What is Pesticide Drift?

Growers in Ontario follow integrated pest management programs to protect their crops from insects and disease. Spraying pesticide is often part of that program and the goal is to be safe, efficient and effective.
Of course that's easier said than done; typically there's a very small window of time available to apply pesticides, and the weather doesn't always cooperate.
Spraying under the wrong conditions, such as on hot or windy days, can cause off-target spray drift. Drift is possible every time the sprayer is turned on.
Growers can reduce the impact by understanding the causes of pesticide drift, and making adjustments. To understand how spray drifts, we have to look at droplet behaviour. The forces acting on spray droplets include: Gravity, Evaporation, Wind, Drag and Lift.
Gravity pulls the droplet down out of the air. Evaporation makes droplets smaller. Wind will move droplets. Drag will slow droplets. Lift, which is rising air, carries small droplets upward.
This end of the spray boom is equipped with nozzles that produce a very coarse droplet size, and this side has nozzles that produce a fine droplet.
Those fine droplets act like soap bubbles in the air, and are carried off-target by wind or rising hot air. Using coarser droplets gets more of the spray to the target. You may not see drift, but odds are it's happening.
The shorter the distance between nozzle and target, the less impact the forces have on the spray.
Don't get too close; nozzles need a minimal distance to create a uniform pattern.
Optimal distance is almost always indicated in the nozzle manufacturer's catalog.
This sprayer will produce fine droplets under high-powered lights to show you what you can't see during the day.
It's just as dramatic when you're using a boom sprayer.
Under the Pesticides Act, spray drift is illegal. Here's what happens when glyphosate is sprayed beside a tomato field: it can result in crop damage, yield loss, harvest delays, crop refusal and bad relations.
Drift damage to a permanent or multi-year crop, such as a vineyard, orchard, ginseng garden or greenhouse, can be evident for numerous years.
You can't change the weather, but you can adjust for it. Drift potential heightens as wind speed increases so high speed or gusting winds should be avoided.
Absolute calm conditions are not ideal for spraying either; fine droplets may stay aloft.
There is no sprayer, product or management strategy that is drift-proof. However, by understanding the causes of spray drift, following label guidelines, selecting appropriate equipment and making adjustments, the potential risk is significantly reduced.

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