Industrial agricultural sprayer in the fields

Keeping crop protectants on target continues to be at the forefront of growers’ minds as well as the minds of people neighboring the farms.

Recently I had the opportunity to observe drift damage on a neighboring farm where the Gramoxone spray droplets traveled over 500 feet from the target and did significant damage to the neighbor’s cover crop.

Making sure the product stays on the intended target is critical for the health of the plant as well as those surrounding the area.

As most already know, wind often can derail your plans to spray. Keep in mind the objectives of any spray application are to balance productivity, efficacy and prevention of off-site movement of pesticides.

It is also challenging to find a functional intermediate between controlling drift and not sacrificing herbicide (or other crop protectant) coverage and efficacy.

Any change that is made to the spraying system (nozzle selection, ground speed, pressure, pesticide formulations and adjuvants, e.g.) will ultimately affect droplet size, drift potential, and possibly efficacy.

Preventative Measures

In some situations, reducing spray drift can be easier said than done.

Extension agronomist Dwight Lingenfelter offers these steps to help you keep your product on target.

Spray during low wind velocities (3 to 10 mph). In general, winds are less of an issue early in the morning or late in the evening.

Read the label carefully. For example, the labels for new dicamba products (such as Engenia and XtendiMax) call for applications between one hour after sunrise until two hours before sunset to help reduce drift issues, while the Liberty (glufosinate) label recommends it is best to apply between dawn and two hours before sunset for optimal weed control.

Reduce spray pressure. Low pressures allow for larger droplet sizes.

Be aware that nozzles can produce different droplet sizes at different pressures. So, a nozzle might produce medium droplets at a low pressure but fine droplets at higher pressures.

However, some of the new drift-reducing nozzles are designed to require higher pressures for better spray coverage but still produce less drift than other types of nozzles.

In most cases, contact herbicides such as Gramoxone, Liberty, Reflex and Cadet should be applied through nozzles that produce medium to coarse droplets; thus, some of the newer drift-reducing nozzles might not provide the best spray coverage for effective weed control.

However, increasing the spray volume can help to improve coverage.

Another step is to increase carrier volumes or application rates. If possible, use 20 gallons or more per acre instead of 10 gallons or less per acre.

Use low spray boom heights. Make sure to use nozzles that have a spray angle of 110 degrees or more. This will allow the boom to be lowered more than it would for nozzles with lesser angles but will ensure spray pattern and proper overlap is maintained.

In general, for a boom with 20-inch nozzle spacings, maintain a boom height of 24 inches or less above the crop canopy.

You should also reduce sprayer ground speed (less than 10 mph). Faster speeds will cause the boom to bounce and spray vortex to occur, sending spray droplets higher than necessary into the air.

Use drift retardants. There are many good products on the market for this purpose, though some are not compatible with certain drift-reducing nozzle types.

Spray when the wind direction is away from sensitive crops and homes.

Consider including buffer zones if sensitive crops are in adjacent fields. A buffer could be 250 to 300 feet near sensitive areas.

If the buffer is part of the production area, treat the buffer with different products that will not affect the sensitive crop, or spray that area during a different timeframe to avoid injuring the sensitive crop.

Another option is to plant a cover crop in the buffer zone so there will not be an issue if it’s injured or killed by spray drift.

Finally, invest in “high-tech” sprayers (e.g., pulse width modulation). Some of the new sprayers use a pulsing system to assist in better application and drift reduction.

Keep in mind, however, that some of the new sprayers increase pressure to maintain output if the ground speed is increased, thus producing additional fine droplets.

Leon Ressler is a Penn State Extension educator based in Lancaster County, Pennsylvania.


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