Pesticide drift occurs as vapor drift and droplet or spray drift.
Particle or Droplet Drift
Most pesticide drift occurs immediately after the application. Small droplets are more likely to drift than larger droplets. A number of factors influence droplet size, including formulation, nozzle type, sprayer pressure, and weather conditions. Ultimately, it is the applicator's responsibility to consider all the factors that will impact drift of the specific application, before deciding whether to spray or not to spray
Vapor drift
The active ingredient of some pesticides can evaporate or volatilize during application, or for several hours afterward. When vapor containing the pesticide active ingredient moves off the application site, it may cause plant damage, contamination or human health risks. Volatility is based on the vapor pressure of the pesticide, and, in general, higher air temperatures increase the probability of vapor drift. Read the pesticide label for specific procedures and warnings, such as maximum temperatures or soil incorporation requirements, to reduce the potential for vapor drift. An example of a label warning statement would be: "avoid application when temperatures may exceed 85° F during or 24 hours following the application."
Drift can cause aesthetic as well as economic injury. The oak, on the left will grow past the damage. A tobacco buyer would not accept 8 acres of tobacco affected by drift, on the right.
Authored by Jim Wilson, PhD
South Dakota State University
