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Understanding Spray Drift. Why Interest in Drift?. Spotty pest control Wasted chemicals Off-target damage More high value specialty crops Less tolerant neighbors Litigious Society Result-higher costs-$$$ More wind?? (Timing) Environmental impact Water and Air Quality

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Presentation Transcript
why interest in drift
Why Interest in Drift?
  • Spotty pest control
  • Wasted chemicals
  • Off-target damage
  • More high value specialty crops
  • Less tolerant neighbors
  • Litigious Society
  • Result-higher costs-$$$
  • More wind?? (Timing)
  • Environmental impact
    • Water and Air Quality
  • Public more aware of pesticides

(Negative) (Perceptions)

  • Urban sprawl
the drift
The Drift:
  • Creating smaller spray drops will result in increased drift.
nozzles are important
Nozzles are important:
  • Control the amount – GPA.
  • Determine uniformity of application.
  • Affects the coverage.
  • Influences the drift potential.
definition of drift
Definition of Drift:

Movement of spray particlesand vaporsoff-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people.

types of drift
Types of Drift:

Vapor Drift - associated with volatilization (gas, fumes)

Particle Drift - movement of spray particles during or after the spray application

factors affecting drift
Factors Affecting Drift:
  • Equipment & Application
    • nozzle type
    • nozzle size
    • nozzle pressure
    • height of release
  • Weather
    • air movement (direction and velocity)
    • temperature and humidity
    • air stability/inversions
    • topography

Spray Characteristics

  • chemical
  • formulation
  • drop size
  • evaporation
wind direction
Wind Direction:
  • Wind direction is very important
    • Know the location of sensitive areas - consider safe buffer zones.
    • Do not spray at any wind speed if it is blowing towards sensitive areas
    • Spray when breeze is gentle, steady, and blowing away from sensitive areas.
    • “Dead calm” conditions arenever recommended.
more drift at low wind speeds
More drift at low Wind speeds?
  • Because:
    • Light winds (0-3 mph)

- unpredictable & variable in ALL directions.

    • 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.
wind current effects
Wind Current Effects

Structures drastically affect wind currents

  • Wind breaks
  • Tree lines and orchards
  • Houses and barns
  • Hills and valleys
wind patterns near treelines
Wind Patterns Near Treelines

Adapted from Survey of Climatology:

Griffiths and Driscoll,

Texas A&M University, 1982






Floating Ball


Wind Wizard



Turbo Meter

Wind speed - knots, feet/min, meters/sec, mph


Kestrel 1000

Maximum, average, current wind speed

- knots, feet/min, meters/sec, mph


Kestrel 2000

Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec, mph


Kestrel 3000

All wind speed features plus temp, wind chill, dew point, heat index, relative humidity


Plastimo Iris 50**



Wind Meters and Compass

*Prices for Wind Meters taken from Gempler’s 2000 Master Catalog

**Plastimo Airguide Inc., 1110 Lake Cook Road, Buffalo Grove, IL 60089(708-215-7888)

inversions normal conditions

Normal Temperature Profile


Temperature decreases

with height



Increasing Temperature

Inversions: Normal Conditions

Air tends to rise and mix with the air above.

Droplets will disperse and will usually not cause problems.

temperature inversions

Temperature Inversion

Warm Air

Temperature increases

with height


Cool Air

Increasing Temperature

Temperature Inversions:

Temperature increases as you move upward.

Prevents air from mixing with the air above it.

Small suspended droplets form a concentrated cloud

Move in unpredictable directions.

relationship of drift to drop size
Relationship of Drift to Drop Size

One micron (m) =1/25,000 inch

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)

Comparison of Micron Sizes for Various Items: (approximate values)



Droplet Class

Droplet Size


  • Very Fine (VF) < 182µm
  • Fine (F) 183-280µm
  • Medium (M) 281-429µm
  • Coarse (C) 430-531µm
  • Very Coarse (VC) 532-655µm
  • Extremely Coarse (XC) >656µm

*USDA ARS College Station, TX

efficacy and drift potential is influenced by
Efficacy and Drift Potential is Influenced by:
  • Size of the Spray Droplets -

Volume Median Diameter (VMD)

  • Droplet Spectrum (Range - big to small)

1/2 of spray volume = smaller droplets


1/2 of spray volume = larger droplets

evaporation of droplets
Evaporation of Droplets

High Relative Humidity

Low Temperature

Low Relative Humidity

High Temperature

Fall Distance


nozzle technology
Nozzle Technology?
  • Nozzles designed to reduce drift
  • Improved drop size control
  • Emphasis on ‘Spray Quality’
spray characteristics are important to understand
Spray Characteristics are Important to Understand:

Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind

strategies to reduce drift
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
some other things to keep in mind when planning a spray application
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.