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Schmidt: Reducing spray drift and its effects

June 9, 2017
Yolanda Schmidt - County Agent , Pierce County Tribune

Herbicide spray drift during pesticide applications is an increasing concern in agriculture. Diversification of crops, more active and non-selective herbicides, and a greater awareness of pesticides in the environment have caused spray drift management to become every applicator's business even homeowners who make herbicide applications to their yards.

Spray drift is the movement of a pesticide through the air, during or after application, to a site other than the intended target. Drift may occur as vaporized active pesticide from the application site, but it is usually the physical movement of very small drops from the target area.

Each growing season numerous calls come into my office from both homeowners and landowners regarding pesticide drift situations. Pesticide spray drift always has been a costly and frustrating problem for applicators. It's particularly frustrating because some of the seemingly best weather conditions for pesticide application are often the worst. That is because those conditions are caused by air temperature inversions. Air temperature inversions provide near-perfect conditions for tiny, aerosol-size droplets to drift away from their targets.

Temperature inversions are micro-climatic events that can significantly contribute to off target movement of pesticides. A recent NDSU Extension Service publication explains in detail what inversions are, why they develop and dissipate, how they are impacted by land condition, how to identify them, how to measure them, and how to minimize their impact on pesticide applications. The publication, AE1705- "Air Temperature Inversions Causes, Characteristics and Potential Effects on Pesticide Spray Drift" can be found online at

Understanding inversions is essential to following state and federal regulations that prohibit pesticide application during inversions, observing pesticide manufacturers' warnings about inversion conditions on product labels and preventing unintended pesticide contact with non-target areas.

Private applicators using pesticides on their farm or ranch as well as in town homeowners should benefit from the comprehensive explanations found in publication AE1705 - "Air Temperature Inversions Causes, Characteristics and Potential Effects on Pesticide Spray Drift".

NDSU recommends the following to help minimize spray drift:

1.Wind velocity and direction: Apply when wind direction is away from susceptible plants, during low wind speed, and in the absence of temperature inversions.

2.Boom height: Adjust boom as close to the target as possible while maintaining uniform spray coverage. Choose nozzles with a wide angle as opposed to narrow angle nozzles.

3.Spray shields: Cones around nozzles reduce drift by 25-50% and spray shields that enclose the entire boom reduce drift by 50 to 85%. Spray shields should not be used as a substitute for other drift control techniques but as a supplement to drift reduction.

4.Drift control: Reduce drift by increasing droplet size, reducing spray pressure, using drift reduction nozzles, adding drift reducing additives that do not increase spray viscosity, and orientating nozzles rearward on aircraft.

5.Drift-reducing nozzles: Sprayer nozzles designed to reduce spray drift increase spray droplet size and reduce the number of small droplets (fines). Two primary types of drift-reducing nozzles have pre-orifice and air-induction (venturi) designs.

6.Herbicide formulation: Some herbicides have been formulated to reduce drift. Amine formulated herbicides are less volatile than ester formulations. 2,4-D is formulated as an acid, ester, and various amine salt. Dimethyl amine (dma) formulations of dicamba and ester formulations of 2,4-D and MCPA may volatilize at 70 to 90 F and cause plant injury from vapors. Amine formulations of 2,4-D and MCPA are non-volatile at high temperatures. Soil surface temperature is much warmer than the air. Herbicide vapor can drift farther and over a longer time than spray droplets. Volatile herbicides should not be used near susceptible plants.

Additional information on control of spray drift and field investigation of crop injury can be found in the NDSU Extension publication W-253, "North Dakota Weed Control Guide" which can be obtained at your local NDSU Extension office.

Chemical Cost Share Distribution

The Pierce County Weed Board chemical cost/share program will be distributing Tordon and Plateau Monday, June 23rd from 8:00 a.m. - 12:00 p.m. at the Pierce County Weed Board Building. Those participating MUST have and present a valid private pesticide applicator's license when purchasing restricted use pesticides (i.e. TORDON).

For more information on the chemical cost/share program call the Pierce County Auditor's office at 776-5225.



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