How do weather conditions influence herbicide performance and drift risk?

• A. Only rainfall affects drift risk.
• B. Temperature is not relevant to drift.
• C. Wind, temperature, and humidity affect drift, volatilization, and uptake; apply only under label-specified weather conditions.
• D. Sunlight alone determines evaporation rate.

Answer: (C)

Weather conditions shape how a herbicide moves and works after you spray it. Wind carries droplets away from the target, so higher wind speeds increase drift risk and reduce precision. Temperature influences how readily the chemical volatizes; warmer temperatures raise vapor pressure for many herbicides, making off-target movement more likely and potentially reducing ground deposition. Humidity affects how droplets evaporate and how plants take up the product; in certain conditions, humidity can slow evaporation and alter leaf uptake, changing efficacy and crop safety. Because these factors interact, labels specify acceptable weather windows to minimize drift and optimize performance. That combination—wind, temperature, and humidity—and following the label’s weather guidance is why this option is the best choice.