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Wheat School: Understanding spray drift to reduce the risk

By: RealAgriculture Agronomy Team

July 15, 2021

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Spray drift happens, but every spray operators goal should be to create as little drift as possible. So how can we combat it?

Tom Wolf, founder of AgriMetrix and co-founder of Sprayers 101, joins Kara Oosterhuis for this Wheat School episode for a technical breakdown of spray drift, and tips for how to prevent it.

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Not only are non-target crops a concern with drift, but also the image of agriculture on the whole. Drift is a loss of product on the ground, and can also become a pollutant, Wolf says.

“Drift remains perhaps the biggest ambassador of agriculture in the modern era,” says Wolf. “People see sprayers and they worry about drift.”

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Drift is still a bit of a conundrum, says Wolf, because there are counter-acting forces. For example, wind’s really important because the windier it is, the more small droplets will leave the spray cloud produced by the sprayer. “On the other hand, what happens to it once it leaves; wind can be your friend, because wind actively creates turbulence in the atmosphere and it dilutes the spray cloud that you’ve lost.”

Different products atomize differently, so certain formulations can cause finer droplets, says Wolf. Other factors include what the active ingredient is, and what crops are downwind of the target crop. (Story continues below)

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Another complicated factor is inversions and, as Wolf explains, the common practice for when it’s too windy to spray, is to spray when it’s dead calm, early morning or late at night. But, when an inversion occurs, the spray plume stays put, then slowly moves, following slopes or travelling on small winds, in a concentrated form.

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“It’s generally been dry, and people are concerned about the lifetime of droplets,” says Wolf. “We’ve been advised not to spray when it’s too hot for example. Really, the best measure of droplet life expectancy in terms of evaporation, is Delta T (an atmospheric moisture measurement).”

Pesticides are typically not taken up that well when they’ve dried on a leaf, they work better when the leaf is wet, so preserving that droplet on the leaf is important. The droplet can also evaporate a significant amount, and shrink in diameter, even while traveling between the boom and the ground, which can create another drift situation.

The easiest solution to the problem, is to consider nozzles that will put out larger droplet sizes, says Wolf, perhaps specific to the product applied.