Avoiding herbicide drift

Drift occurs in two ways: Through particle drift and vapor drift.

Particle drift

Particle drift occurs when small spray droplets travel long distances during periods of high wind and droplets blow from the targeted site. To avoid this, use larger spray droplets with low pressure, and only apply herbicides when wind speed is low.

Vapor drift

Vapor drift occurs when products volatilize or evaporate and move off the application site. As temperatures rise into the upper 80s and 90s, the volatility of some products increases.

Product labels provide information on when it's not safe to apply the product based on certain temperatures. Vapor drift potential is highest when conditions are hot and dry.

Nozzle selection is critical to reducing pesticide drift. The nozzle directly affects spray droplet size, which is the major factor influencing herbicide drift.

The pesticide label may require using specific nozzles that produce a coarse- or medium-sized droplet. Coarse droplets reduce drift, lowering drift potential.

Nozzle examples

Small droplets take more time to fall to the ground, which can cause them drift farther. 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 the amount of drift. Examples of such nozzles are:

• Turbo TeeJet and AIXR TeeJet nozzles from Spraying Systems Co.
• Hypro Ultra Lo-Drift and GuardianAir nozzles.
• TurboDrop nozzles from Greenleaf Technologies.

Select the right nozzle for the product

When using nozzles that produce larger droplet sizes, keep the type of product you’re working with in mind.

Target a coarse-sized droplet for the appropriate pesticides such as a systemic herbicide like glyphosate. Effectiveness can be hindered if you apply contact herbicides, insecticides and fungicides in a coarse-sized droplet.

Also consider spray boom height. The higher the boom, the higher the drift potential. Keep the boom only as high as it needs to be for adequate coverage and sprayer operation.

Boom height depends on nozzle angle and spacing. For example, 110-degree nozzles at 20-inch spacing should be 15 to 18 inches above the target to produce a uniform application rate across the length of the boom. To minimize spray drift potential, maintain a boom height of 24 inches or less above the crop canopy.

To reduce off-target movement, decrease the distance spray droplets travel to reach the target.

Lower pressures allow for larger droplet sizes. Know that nozzles can produce different droplet sizes at different pressures. A nozzle might produce medium droplets at a low pressure but fine droplets at higher pressures.

Reducing pressure requires recalibration and adjustments to sprayer speed and carrier volume (gallons per acre).

Always measure wind speed and direction before, during and after the application.

Always follow label information, although generally, wind speeds of 3 to 7 miles per hour (mph) are preferable. Spray at low wind velocities (less than 10 mph).

If wind speed or direction changes during an application, immediately adjust the buffer size or location or stop the application.

Applying pesticides during a temperature inversion – which does occur in Minnesota – can cause 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’s no mixing of the air. Spray droplets aren’t dispersed, but stay 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.

When appropriate, use drift retardants. There are many good products for this purpose. However, some aren’t compatible with certain drift-reducing nozzle types, so ask your suppliers.

Consider including buffer zones if adjacent fields have sensitive crops. Some labels require a 30-foot downwind buffer in the direction the wind is blowing. Other labels recommend a buffer of at least 250 to 300 feet near sensitive areas.

Applicators are required to follow the label. Because requirements differ from label to label, you must read the individual label to be in compliance.

If the buffer is included as part of the production area, treat the buffer with different products that won’t affect the sensitive crop and/or spray that area during a different time frame. This helps avoid injuring the sensitive crop. Another option is to plant a cover crop in the buffer zone so there won’t be an issue if it’s injured or killed by spray drift.

The Minnesota Department of Agriculture doesn’t seek compensation on behalf of parties or entities. They do, however:

• Answer questions.

• Investigate formal complaints.

• Visit sites.

• Review documents.

• Enforce regulations.

Documentation can help resolve questions about potential drift issues. Consider doing the following:

• Record dates.

• Collect information on wind speed and direction.

• Inquire about the applied product.

• Take photos of the injury.

The Minnesota Department of Agriculture receives approximately 150 pesticide-related complaints per year. Approximately 66 percent of cases warrant an investigation. Of those, 25 to 30 percent are closed without action because allegations of pesticide drift or misuse couldn’t be substantiated.

From 2012 to 2014, about 30 percent of all complaints were related to pesticide drift. A number of complaints involve lawn care applications in urban settings. Of the total complaints annually received, approximately 40 percent result in financial penalties.