TEXAS A&M AGRILIFE ROLLING PLAINS AGRONOMY PROGRAM

Josh A. McGinty, Paul A. Baumann and Gaylon D. Morgan

Spray drift is the lateral movement of pesticide spray droplets away from the target area before reaching the plant or soil. This differs from vapor drift, which is the off-target movement of a pesticide as a vapor after reaching the plant or soil. Vapor drift is directly related to the formulation of the pesticide product and will not be discussed herein. Reducing spray drift of pesticides should be of utmost importance to applicators as they are legally liable for any damages to off-target plants. Additionally, any pesticide moving off-site is effectively reducing the pesticide rate applied to the intended area. Spray drift is influenced by several environmental factors, including wind speed, air temperature, and relative humidity. These factors must be considered on a day-to-day or even an hour-to-hour basis, but there are additional important decisions in spray equipment setup that must be made well before reaching the field. Nozzle selection, operating pressure, and boom height are all controllable factors impacting the potential for spray drift to occur. Of these three, proper nozzle selection plays the largest role in reducing spray drift. Nozzle design and size directly influence the size of spray droplets. All spray droplets exit the nozzle at the same velocity, but smaller droplets lose velocity more rapidly and thus take longer to fall to the target. The longer a droplet takes to reach the target, the more susceptible it will be to drifting laterally.

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