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Avoid Herbicide Drift and Damage to Susceptible Crops or Plants

PULLMAN, Wash. – Herbicide applicators are responsible for managing and controlling off-target drift. As spring – and one of the two times of year when drift is most likely to occur – approaches, Washington State University Extension educators are offering some advice about how to avoid herbicide drift.

Drift reduces herbicide efficacy and may cause significant damage to nearby crops or ornamental plants, impact fish and wildlife, and contaminate water resources. Herbicide drift can also deposit illegal residues on edible crops, rendering them unsalable.

Grapes, blueberries, caneberries, and nursery crops are especially sensitive to several herbicides used in agronomic crops, pasture and rangelands, forests and right of way areas. These include the sulfonylurea herbicides (Group 2), phenoxy herbicides and dicamba (Group 4), and glyphosate (Group 9). When applied with equipment set up incorrectly or under poor weather condition, herbicides can drift to sensitive areas and cause significant injury. If injury is severe enough, or occurs repeatedly, it can cause reduced yield, poor crop quality and, occasionally, plant death. Drift injury can result in a substantial economic loss to other crops such as canola, peas, chickpeas or specialty broadleaf crops grown for seed.

Herbicides can move either as droplets as they are dispensed from the sprayer or, for some formulations, as vapors after application.

To manage spray droplet drift, pay particular attention to labels for droplet size requirements and set up your equipment to ensure drift minimization. Select an appropriate nozzle type and pressure and buy new ones if needed. Also, be aware of weather conditions, as low velocity winds and temperature inversions can result in drift problems. Temperature inversions occur when warmer, less-dense air moves over cooler, denser air. Temperature inversions create subtle horizontal air flows that can move concentrated amounts of spray long distances. Inversions may occur at any time, but are typically prevalent starting before dusk and lasting until after sunrise.

To manage for vapor drift, heed herbicide label precautions for air and surface temperatures of treated areas.

The Washington State Department of Agriculture has statewide and county-based herbicide regulations to help address drift. Be aware of herbicide regulations in your county. There are cut-off dates and times as well as formulation prohibitions. If using air induction nozzles at their recommended spray pressure, obtain the blanket permit from WSDA. Air induction nozzles are a great drift-reduction technology and WSDA herbicide regulations were written prior to their invention.

In addition to statewide and county-based herbicide regulations that address drift, some herbicide labels have added buffer strip requirements between the application area and the closest downwind edge of sensitive habitats. Be sure to read and follow all label requirements related to drift management.

The herbicide applicator has ultimate control of drift management. Know what is around the application site and recognize all sensitive areas for plants, wildlife and people. Select the best product for the situation in order to minimize the potential for crop injury nearby. Set up the spray equipment to manage spray drift; use medium or coarse sprays. Calibrate the sprayer and assess the spray pattern for uniformity. Recognize the current weather patterns and be cautious if applying with wind under 3 mph. Under 3 mph, it is impossible to predict where small droplets will drift. If there is an inversion, droplets can travel in a concentrated mass for a long time, thus impacting sensitive plants over long distances.

Grape growers concerned about herbicide drift should familiarize themselves with WSU’s leaf-indexing system to assist with investigation of plant damage; visit http://bit.ly/wsu-leaf-index for more information. Without leaf indexing, investigations are nearly impossible.

Finally, remember that with any pesticide application, it is important to be aware of people who may be in the vicinity or who could travel near the application site. Take whatever precautions are needed to make sure no one is exposed to pesticide spray.

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NOTE: Please download and play on air this brief PSA about minimizing herbicide drift: herbicide drift PSA 1.

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Media Contacts

Drew Lyon, WSU Extension weed specialist, 509-335-2961