles through the air is minimized. The correct choice, which includes rain at a sufficient rate, suggests that heavy rain can help to ensure that pesticide residues are either washed away or not allowed to remain airborne, thus significantly reducing drift potential.

When rain falls at around 1 inch every 20 minutes, it creates a situation where any applied pesticides are quickly washed off surfaces or plants, and the heavy rainfall can also suppress airflow that would typically contribute to drift. High rainfall can lead to runoff, which, while it presents other environmental concerns, directly mitigates the risk of airborne movement of pesticides.

In contrast, calm weather conditions can still allow for pesticide application with relatively low drift risk, but there's always some potential for drift, especially from evaporative losses. High humidity generally aids in keeping pesticide droplets heavier and less likely to drift, but it does not eliminate the likelihood entirely. Windy days dramatically increase the potential for drift, as strong gusts can carry pesticide particles over larger distances, making it critical to avoid applications during such conditions.