Understanding Spray Drift

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Understanding Spray Drift
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Why Interest in Drift?

• Wasted chemicals
• Off-target damage
• Less tolerant neighbors
• Litigious Society
• Environmental impact
• Water and Air Quality
• Public more aware of pesticides
• (Negative) (Perceptions)
• Urban sprawl

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Nozzle Technology?

• Nozzles designed to reduce drift
• Improved drop size control
• Emphasis on Spray Quality

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Nozzles are important

• Control the amount GPA.
• Determine uniformity of application.
• Affects the coverage.
• Influences the drift potential.

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Nozzles drift

• Creating smaller spray drops will result in
  increased drift.

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Technical Aspects of Spray Drift
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Definition of Drift

• Movement of spray particles and vapors
  off-target causing less effective control and
  possible injury to susceptible vegetation,
  wildlife, and people.
• Adapted from National Coalition on Drift
  Minimization 1997 as adopted from the AAPCO
  Pesticide Drift Enforcement Policy - March 1991

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Types of Drift

• Vapor Drift - associated with volatilization
  (gas, fumes)
• Particle Drift - movement of spray particles
  during or after the spray application

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Factors Affecting Drift

• Spray Characteristics
• chemical
• formulation
• drop size
• evaporation

• Equipment Application
• nozzle type
• nozzle size
• nozzle pressure
• height of release

• Weather
• air movement (direction and velocity)
• temperature and humidity
• air stability/inversions
• topography

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Wind Direction

• Wind direction is very important
• Location of sensitive areas?
• buffer zones.
• Do not spray if blowing towards sensitive areas
• all nozzles can drift.
• Spray when breeze is gentle, steady, and blowing
  away from sensitive areas.
• Dead calm conditions are never recommended.

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However, Drift Potential May be High at Low Wind
Speeds

• Because
• Light winds (0-3 mph) tend to be
• unpredictable and variable in direction.
• Calm low wind conditions? - temperature
  inversion
• Drift potential is lowest at wind speeds between
  3 and 10 mph (gentle but steady breeze) blowing
  in a safe direction.

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Wind Current Effects

• Wind currents can drastically affect spray
  droplet deposition
• Structures drastically affect wind currents
• Wind breaks
• Tree lines and orchards
• Houses and barns
• Hills and valleys

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Wind Patterns Near Treelines
Adapted from Survey of Climatology Griffiths and
Driscoll, Texas AM University, 1982
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Wind Meters and Compass
Prices for Wind Meters taken from Gemplers 2000
Master Catalog Plastimo Airguide Inc., 1110
Lake Cook Road, Buffalo Grove, IL
60089(708-215-7888)
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Inversions
Under normal conditions air tends to rise and mix
with the air above. Droplets will disperse and
will usually not cause problems.
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Temperature Inversions
Under these conditions the temperature increases
as you move upward. This prevents air from
mixing with the air above it. This causes small
suspended droplets to form a concentrated cloud
which can move in unpredictable directions.
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Recognizing Inversions

• Under clear to partly cloudy skies and light
  winds, a surface inversion can form as the sun
  sets.
• Surface inversion will continue into the morning
  until the sun begins to heat the ground.

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Precautions for Inversions

• Surface inversions are common .
• Be especially careful near sunset and an hour or
  so after sunrise, unless
• There is low heavy cloud cover
• The wind speed is greater than 5-6 mph at ground
  level
• 5 degree temp rise after sun-up
• Use of a smoke bomb or smoke
• generator is recommended to
• identify inversion conditions.

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Spray Droplet Size
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Efficacy and Drift Potential is Influenced by

• Size of the Spray Droplets -
• Volume Median Diameter (VMD)
• Droplet Spectrum (Range - big to small)

Volume in droplets less than 200 microns in
size
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Relationship of Drift to Drop Size
One micron (?m) 1/25,000 inch
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Comparison of Micron Sizes for Various Items
(approximate values)

• pencil lead 2000 (?m)
• paper clip 850 (?m)
• staple 420 (?m)
• toothbrush bristle 300 (?m)
• sewing thread 150 (?m)
• human hair 100 (?m)

150
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Spray Droplet Movement with Various Wind Speeds
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1/2 of spray volume smaller droplets
VMD
1/2 of spray volume larger droplets
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Evaporation of Droplets
High Relative Humidity Low Temperature
Low Relative Humidity High Temperature
Fall Distance
Wind
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Spray Characteristics are Important to Understand
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
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XR Flat-fan _at_20, 40, 80 PSI
Turbodrop XL _at_20, 40, 80 PSI
Boom
Drift
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ASAE DSC and Volume Median Diameter (DV0.5) From
PMS Laser Spectrometer
Droplet Spectra Classification (DSC)
Droplet Size Range

• Very Fine (VF) lt 182µm
• Fine (F) 183-280µm
• Medium (M) 281-429µm
• Coarse (C) 430-531µm
• Very Coarse (VC) 532-655µm
• Extremely Coarse (XC) gt656µm

USDA ARS College Station, TX
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Strategies to Reduce Drift

• Select nozzle to increase drop size
• Increase flow rates - higher application volumes
• Use lower pressures
• Use lower spray (boom) heights
• Avoid adverse weather conditions
• Consider using buffer zones
• Consider using new technologies
• drift reduction nozzles
• drift reduction additives
• shields, electrostatics, air-assist

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Some Other Things to Keep in Mind when Planning a
Spray Application

• Allow enough time for
• Scheduling and planning the application
• Obtaining the products
• Setting up the application date
• Weather delays or maintenance problems, if
  necessary.

Try not to fall into the trap of declaring I
need to spray RIGHT NOW!. Forcing a job under
poor conditions almost always leads to drift or
other errors.
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In Conclusion
Minimizing spray drift is in the best interests
of everyone. Do your part to keep agrichemical
applications on target.
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Thank You