Purdue Extension Service

Vanderburgh County, Indiana

Spray Drift Can Be Harmful to Non-Target Organisms

By Larry Caplan, Extension Horticulture Educator, Vanderburgh County, IN

For the Evansville Courier and Press, June 28, 2009

One of the hazards of using pesticides is the risk of the material missing your target and hitting something else. It is for this reason that Purdue and other universities always caution farmers, gardeners, and other chemical applicators to avoid spraying on windy days or before a heavy rain, and to be aware of what is near the spray application area.

Herbicides (weed killers) that miss the weed and hit a desirable plant can damage it, or even kill it. Even a few droplets of glyphosate (Roundup) can kill sensitive flowering plants if it hits their leaves. Some lawn herbicides, especially those that contain Dicamba, can move through the soil and be absorbed by the roots of trees and shrubs.

Insecticides that go off-target can wipe out honeybee colonies or kill butterflies. Most gardeners know not to spray insecticides on blooming plants, so as to protect honeybees and other pollinators. But if you are spraying a tree or shrub for Japanese beetles and the chemical drifts over to your flower garden, you may kill any bee or butterfly that is visiting.

Another problem with drift is that an insecticide, which may be labeled and safe to use on ornamentals, may not be labeled or safe to spray onto an edible crop. Some of the systemic products, like acephate (Orthene) are fine to use to control bagworms on your evergreens; but if the chemical drifts over to your tomatoes, you won't be able to harvest or eat them.

Pesticides don't only move in the air. Some products can be washed away by heavy rain or irrigation. Grub control granules and fertilizers can be washed off the lawn and into nearby sewers or ponds. Long-acting weed preventers can be washed out of driveways into nearby flower beds. If the product has been carefully watered in after application, or if the spray has had a chance to dry, then there is less of a chance of the product washing off your target and into somewhere undesirable.

Overspraying insecticides can have other problems, even if the chemical doesn't drift anywhere. Japanese beetles, because they don't emerge from the ground all at the same time, lead some people to spray more often than the label advises. Not only are you killing Japanese beetles, but you also wind up killing beneficial insects, like ladybugs and predator mites. Ever since these beetles arrived in our area in the mid-1990s, I've seen midsummer population explosions of spider mites on a wide variety of plants, especially burning bush. Many of the "good guys" that would normally feed on the mites are gone, thanks to repeated spraying.

The bottom line when using any type of pesticide is to read and follow all label directions. Take special care to read about the environmental conditions that should be avoided when using the product, especially wind, heat, and rain. And always be aware of where your spray will go if it doesn't hit what you're aiming at.

For more information on safe pesticide usage or reducing your need to spray, contact the Purdue Extension Service at (812) 435-5287.