Wind can be an applicator’s friend, says expert

A windy day can provide ‘directional certainty,’ but farmers should avoid spraying in extreme conditions

Wind, wind, wind: it keeps the bugs away, but if you’re a busy farmer with thousands of acres of crop to spray, it can be a royal pain in the neck.

Applying expensive and potentially damaging chemicals in windy conditions is not an ideal scenario, says Tom Wolf, a chemical application expert and president of Agrimetrix.

But for farmers facing tight schedules, it’s often unavoidable.

The secret to success is planning ahead, assessing your risks and managing spray drift by controlling the variables that you can control — most notably boom height, ground speed, field selection, nozzle selection and chemical selection.

And remember, wind is not always the enemy.

“If it’s windy, you have directional certainty,” said Wolf.

“In other words, you know what’s downwind. You know if you have a sensitivity issue. And at least you can make an assessment.

“Secondly, you do have some tools at your disposal to minimize drift, even when it’s windy. You can use coarser sprays … you can drive slower, which reduces exposure to drift, you can lower your booms, and you can leave buffers….

“Don’t spray close to sensitive areas. Instead, spray 90 percent of the field, but stop short of the sensitive areas and (finish) the field another day when the wind conditions are better.”

Wolf said growers should avoid spraying in extreme wind.

“We very rarely observe significant losses of product performance on the field that’s being sprayed, even at very high wind speeds,” he said.

“But that doesn’t give you license to spray under extreme winds. The downwind risks should always be considered. Philosophically speaking, it’s our responsibility, as an industry, to apply our products under safe conditions.”

So what is the threshold for safe application?

That’s a tough question to answer, Wolf said.

Some growers may be comfortable spraying in 35 km-h wind with gusts up to 50 km. Despite significant potential for drift losses, they are still satisfied with chemical efficacy, based on past experience.

If chemicals are being applied under border line conditions, remember the basics: identify risk-sensitive areas, choose target fields carefully and control the variables that you can control.

In addition, always consider the properties of the chemical you’re applying.

In other words, ask yourself, how suitable is the product you’re spraying for use with low drift nozzles?

“Low drift nozzles, really, are the primary technology that we rely on to allow us to spray under windy conditions, but when you’re talking about making the spray coarser, some active ingredients are much less effective than others,” Wolf said.

“For example, glyphosate is very tolerant of being used with bigger droplets, so even though glyphosate can be quite harmful to crops downwind, it lends itself to spraying in windier conditions.

“On the other hand, if you’re going to go with something like Liberty, it’s not well suited to coarse droplets so you should probably pick a better day to spray Liberty than glyphosate.”

Wolf said one of the most common dilemmas faced by busy producers and applicators is deciding whether to spray during the day under windy conditions or at night, when conditions are often dead calm.

“A lot of producers will tend to push their spraying activity into the evening and night hours to take advantage of those calm conditions,” he said.

“But experts like myself have for years been advising our clients to not spray in calm night conditions because of inversions.”

Inversions occur only when chemicals are applied at night under calm conditions.

In essence, the spray cloud lingers in the air and doesn’t disperse properly. It remains suspended, moves slowly and retains its potency, increasing the risk of damage to adjacent fields.

By comparison, applying chemicals during sunny or windy conditions ensures some level of mechanical and/or thermal turbulence, which disperses the spray cloud and reduces the risk of unintended damage.

“What that means is that even though you’re losing more drift, it’s being rapidly diluted in the atmosphere and therefore is less likely to cause damage downwind. It disperses,” he said.

“My dilemma, as a professional adviser, is that I don’t really want to advise people to spray when it’s windy … but I will say this: if you have a choice between spraying at night when it’s perfectly calm or spraying during the day when it’s sunny or windy, I would choose the latter.

“Conditions may not be perfect, but you do have more tools at your disposal to control the outcome.”

For more information on minimizing drift losses, avoiding unintended chemical damage and optimizing chemical efficacy, readers can visit Wolf’s website at A blog article that deals with drift issues can be viewed at

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