Reducing Pesticide DriftThis information comes from "Reduce
Pesticide Drift", PIP-35, Prepared by Robert G. Bellinger, Pesticide
Coordinator, P. Mac Horton, & Clyde S. Gorsuch, Extension Entomologists
(Rev. January 1996)
is a side effect of pesticide use associated with ground and aerial application
and is an important environmental concern. Drift is the uncontrolled airborne
movement of spray droplets, vapors, or dust particles, away from the intended
point of application. While drift in agricultural and forest situations is
more commonly thought of, drift may also occur indoors in air currents caused
by ventilation systems and forced-air heating and cooling systems. All drift
is illegal and can cause potential injury to non-target plants and animals,
and has the potential for producing illegal residues on non-target sites.
every pesticide application produces some amount of drift. How much drift
occurs depends on such factors as the formulation of the material applied,
how the material is applied, the volume used, prevailing weather conditions
at the time of application, and the size of the application job.
applications which are directed upwards or made by aircraft are the most
likely to be subject to drift. Pesticide application by aircraft can result
in residue problems on sites that are distant from the actual application
site. Pesticides released close to the ground or substrate are not as likely
to be suspended in the air as those released from a greater height or distance
from the target.
particles, especially dusts and low volatility vegetable oils, are very easily
carried by air currents. Heavier formulations such as granules and pellets
settle out of the air very quickly. High pressures and small nozzle openings
produce very fine spray droplets with accompanying high drift potential.
Lower pressures and larger nozzle openings produce coarser sprays with larger
droplet sizes having less drift potential.
and nonfumigant pesticide formulations having a high vapor pressure (are
volatile) may produce vapors. Vaporization (volatilization) increases as:
air and surface temperatures increase; relative humidity decreases; particle
or droplet size decreases; and air movement increases.
control is your responsibility! In fact, many labels specify that drift control
is the responsibility of the applicator. Drift cannot be completely eliminated, but it can be greatly reduced.
Rules for ground applications
- Use as coarse a spray as
possible and still obtain good coverage and control. For sprays, use
formulations which give large diameter (150 - 200 microns or larger)
spray droplets. Droplet size is one of the most important factors
affecting drift, however, addressing droplet size alone is not
sufficient to reduce the probability of drift and potential damage.
- Don't apply pesticides
under windy or gusty conditions; don't apply at windspeeds over 15 mph,
ideally not over 5 mph. Read the label for specific instructions.
- Maintain adequate buffer zones to insure that drift does not occur off the target area. Read the label.
- Be careful with all
pesticides. Insecticides and fungicides usually require smaller droplet
sizes for good coverage and control than herbicides, however,
herbicides have a greater potential for non-target crop damage.
- Choose an application
method and a formulation that is less likely to cause drift. After
considering the drift potential of a product/formulation/ application
method, it may become necessary to use a different product to reduce
the chance of drift.
- Use drift control/drift
reduction agents. These materials are basically thickeners and are
designed to minimize the formation of droplets smaller than 150
microns. They help produce a more consistent spray pattern and aid in
deposition. Some of these are: Chem-Trol, Intac, Lo-Drift, Nalco-Trol,
Nalco-Trol II, StaPut, Wind-Fall, Arborchem 38-F.
- Choose the formulation carefully.
Water-based sprays will volatilize more quickly than oil-based sprays. However,
oil- based sprays can drift farther because they are lighter, especially
above 95° F.
- Apply pesticides early in the morning or late evening; the air is often more still than during the day.
- Don't spray during thermal inversions,
when air closest to the ground is warmer than the air above it. When possible,
avoid spraying at temperatures above 90°-95° F, ideally not over 85° F.
- Know your surroundings!
You must determine the location of sensitive areas near the application
site. Some crops are particularly sensitive to herbicides which move
off-site. Homes, schools, hospitals and other care facilities, surface
waters, water treatment facilities, etc. are considered sensitive
areas. Be aware of the location of seasonally flowering crops and the location of honey bee colonies.
You should know the location of sensitive areas within a one-half mile
radius of sites on which you would make, or have someone else make,
pesticide applications, and one mile downwind. Make pesticide
application decisions with these locations in mind.
- Don't apply pesticides
near lakes, reservoirs, ponds, rivers, streams, marshes, etc. Add a
drift retardant on fields near any water source! Read the label for
- Use a solid cone or fan spray nozzle. These produce larger droplet sizes than hollow cone nozzles.
- Be sure you are getting the spray deposition pattern you think you are; service and calibrate your equipment regularly.
- Check your system for leaks. Small leaks under pressure can produce very fine droplets.
- Determine wind direction
and take this into account in determining application timing, equipment
and whether or not to make an application. The wrong wind direction can
cancel out everything else you have done to reduce drift.
- When chemigating, turn off the end gun. Use drop booms instead of upwardly directed nozzles.
Rules for aerial applications
- For applications of
liquid and dry formulations, commercially available or homemade shrouds
or skirts attached over or behind the application equipment can help
prevent spray droplets and pesticide particles from becoming airborne.
- Using air blast sprayers
in orchards is a highly visible application method with significant
potential for drift problems. Be sure the machine is properly adjusted
to direct the spray into the tree canopy. On most sprayers, one or more
of the upper nozzles will not deliver spray to the tree and should be
shut off. Use only the nozzles that actually deliver spray to the tree.
- In orchards or in shade
tree plantings, whenever possible, cut off the spray for missing trees
in the row. Spray that does not enter the tree canopy is wasted and
contributes significantly to drift problems. Reducing drift saves you
money by reducing the amount of spray material needed.
- For ground rigs and hand
sprayers, use low pressures and don't spray too close to the target
surface to reduce spray-back aerosol.
- For applications by PCOs,
lawn care technicians, homeowners, etc. be sure windows, doors, and
foundation vents of nearby buildings are closed. Know where ventilation
system intakes are relative to your spray application. Be sure windows
of nearby parked vehicles are closed.
- Be careful of applications near painted surfaces or other non-target surfaces.
- As an added precaution,
remove articles within and adjacent to the application area which may
become contaminated, such as: lawn furniture, recreational equipment,
pet or livestock feeding items, and removable housing and bedding
materials. Remove animals.
Remember, ALWAYS read and follow label directions.
- Try to get good field-end
coverage on initial spray runs; crossing the ends of fields which are
bordered by trees or other obstacles usually means flying higher and
increasing the chance of drift.
- Fly slow. Fly low. Slow
speeds are combined with lower pump pressures to produce larger
droplets. Herbicides should be applied at a lower height than other
- For fixed wing aircraft, don't use a whirl-plate, rather, use a 1/16 to 1/18 inch diameter orifice plate directed straight back.
- Be sure the positive shut-off is working properly, and use it!
- Nozzle orientation
affects wind shear across the nozzle face, and subsequently droplet
size. Use a nozzle orientation that will give the desired droplet size.
- Boom length should be no
more than 75% of the wingspan of fixed wing craft, or of the rotor
diameter on helicopters to reduce drift caused by wingtip and rotor
- Use Microfoil boom, Tru-Value boom or equivalent drift control system. See the pesticide label.
- When there is any
possibility or concern of drift, use a drift retardant as a standard
part of your spraying service. Using drift retardants can promote a
positive environmental concern and help eliminate legal problem.