Which factor most directly affects the potential for spray drift?

• A. Temperature
• B. Wind speed
• C. Droplet size
• D. Humidity

Answer: (C)

Droplet size is the key factor that controls how far spray droplets can travel. The physics of how droplets fall through air show that smaller droplets have a much slower rate of vertical descent, so they stay suspended longer and are more easily carried by even modest air currents. That makes drift—the movement of spray away from the target—more likely with tiny droplets.

Larger droplets fall out of the air quickly and are less influenced by wind, so they deposit closer to the target and drift less. Temperature, wind speed, and humidity do affect drift, mainly by changing air movement and evaporation, but they influence drift indirectly. The amount of drift you get is most directly determined by how small the droplets are when they leave the nozzle.