Initial Pesticide Certification Practice Test 2026 - Free Pesticide Certification Practice Questions and Study Guide

High humidity slows the evaporation of pesticides from treated surfaces or spray droplets. When the air is already saturated with water vapor, the driving force for a pesticide molecule to leave the droplet and enter the air is reduced, so volatilization is lower. In humid conditions, droplets can also absorb moisture and grow, which lowers the surface-area-to-volume ratio and further reduces evaporation. Therefore, high humidity tends to decrease volatility. This is why volatility isn’t increased or unaffected by humidity, and it isn’t primarily driven by wind speed—the humidity-specific effect is a dampening of volatilization.