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Herbicide drift not always wind-based

Spray drift can also happen when it’s calm, and the consequences can be dire

“It’s tempting to spray while it’s calm, but if there’s no wind the droplets will often stay suspended for a while behind the sprayer,” says Dr. Tom Wolf.

As many farmers have found out the hard way, herbicide doesn’t always go where you direct it.

“Any time an application of spray is made, there are always small droplets that can move away from the intended target,” said Dr. Tom Wolf, applications specialist with Agrimetrix Research & Training.

Generally speaking, herbicide drift is linked to wind, yet that only tells part of the story.

“When we apply spray, droplets emerge from the nozzle that range in size from two mm down to five microns, which is basically invisible to the human eye. Because the particles are so tiny, they aren’t really affected by gravity and tend to float like a mist or smoke or fume, moving with the air currents.”

Since drift is linked to wind, the solution is simply to spray when it’s not windy, right? You knew it couldn’t be that easy.

“It’s tempting to spray when it’s calm, but if there’s no wind the droplets will often stay suspended for a while behind the sprayer.”

When the first breeze occurs the next morning, those droplets will move with it, often to somewhere they shouldn’t be.

One person who has seen the consequences of herbicide drift is Jason Deveau, application technology specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs. Known in the industry as the “spray guy,” Deveau — along with Wolf — has written extensively on the topic for and on Twitter (@nozzle_guy for Wolf and @Spray_Guy for Deveau).

“If a herbicide goes astray it can damage someone else’s crop and have a huge financial impact,” said Deveau. “It can also stir up a lot of hard feelings as people get emotional when their livelihood is affected.”

So emotional, in fact, that a northeast Arkansas cotton, soybean and corn farmer was shot to death earlier this year, allegedly in an argument over dicamba herbicide drift. For that reason, Deveau said communication is critical in combating the problem.

He also advises following herbicide label instructions closely, especially in regard to buffer zones.

“Under Health Canada regulations you may not release one of these products within a certain distance downwind of sensitive areas like bodies of water or population centers.”

Lowering the boom

Other tactics for lowering drift risk include limiting the height of the boom so wind is less apt to pull the spray away from the target, and limiting driving speed as higher speeds tend to increase drift.

And while just avoiding wind isn’t the answer in itself, Deveau said you can safely assume that “if you’re chasing your hat around the field, it’s probably not the best time to spray.”

For Wolf, the lack of a clear-cut solution to herbicide drift is a real source of frustration.

“I have been working in this area of research my whole career and I never expected herbicide drift to stay at the forefront of our concerns for as long as it has. The problem remains largely unsolved and causes great difficulty for our industry, so it’s something we really have to get a handle on.”

Two things offering him some hope are the move to low drift nozzles and the use of automatic boom height holders. Still, he’s concerned that with the push to improve productivity, farmers are driving their sprayers faster and raising boom heights, thereby exacerbating the problem.

And his concern doesn’t end there.

“We are about to embark on a new generation of genetically modified crops and will be spraying dicamba on them. It has the potential to do a lot of harm to other crops if it drifts so we have to be extremely cautious.”

The issue of herbicide drift is here to stay.

About the author


Geoff Geoff Geddes is a freelance agriculture and business writer based in Edmonton. Find him online at or email [email protected]

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