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Spray
Drift
Compliments of
Agronomy Services Department
Spray drift wastes an expensive input and may
result in reduced pest control that cuts yield or necessitates another
application. Losses or costly litigation may also result if sensitive crops
in adjacent fields are damaged. Now is the prime time for spray drift
problems because post emergence applications are in full swing. Herbicides
such as Banvel; Clarity; Distinct, and 2,4-D especially with the ester
formulation, may reach the targeted weed, but the chemical often vaporizes
in hot, humid weather. The vapors can then drift and cause damage in a
process called volatilization. Ideally spraying should be done when
temperatures are below 80 F and humidity is low. Improved spraying
technologies can help reduce drift, but wind remains the most influential
factor.
Manufacturers are designing
equipment to help control drift. Among these improvements are low-drift
nozzles. Small droplets drift more than larger, coarser ones, so use
nozzles that produce the largest effective droplet size. Keep several
nozzle types on the sprayer boom and change nozzles in accordance with
wind speed changes.
Air-assisted sprayers can
reduce drift of smaller droplets by using air to replace part or all of
the water carrier. Some air-assist systems atomize the spray solution,
while others use a high-velocity airflow to transport the spray mixture to
the target. Also relatively new are sprayers that produce
electrostatically charged droplets with an electrical charge opposite that
of plants. The opposites charges attract, creating a magnetic attraction
between the herbicide and plants.
Spray additives or
"drift retardants" can help keep the pesticide on target. Drift
retardants increase viscosity, which helps to enlarge droplets to the
larger range of the nozzle's spectrum while reducing the portion of the
spray volume contained in small, drift-prone droplets. Larger droplets are
more likely to stay on target.
With 40 retardants on the
market, choosing the right one can be challenge. The Ohio State University
recently tested about a half dozen products and found they all had the
desired effect on droplet size, but they were not equally effective due to
differing amounts of active ingredients. To make the right choice, check
the concentration of the active ingredients. If two products have the same
price, buy the product with the highest concentration of active
ingredient.
Here are some other
drift-reducing principles to consider:
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Shielded sprayer booms or nozzles can
effectively direct small, drift-prone droplets toward the ground.
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Increasing pressure reduces droplet
size, so keep pressures at the low end of the recommended range.
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Don't spray on very hot, dry and windy
days, especially near sensitive vegetation. Although it may be
impractical, night is the best time to spray. If that's not possible,
spray in the morning or late afternoon.
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Avoid spraying when sensitive crops are
downwind. Leave a 50-foot to 100-foot buffer strip; spray later when
the wind shifts.
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