How to reduce spray drift

Keep spray drift problems at bay by paying attention to weather conditions, spray pressures and nozzle sizes. Reduce spray drift for the health of your plants, people and profits.

Reduce herbicide drift by using low water volumes, spraying at low pressures and using large droplet size nozzles, said Hannah Mathers, extension specialist at Ohio State University.

“Chemical damage to ornamental plants can be extremely expensive, and replacement costs are generally much higher than for other crops,” she said.

Calibrating sprayers and selecting nozzles is as critical a step as choosing the herbicide and applying it, said Scott Bretthauer, extension specialist of application technology at University of Illinois.

A couple of simple tests will help determine the correct nozzle, Bretthauer said.

“Use water-sensitive paper to test your coverage, and place some downwind,” he said. “With air-blast sprayers, do a test with water and dye to make sure the vast majority of spray is getting on the foliage.”

Nozzle choice

Chemical labels dictate droplet size range -- fine, medium or coarse. Using this system allows the user to select many different nozzle and pressure settings, said Steven Thomson, research engineer at USDA-Agricultural Research Service’s Application and Production Technology Research Unit.

Drift reduction nozzles for ground application include Turbo Teejet, Teejet Air Induction, Greenleaf Turbo Drop and VariTarget, he said.

Choose use-extended range or air-induction nozzles for larger droplets, said Loren Bode, professor of agriculture and biological engineering at University of Illinois.

Growers may opt for a drift-control additive to use with existing nozzles. The additive is a long-chain polymer that changes the way drops are formed, Bode said.

Weather conditions

Wind speed and temperature inversions are serious factors affecting spray drift, Thomson said.

“It’s a misconception that you should spray early in the morning when it’s calm,” Thomson said. “A slight breeze is best -- 2 mph is ideal to get turbulent mixing.”

But don’t spray when winds are more than 10 mph.

Keep good records of wind speed and direction, in case you get a drift complaint or need to identify drift damage, Bretthauer said.

Temperature inversions exist during calm conditions. Inversions occur when air temperature increases with altitude instead of decreasing. It acts as a cool blanket of air above the ground, he said. Any spray deposited within an inversion will float until the inversion breaks down, he said.

High humidity also increases drift hazard under inversion conditions.

For more: Hannah Mathers, Ohio State University, (614) 247-6195; mathers.7@osu.edu. Scott Bretthauer, University of Illinois, (217) 333-9418; sbrettha@uiuc.edu. Steven Thomson, ARS, (662) 686-5240; steve.thomson@ars.usda.gov. Loren Bode, University of Illinois, (217) 333-8355; bode@uiuc.edu.

Activate herbicides according to label

Help reduce herbicide drift by activating herbicides within the timeframe indicated on the label, said Hannah Mathers, extension specialist at Ohio State University. The more volatile the chemical, the shorter the period to activate, she said.

Pre-emergent herbicide time of activation

Herbicide injury: Know the signs

Recognizing the symptoms of herbicide injury may help identify the occurrence of herbicide drift. Mike Schnelle, extension specialist at Oklahoma State University, described the typical warning signs.

* Leaf chlorosis is a common symptom of herbicide injury in plants. Often, soil-applied herbicides are responsible for this type of symptom. Chlorosis also is a symptom of poor nutrition. Herbicide-induced chlorosis differs from nutritional chlorosis by a bright-yellow to white interveinal space contrasted with sharply defined secondary bright-green veins.

* Foliar spotting may be a result of herbicide spray drift. Promptly wash any herbicide residue from the foliage of nontarget plants.

* Overall necrosis can occur in advanced stages of herbicide poisoning.

* Epinastic growth, meaning foliage or stems are abnormally twisted, cupped or distorted.

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For more: Mike Schnelle, Oklahoma State University, (405) 744-7361; mike.schnelle@okstate.edu.

- Kelli Rodda