Pesticide drift is the airborne movement of pesticides from an area of application to any unintended site. Drift can happen during pesticide application, when droplets or dust travel away from the target site. It can also happen after the application, when some chemicals become vapors that can move off-site. Pesticide drift can cause accidental exposure to people, animals, plants and property.

Particle and Vapor Drift

You might think of pesticide drift as the movement of spray droplets during application. This is called 'particle drift.' But, some pesticides are more likely to drift in the form of vapor. This can happen after an application even when the pesticide was applied as a solid or liquid. This is called 'vapor drift,' and an important factor is the pesticide's vapor pressure.

Pesticide drift can pose health risks to people and pets when sprays and dusts drift to nearby areas such as homes, schools, and playgrounds. Wildlife and plants are also at risk when drift affects natural areas and water sources. Herbicide drift can damage other nearby crops or make them unsellable if the active ingredient is not registered for a particular crop. Pesticide drift also results in wasted pesticide product. EPA estimates up to 70 million pounds of pesticides are lost to drift each year.

If you suspect a case of pesticide drift, contact your state pesticide regulatory agency. Often, it's illegal to apply pesticides in a manner that allows them to move off-site.

Reading the Pesticide Label

Reading the label is the first and most important way to minimize risk and exposure. Understanding the approved use instructions will help reduce the risk of drift. There are four main drift factors the EPA focuses on when reviewing pesticide product registrations:

• Minimum and maximum wind speed
• Spray droplet size
• Spray release height
• Buffer zones, if applicable

Ways to minimize or prevent pesticide drift:

• Adjust your nozzle(s) and pressure to make bigger droplets. Bigger droplets fall faster, so they are less likely to drift with the wind.
• Apply pesticides during calm weather conditions. High winds can increase the risk of drift.
• Avoid applications when there is fog hanging in the air. It may indicate that a 'temperature inversion' may be taking place. That increases the risk of pesticide drift.
• Applying some herbicides before hot weather can lead to vapor drift. That vapor can seriously damage nearby plants.
• Read the herbicide labels carefully to learn more.
• Direct sprays away from property lines. Keep the wand or hose as close as possible to the target.
• If you have to treat a tree near your property line, consider talking to your neighbor first. They may take steps to avoid any potential exposure.
• Use your best judgment, with your unique knowledge of the site and the application equipment to keep the product on target.
• Read and follow the label directions carefully. The label may prohibit applications under certain weather conditions, using high-pressure sprays, or using certain nozzles.

Additional Resources:

• Pesticide Drift - Pesticide Environmental Stewardship Program
• Reducing Pesticide Drift - Environmental Protection Agency (EPA)
• Ways to Reduce Spray Drift and Other Considerations - PennState Extension
• Pesticide Volatilization - Environmental Protection Agency (EPA)
• Understanding Pesticide Drift and Drift Reduction Strategies - Montana State University Extension
• Pesticide Drift - California Department of Pesticide Regulation (CDPR)
• Pesticide Drift Management - Oregon State University, Integrated Plant Protection Center
• Pesticide Spray Drift (video) - Ontario Ministry of Agriculture, Food and Rural Affairs
• Air Temperature Inversions - North Dakota State University Extension

If you have questions about this, or any pesticide-related topic, please call NPIC at 800-858-7378 (8:00am - 12:00pm PST), or email at npic@ace.orst.edu.