No. 5 Article 7/April 28, 2006

Windy Conditions and Herbicide Applications

Looking back through previous years' issues of the Bulletin, I find it's been about four years since we've mentioned much about herbicide drift, though the problem remains with us. Soil conditions in many areas of the state are favorable for corn planting, but windy conditions always are much less favorable for herbicide applications. Pesticide applications made when wind speeds are sufficiently high favor off-target movement and are obviously not advisable.

Spray drift is a function of droplet size and wind speed. Spray droplet size is primarily determined by nozzle type and size and by spray pressure, but it can also be influenced by air temperature and relative humidity. Smaller spray droplets are more prone to move outside the intended target area than are larger droplets, but even large spray droplets can move outside the target area when applied during windy conditions. Much interest has recently been focused on drift reduction nozzle technology as well as utilizing drift reduction agents to reduce spray drift. While these technologies can change droplet size and reduce spray drift, they may give a false sense of security leading to applications made when wind speeds are, in reality, too high.

We understand that with the number of acres covered by commercial applicators, applications are sometimes made under less than ideal conditions. However, few "good things" come from herbicide drift complaints, not to mention the potential weed control problems if too much of the herbicide moves out of the intended target area. Increasing gallons of carrier per acre and lowering spray pressures are two options to help reduce the possibility of drift. Precluding drift may require keeping the sprayer in the shop until the wind dies down.--Aaron Hager and Dawn Nordby

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