What is Pesticide Drift?
Pesticide drift is "...the movement of pesticides through the air outside a targeted area." according to the Wisconsin Pesticide Applicator Training Manual: Turf & Lanscape, Commercial Catagory 3.0 (Sixth Edition)
Pesticides can drift in two ways. One way is particle drift, which is the movement of small spray droplets that are produced at the time of application. The other type of drift is vapor drift caused by the movement of pesticide vapors (fumes) after a volatile pesticide is applied. Vapor drift occurs when a volatile pesticide changes into gas fumes that travel over a non-target area. Vapor drift can be carried over great distances under certain weather conditions.
It is illegal in the state of Wisconsin for pesticides to drift to a non-target area. Many other states and countries have such laws, but enforcement remains difficult. Applicators need to be truly concerned about protecting themselves, others, and the environment from pesticide drift.
Dangers of Pesticide Drift
Pesticide drift is a serious matter and a major cause of contamination within the environment. Many blame agriculture for excessive use of pesticide, but lawn care application contributes much more than agriculture applications. Drift can cause damage to non-target areas. Significant drift and pesticide exposure can harm animals, plants, and people as well as contaminating water sources and soil. Drift from insecticides and fungicides can easily go unnoticed unless residue is visible. The effects of herbicide drift are often very apparent upon contacting vegetation.
Mild pesticide poisoning symptoms include fatigue, weakness, dizziness, blurred vision, nausea, vomiting, irritation of skin, eyes, and airways, nervousness, stomach cramps, and diarrhea.
Severe pesticide poisoning symptoms include fever, intense thirst, unconsciousness, constricted pupils, convulsions, loss of breath, coma, and even death. Pesticide poisoning can be confused with heat stress and heat stroke.
Contact emergency services and the Poison Control Center immediately when experiencing symptoms during or after pesticide exposure. Always use proper protective equipment when applying pesticides and always be aware of people and animals in target and surrounding areas.
Wind speed and direction are very important when it comes to reducing pesticide drift. Do not spray when windy, despite the direction of the wind. Even a light wind causes drifting. Spraying in the early morning or evening is usually best since wind speed is lowest during these times.
Spraying right before a rain shower will cause pesticide run-off. Run-off is not considered drift but is still important to note. Run-off causes pesticides to leave application site and is generally prohibited.
Temperature inversion occurs when the air temperature near the ground is cooler than the air above. This usually occurs when the ground rapidly cools. The cooler air near the ground tends to stay in a layer that is lateral to the surface. These conditions provide the greatest chance of drifting, because spray droplets remain in the cool air layer just above the surface. Temperature inversion can be observed by watching the steam/smoke emissions of power plants during a calm morning. Inversion will cause the emissions to condense instead of continuing to rise and disperse.
Vertical air movement occurs when air near ground level becomes warmer than air above. Spray droplets can be carried up into the sky via warm air and carried for several miles. Wind added to the scenario will cause droplet size and drift distance to increase. Avoid spraying on hot and windy days, especially summer afternoons.
Humidity & Temperature
Low humidity and high temperatures increase evaporation rate of droplets. Evaporation reduces droplet size which increases the possibility of drifting. Evaporation also removes water from the droplet, which causes the droplet to contain a concentrated amount of pesticide. High temperatures also cause small droplets to turn into vapor.
Fall Rate of Droplets
Time to Fall 10 Feet in Still Air
Drift Distance with Wind (10 mph)
Pesticide Drift Control
How far a particle of pesticide can drift largely depends on the size of the particle and its specific gravity. The smaller and lighter the particle, the further the drift. Small droplets remain in the air longer and are carried easier by wind.
Small handheld sprayers produce less drift compared to a vehicle-mounted boom sprayer. Homeowners will produce must less drift compared to commercial pesticide applicators. Care still must be taken whether a homeowner applicator or a commercial applicator.
Increasing the pressure of a sprayer will create smaller droplets that are susceptible to drifting. Using low-pressure fan nozzles allow the applicator to maintain desired coverage compared to standard and high-pressure nozzles.
The type of nozzle used when spraying pesticides influences drift. Conventional nozzles can be adjusted to allow a very fine spray or large droplets. Flood and drift-reduction nozzles greatly reduce drift. Spray is effected by the sprayer's nozzle opening as well. Particles become smaller as the size of the nozzle opening decreases.
Carriers and Adjuvants
Thickening agents can be used to reduce drift, but drifting will not be entirely prevented. Precautions still need to be taken to reduce drift. Larger droplets will reduce drift, but coverage will be reduced. Be sure to check adjuvants for compatibility with application pesticides.
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