Which weather factors can affect pesticide performance, including efficacy, volatilization, drift, and residue decay?

• A. Lighting conditions only.
• B. Brand of product.
• C. Temperature, humidity, wind speed/direction, and rain.
• D. Soil type.

Answer: (C)

Weather conditions shape how a pesticide behaves after it’s applied, influencing how well it works, how much it volatilizes, how far it drifts, and how long residues remain on surfaces. Temperature matters because it changes how quickly the chemical evaporates and how fast it degrades. Higher temperatures tend to increase volatilization and can alter reaction rates, which can reduce efficacy on the target and raise the risk of off-target movement. Humidity influences how fast spray droplets dry; more humidity generally slows evaporation, helping droplets stay on the target longer and improve coverage, while also affecting some degradation processes. Wind speed and direction drive drift: strong or gusty winds push droplets away from the target area, reducing efficacy and increasing the risk of off-target contamination. Rain, especially soon after application, can wash pesticides off treated surfaces, dilute residues, and promote runoff or leaching, all of which diminish effectiveness and shorten residue life.

The other options don’t capture these essential weather-related effects. Lighting conditions aren’t the main weather factors that determine drift, volatilization, and residue persistence, and the brand of product or soil type refer to formulation or site characteristics rather than weather.