2005 Year in Review

From the Fields – Herbicide Application

Herbicide application to emerged corn and soybean is a common practice. Managing herbicide drift from these applications requires planning and using certain technology. Here are some tips for reducing drift and controlling weeds.

Use coarse droplets. Applicators should select nozzles that produce coarse droplets. Three such nozzles are the venturi, turbo flood, and turbo flat-fan.

Use low pressure. Use pressure in the lower portion of the nozzle’s recommended pressure range. Increasing spray pressure does not force droplets into the crop canopy; rather it creates smaller droplets with less momentum. An exception to this rule is the use of venturi (air-induction) nozzles, which are designed for high pressure.

Lower boom height. Wind velocity increases with height. Keep the spray boom at the minimum distance from the target (weed) while maintaining uniform coverage.

Use drift-reduction nozzles. Use nozzles designed to reduce drift. See above comments on coarse droplets.

Use drift-reduction agents. Drift-reduction agents increase droplet size. Be sure to read nozzle instructions and the herbicide label.

Spray when wind is less than 10 miles per hour. Drift increases with wind speed. However, spraying in completely calm conditions can result in off-target movement of the herbicide.

Increase spray volume. Increasing the gallons per acre with a larger nozzle size produces larger droplets.

Avoid sensitive areas. Keep a buffer, or no-spray zone, when spraying near sensitive plants, gardens, wetlands, etc. If appropriate, return to these areas when conditions are favorable for spraying.

Read the label. Herbicide labels provide application instructions that must be followed to make a safe and legal application.

Know your herbicide. All herbicides can drift as spray droplets, but some herbicides can volatilize to cause plant injury from the drift of vapors or fumes.

Pay attention to the weather. Low relative humidity and/or high temperature will cause more rapid evaporation of spray droplets between the spray nozzle and the target than will high relative humidity and/or low temperature. Evaporation reduces droplet size, which increases the potential drift of spray droplets.

Avoid spraying during an inversion when the air is very calm. Inversions commonly occur in the early morning and late evening. During an inversion, small droplets remain suspended and they can later be blown off target in unpredictable directions.

There are many resources for information on herbicide drift, one is the University of Illinois Pesticide Education website: Pesticide Safety.

by  Editor, theCity1.com
June 2, 2005