Understanding Spray Drift Technical Aspects of Spray Drift Why Interest in Drift? u Spotty pest control u Wasted chemicals u Off-target damage u More

Understanding Spray Drift

Technical Aspects of 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 Public more aware of pesticides

(Negative) (Perceptions) Urban sprawl


The Drift:

Creating smaller spray drops will result in increased drift.


Nozzles are important:

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


Definition of Drift:

Movement of spray particles and vapors off-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people.


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:Spray Characteristics

chemical formulation drop size evaporation

Equipment & Application nozzle type nozzle size nozzle pressure height of releaseWeather

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


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

ALL NOZZLES CAN DRIFT. Spray when breeze is gentle, steady, and

blowing away from sensitive areas. “Dead calm” conditions are never

recommended.


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.

More drift at low Wind speeds?


Wind Current Effects

Structures drastically affect wind currentsWind breaksTree lines and orchardsHouses and barnsHills and valleys


Wind Patterns Near Treelines

Adapted from Survey of Climatology:Griffiths and Driscoll,

Texas A&M University, 1982


Name Features Cost*

Dwyer Floating Ball 15.50

Wind Wizard Mechanical 39.50

Turbo Meter Wind speed - knots, feet/min, meters/sec, mph 135.00

Kestrel 1000 Maximum, average, current wind speed- knots, feet/min, meters/sec, mph

89.00

Kestrel 2000 Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec,

mph

119.00

Kestrel 3000 All wind speed features plus temp, wind chill, dew point, heat index, relative humidity

159.00

Plastimo Iris 50** Compass 89.00

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)


Air tends to rise and mix with the air above.

Droplets will disperse and will usually not cause problems.

Normal Temperature Profile

Altitude

Cooler

Warmer

Temperature decreases with height

Increasing Temperature

Inversions: Normal Conditions


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.

Temperature Inversion

Altitude

Temperature increases with height

Warm Air

Cool Air

Increasing Temperature

Temperature Inversions:


Recognizing Inversions:

Spray Droplet Size


One micron (m) =1/25,000 inchOne micron (m) =1/25,000 inch

Relationship of Drift to Drop SizeRelationship of Drift to Drop Size


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


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

Droplet Class Droplet SizeRange


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)

Size of the Spray Droplets -

Volume Median Diameter (VMD) Droplet Spectrum (Range - big to small)


1/2 of spray volume = larger droplets1/2 of spray volume = larger droplets

VMDVMD

1/2 of spray volume = smaller droplets1/2 of spray volume = smaller droplets


Evaporation of Droplets

Wind

High Relative HumidityLow Temperature

Low Relative HumidityHigh Temperature

Fal

l Dis

tanc

e


Nozzle Technology? Nozzles designed to reduce drift Improved drop size control Emphasis on ‘Spray Quality’


Spray Characteristics are Important to Understand:

Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind


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

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.


Documents

Understanding Spray Drift Technical Aspects of Spray Drift Why Interest in Drift? u Spotty pest control u Wasted chemicals u Off-target damage u More