June 19, 2020
As they say, “With much power comes much responsibility,” and the various herbicides, fungicides, and insecticides that growers have in their toolbox for managing their crops are indeed powerful tools. These pesticides also have inherent risk when it comes to their movement off target whether it be through drift caused by decisions made by the applicator or just bad luck caused by an unpredictable shift in the weather. In any case, if you observe damage, it’s important to respond appropriately.
To reduce or eliminate pesticide drift, use the following tactics.
1. Select the right nozzle for the job
No one nozzle will be the best for all spraying conditions, although some work well over a range of uses. To determine which nozzle may be best suited for the intended use, first consult the pesticide label for specific nozzle types, carrier rates, droplet sizes, and drift precautions. An example label statement would be: “Apply with 15 or more gallons per acre using a nozzle producing a medium droplet.”
Nozzle selection and pressure should be based on the nozzle manufacturer’s droplet size category charts. Typically, low-drift nozzles will produce spray droplets in the coarse to ultra-coarse range, and minimal droplets in the fine range (which are more likely to drift). Higher spray volumes may also allow the use of larger nozzle orifices (sizes) which produce coarser spray droplets.
Small droplets take more time to fall to the ground and can thus drift farther. It is desirable to use a nozzle that produces large, uniform droplets. Switching from standard flat-fan nozzles (such as an XR11003) to turbulence-chamber or venturi nozzles, increases droplet size and can greatly reduce drift potential. Examples of such nozzles are the Turbo TeeJet and AIXR TeeJet nozzles (Spraying Systems Co.), Hypro Ultra Lo-Drift nozzles, and TurboDrop nozzles (Greenleaf Technologies).
Keep in mind the type of product you are working with when using nozzles that produce larger droplet sizes. Target a coarse-sized droplet for appropriate pesticides such as a systemic herbicide like glyphosate. The effectiveness of contact herbicides, insecticides, and fungicides can be hindered if applied in a coarse-sized droplet.
The American Society of Agricultural and Biological Engineers (ASABE) developed a droplet size classification system (ASABE S-572.1) that ranges from extremely fine to ultra coarse, based on measurement in microns. One micron equals one thousandth of a millimeter. The droplet size category recommended for use with a particular pesticide may be listed on the product label.
2. Reduce spray pressure
Lower spray pressures allow for larger droplet sizes. Be aware that nozzles can produce different droplet sizes at different pressures. Therefore, a nozzle might produce medium droplets at a low pressure but fine droplets at higher pressures. Reducing pressure may require recalibration and adjustments in sprayer speed and carrier volume (gallons per acre).
3. Monitor wind speed and direction
Always measure wind speed and direction before and after an application. Always follow label information, but in general, wind speeds of 3 to 10 mph are preferable. Make applications at low wind velocities (less than 10 mph). If wind speed or direction changes during an application, immediately adjust the buffer size or location as needed, or stop the application. The best investment you can make is to buy a wind meter that tells you how high the wind velocity is at any given time. Having a wind meter handy will help you avoid a costly problem associated with spray drift.
4. Lower boom heights to reduce drift
A wider spray angle allows the boom to be placed closer to the target (not the soil when spraying weeds post-emergence). The higher the nozzle is above the crop or target, the more opportunity for the wind or air flow to move droplets from the intended site. Spray equipment operated at high speeds can create turbulence in the airflow around the machine that can catch small droplets and make them vulnerable to drift. Determine the optimum boom height for a particular nozzle from nozzle literature to reduce drift potential. If boom height is set too low, uneven patterns in the application or skips may occur.
5. Avoid applications during a temperature inversion
Applying pesticides during a temperature inversion can result in damaging, long-distance drift. Inversions occur when warm air, which is light, rises upward into the atmosphere and cool air, which is heavy, settles near the ground. When cool air settles below warm air, there is no mixing of the air. Spray droplets are not dispersed, staying in a concentrated mass that can move off-target with any subtle airflow. Typically, temperature inversions start at dusk and break up with the sunrise because of vertical air mixing. Use caution when spraying at wind speeds less than 3 mph as a temperature inversion could exist. Refer to a University of Minnesota Crop E News “Temperature inversions: Something to consider before spraying” for more information.
6. Monitor temperature and relative humidity
As the air temperature increases and humidity decreases, droplets evaporate, become smaller and lighter, and travel further.
7. Know and follow application setbacks
Application setbacks and vegetative filter strips may be required on the labels of pesticide products in order to protect sensitive areas. Read pesticide labels carefully to see whether these practices are required. The downwind buffer areas required on the label may vary in size depending on the rate of the herbicide applied. To maintain a required buffer zone, no application swath can be initiated in, or into an area that is within the applicable buffer distance.
8. Use drift retardants when appropriate
There are many good products on the market for this purpose. However, some are not compatible with certain drift-reducing nozzle types so ask questions of your suppliers. Drift retardants can reduce drift risk and maximize pesticide performance by binding ultra-small spray particles into larger droplets.
To learn more about spray drift and drift prevention, refer to the University of Nebraska UNL Extension NebGuide Spray Drift of Pesticides.
An argument can easily be made that if you observe drift damage to your crops, you have a responsibility to report it. Reporting drift is important for several reasons, such as:
Ensuring that food and feed are safe when they enter commerce
Developing pesticide education and compliance assistance by the local Department of Agriculture that protects human health and our environment
Protecting people, such as workers, from exposure to potentially dangerous residues
Taking appropriate enforcement actions when pesticide violations occur
If you suspect drift, report it; complaints need to be filed within 45 days (in Minnesota) of when the event occurred for them to be investigated.
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