Keep herbicide applications on-target

By Lizabeth Stahl and Jeffrey Gunsolus, University of Minnesota Extension

ST. PAUL, Minn. (4/28/2008)  Keeping herbicide applications on target is always a good thing, from your neighbor’s perspective as well as from control, economic, health and environmental standpoints. Drift management strategies help minimize pesticide movement off-target. 

Drift potential is significantly affected by the type of nozzle used in a pesticide application.  Nozzle type will influence spray droplet size, measured in microns, as well as the range of droplet sizes produced in an application. Droplets smaller than 200 microns in size can travel long distances due to their light weight and can drift off-target a considerable distance.

The type of product you are applying will determine what droplet size to target for adequate control. For example, if you are applying a “contact” herbicide, or a herbicide that does not move well within the plant, smaller droplet sizes and good coverage are needed for adequate control. Insecticide and fungicide applications also generally require smaller droplets sizes and good coverage for adequate control. Fine to medium-sized droplets, ranging from an average of 150 to 350 microns in size, are generally used for these applications.    

In comparison, a “systemic” herbicide moves within the plant to untreated tissue after application. As a result, coarse droplets, ranging from an average of 350 to 450 microns in size, can be targeted. Glyphosate, the most commonly used herbicide today, is a systemic herbicide.  Glyphosate moves to the growing points in treated plants after application. Because of this, drift-reducing nozzle technologies that produce larger droplets with a smaller percentage of fine droplets can be effectively used to help minimize drift potential when applying glyphosate.

Examples of drift-reducing technologies include pre-orifice, turbulence chamber, and venturi or air induction nozzles. Be sure to consult with the nozzle manufacturer’s information and product label when determining the correct nozzle type, droplet size, spray volume and pressure to use for your application. 

Adding a drift retardant to the tank is another option to help minimize drift. Research conducted by the University of Nebraska in 2006 by Johnson and colleagues, however, found drift-reducing nozzles were more effective at reducing off-target drift and that it would be less expensive to replace nozzles with drift-reducing nozzles than to use a drift-retardant throughout the growing season. 

Factors such as boom height, spray pressure and wind conditions at application also influence particle drift. To help reduce drift consider the following:

• Adjust your boom height as low as you can, while still providing uniform application
• Operate on the low end of the recommended pressure range
• Avoid applications when wind speeds are over 10 miles per hour as well as under dead-calm conditions or when a temperature inversion exists
• Increase spray volume as well as nozzle size to create larger droplets.  

Any use of this article must include the byline or following credit line:
Lizabeth Stahl is a crops educator and Jeffrey Gunsolus is a weed scientist; both are with University of Minnesota Extension

Media Contact: Catherine Dehdashti, U of M Extension, (612) 625-0237, ced@umn.edu.

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