Avoid Spray Drift

By John Wilson, Extension Educator

One night last week I got one of my least favorite calls that it seems I get about this time each summer. A homeowner was rightfully concerned because their garden had been sprayed when a neighboring field was being treated. We’re still trying to figure out what was being sprayed, but unfortunately if the product is not labeled for use on a garden, then it would not be safe to eat the produce from their garden that they had worked on all spring and summer.

Virtually every pesticide application produces some drift. How much drift depends on factors such as the nozzles used, the formulation of the material applied, how the material is applied, the volume used, and the prevailing weather conditions at the time of application. All drift is illegal and can cause potential injury to non-target plants and animals, and has the potential for producing illegal residues on non-target sites.

While it is impossible to eliminate all drift, there are things that can be done to minimize the risk of the uncontrolled airborne movement of spray droplets, vapors, or dust particles, away from the intended point of application.

Drift control is the applicator’s responsibility! Drift cannot be completely eliminated, but it can be greatly reduced. Here are some practices that can reduce potential drift problems:

• Use as coarse of a spray as possible and still obtain good coverage and control. For sprays, use formulations which give large diameter, 150 – 200 microns or larger, spray droplets. Droplet size is one of the most important factors affecting drift… but addressing droplet size alone is not sufficient to reduce the probability of drift and potential damage.
• Don’t apply pesticides under windy or gusty conditions; don’t apply at wind speeds over 15 mph, ideally not over 5 mph. Read the label for specific instructions.
• Maintain adequate buffer zones to insure that drift does not occur in off-target area. Allow extra buffer when spraying near sensitive crops, neighboring farmsteads, or streams and ponds.
• Be careful with all pesticides. Insecticides and fungicides usually require smaller droplet sizes for good coverage and control than herbicides. But herbicides have a greater potential for off-site damage.
• Choose an application method that is less likely to cause drift. Aerial applications maybe the only option for some situations, but are more prone to drift problems so extra precautions are required.
• Use drift control or drift reduction agents. These materials are basically thickeners and are designed to minimize the formation of droplets smaller than 150 microns.
• Choose the pesticide formulation carefully if you have a choice in products to use. Water-based products will volatilize more quickly than oil-based products. However, oil-based sprays can drift farther because they are lighter, especially above 95°F.
• Apply pesticides early in the morning or late evening; the air is often more still than during the day. Also, don’t spray during thermal inversions, when air closest to the ground is warmer than the air above it. When possible, avoid spraying at temperatures above 90°-95°F, ideally not over 85°F.
• Know your surroundings! Determine the location of sensitive areas near the application site such as homes, surface waters, organic production, fruit or vegetable production, grapes, and  honey bees.  You should know the location of sensitive areas within a half mile radius of sites on which you would make, or have someone else make, pesticide applications, and one mile downwind. Make pesticide application decisions with these locations and wind direction in mind.
• Use a drift-reducing spray nozzle that produces larger droplets.
• And finally, determine wind speed and direction and take this into account in determining application timing, equipment, and whether or not to make an application. Too strong of a wind or the wrong wind direction can cancel out everything else you have done to reduce drift.

For more information on reducing spray drift, contact your local Nebraska Extension office.