Understanding Spray Drift Robert E. Wolf Extension Specialist Application Technology

Why Interest in Drift? ü Spotty pest control ü Wasted chemicals ü Off-target damage ü Litigious Society ???? ü Result - higher costs - $$$ ü Windy?? (Timing) ü Environmental impact (Water and Air Quality) ü Spotty pest control ü Wasted chemicals ü Off-target damage ü Litigious Society ???? ü Result - higher costs - $$$ ü Windy?? (Timing) ü Environmental impact (Water and Air Quality)

Misapplication Facts:

Facts about drift:

Why is the Nozzle Important? ü Amount of spray applied ü Uniformity of the spray ü Coverage on the target ü Amount of off-target drift

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. Adapted from National Coalition on Drift Minimization 1997 as adopted from the AAPCO Pesticide Drift Enforcement Policy - March 1991

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

Wind Direction: ü 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.

NameFeaturesCost* DwyerFloating Ball15.50 Wind WizardMechanical39.50 Turbo MeterWind speed - knots, feet/min, meters/sec, mph Kestrel 1000Maximum, average, current wind speed - knots, feet/min, meters/sec, mph Kestrel 2000Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec, mph Kestrel 3000All wind speed features plus temp, wind chill, dew point, heat index, relative humidity Plastimo Iris 50**Compass89.00 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( )

Under normal conditions 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:

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. Temperature Inversion Altitude Temperature increases with height Warm Air Cool Air Increasing Temperature Temperature Inversions:

Recognizing Inversions: ü Under clear to partly cloudy skies and light winds, a surface inversion can form as the sun sets. ü Under these conditions, a surface inversion will continue into the morning until the sun begins to heat the ground.

Precautions for Inversions: ü Surface inversions are common. ü 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 ü Use of a smoke bomb or smoke generator is recommended to identify inversion conditions.

Wind Patterns Near Treelines: Adapted from Survey of Climatology: Griffiths and Driscoll, Texas A&M University, 1982

Wind Patterns Around Buildings Diagram of wind around a building. Adapted from Farm Structures* Ground * H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)

Spray Droplet Size

ü Particle drift will result from the smaller drops created during the spray process. The size of the droplets created is critical. ü Dropsizes are measured in microns using laser beams. Drift & Dropsize Relationship:

Dropsize Facts: ü One micron = 1/25,000 inch ü Expressed as (VMD) Volume Median Diameter ü Example - VMD = 500 microns

Comparison of Micron Sizes for Various Items: (approximate values) ü pencil lead 2000 (  m ) ü paper clip 850 (  m ) ü staple 420 (  m ) ü toothbrush bristle 300 (  m ) ü sewing thread150 (  m ) ü human hair100 (  m ) 150

Raindrop compared to a Turbo Turf Flood Raindrop DropTurbo Turf Flood 5.0 MPH wind at 40 psi

1/2 of spray volume = larger droplets VMD 1/2 of spray volume = smaller droplets

Cutting Droplet Size in Half Results in Eight Times the Number of Droplets 500 Microns 500 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns

Important Droplet Statistics: Operational Area

Evaporation of Droplets Wind High Relative Humidity Low Temperature Low Relative Humidity High Temperature Fall Distance

Strategies to Reduce Drift: ü Select nozzle to increase drop size ü Increase flow rates - higher application volumes ü Use lower pressures ü Use lower spray (boom) heights ü Avoid adverse weather conditions ü Consider using buffer zones ü Consider using new technologies: drift reduction nozzles drift reduction additives shields

Drift Reduction Additives: ü Many available! ü Not EPA regulated ü Long chain polymers ü New-soluble powders ü % reduction in off-target movement ü Pump shear problems

Example Reference Graph Cumulative Volume Fraction Drop Size (microns) very fine/ fine fine/medium medium/ coarse coarse/ very coarse very coarse/ extremely coarse VF F M C VC XC ü New Label language- EPA Reviewing Public Comments ü Public ‘Listening Sessions’ planned ü Sometime in 2003?? ü Match the crop protection product to the target ü Adhere to label guidelines based on an industry standard ASAE S-572 ü Buffer Zones or No Spray Zones ü Maximize Efficacy ü Minimize Drift EPA Requested Changes Coming!!!!

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