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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
Technical Aspects of Spray Drift
The Drift:
Creating smaller spray drops will result in increased drift.
Technical Aspects of Spray Drift
Nozzles are important:
Control the amount – GPA. Determine uniformity of application. Affects the coverage. Influences the drift potential.
Technical Aspects of Spray Drift
Definition of Drift:
Movement of spray particles and vapors off-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people.
Technical Aspects of Spray Drift
Types of Drift:
Vapor Drift - associated with volatilization (gas, fumes)
Particle Drift - movement of spray particles during or after the spray application
Technical Aspects of Spray Drift
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
Technical Aspects of Spray Drift
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.
Technical Aspects of Spray Drift
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?
Technical Aspects of Spray Drift
Wind Current Effects
Structures drastically affect wind currentsWind breaksTree lines and orchardsHouses and barnsHills and valleys
Technical Aspects of Spray Drift
Wind Patterns Near Treelines
Adapted from Survey of Climatology:Griffiths and Driscoll,
Texas A&M University, 1982
Technical Aspects of Spray Drift
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)
Technical Aspects of Spray Drift
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
Technical Aspects of Spray Drift
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:
Technical Aspects of Spray Drift
Recognizing Inversions:
Spray Droplet Size
Technical Aspects of Spray Drift
One micron (m) =1/25,000 inchOne micron (m) =1/25,000 inch
Relationship of Drift to Drop SizeRelationship of Drift to Drop Size
Technical Aspects of Spray Drift
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
Technical Aspects of Spray Drift
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
Technical Aspects of Spray Drift
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)
Technical Aspects of Spray Drift
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
Technical Aspects of Spray Drift
Evaporation of Droplets
Wind
High Relative HumidityLow Temperature
Low Relative HumidityHigh Temperature
Fal
l Dis
tanc
e
Technical Aspects of Spray Drift
Nozzle Technology? Nozzles designed to reduce drift Improved drop size control Emphasis on ‘Spray Quality’
Technical Aspects of Spray Drift
Spray Characteristics are Important to Understand:
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
Technical Aspects of Spray 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
Technical Aspects of Spray Drift
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.
Technical Aspects of Spray Drift