How does weather affect pesticide efficacy and safety?

• A. The weather has no effect on pesticide performance.
• B. Temperature, humidity, wind speed, and rain affect evaporation, volatilization, uptake, and drift; apply under conditions specified by the label.
• C. Only wind speed matters.
• D. Only humidity matters.

Answer: (B)

Weather conditions shape how a pesticide behaves after you apply it and how safely you can do the work. Temperature changes how fast a product evaporates or volatilizes, how quickly it degrades, and how readily pests or plants take it up. Humidity affects how long spray droplets stay on leaf surfaces and can influence foliar absorption and potential phytotoxicity. Wind speed drives drift—the movement of droplets off-target—which is a major factor in safety for bystanders, non-target crops, and wildlife. Rain or predicted rainfall after application can wash the product off the target, reduce efficacy, and cause environmental runoff, while a dry period helps the spray deposit and dry properly. Because these factors alter both effectiveness and safety, the label specifies the weather conditions in which the product should be applied. Following those conditions—considering temperature, humidity, wind, and rain—helps ensure the pesticide works as intended and minimizes risks.