Spray drift
- Also known as
- drift, drift reduction agent, DRA
Spray drift is the movement of spray droplets or vapor away from the intended target during or after an agricultural application. It wastes product, reduces control on the target, and can harm nearby crops, people and the environment.
What is spray drift?
When a crop protection or nutrient product is sprayed, some of it can end up somewhere other than the target. Spray drift covers two forms:
- Particle drift: small droplets carried off target by wind during application.
- Vapor drift: product that evaporates after application and moves as a gas, a concern with some volatile herbicides.
What causes particle drift
- Droplet size. Fine droplets, commonly those smaller than about 150 micrometers, stay airborne longer and drift farther. Nozzle type and spray pressure largely determine droplet size.
- Wind speed and direction.
- Boom height and application method. Higher booms and aerial application give droplets more distance to travel.
- Temperature inversions, when cool air near the ground is trapped under warmer air, which can hold fine droplets aloft and carry them long distances.
- Heat and low humidity, which make droplets evaporate and shrink.
How drift is reduced
- Drift-reducing nozzles, such as air-induction nozzles, that produce coarser droplets.
- Lower spray pressure and boom height.
- Spraying in suitable weather, avoiding high winds and inversions.
- Buffer zones near sensitive areas.
- Drift reduction agents, adjuvants that increase droplet size and reduce the share of fine droplets.
Coarser droplets can reduce coverage, so applicators balance drift control against the coverage the product needs. The EPA runs a program that evaluates drift reduction technologies, and many product labels specify droplet size and weather conditions.
Frequently asked questions
Particle drift is the movement of spray droplets during application. Vapor drift is movement of product that has evaporated after it was applied.
Some do. Drift reduction agents increase droplet size. Other adjuvants, such as some surfactants, can make droplets smaller, so adjuvant choice should consider drift.
Sources
- Introduction to pesticide drift; drift reduction technology program, U.S. Environmental Protection Agency
- Reducing spray drift, Land-grant university extension