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Understanding Spray Understanding Spray DriftDrift
Robert E. WolfExtension Specialist
Application Technology
Why Interest in Drift?Why Interest in Drift?
Spotty pest control Wasted chemicals Off-target damage Litigious Society ???? Result - higher costs - $$$ Windy?? (Timing) Environmental impact (Water and Air Quality)
Spotty pest control Wasted chemicals Off-target damage Litigious Society ???? Result - higher costs - $$$ Windy?? (Timing) Environmental impact (Water and Air Quality)
Misapplication Facts:
2%8%
24%
33%
33%
Equipment
Drift
Tank Mix
Wrong Field
Off Label
Facts about drift:
13%
26%
38%
23%
Nozzle
Applicator
Physical
Other
Why is the Nozzle Important?
Amount of spray appliedUniformity of the sprayCoverage on the targetAmount of off-target drift
Technical Aspects of Spray 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
releaseWeather
air movement (direction and velocity)
temperature and humidity air stability/inversions topography
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 - all nozzles can drift.
• Spray when breeze is gentle, steady, and blowing away from sensitive areas.
• “Dead calm” conditions are never recommended.
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)
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:Inversions:
Under these conditionsthe 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:Temperature Inversions:
Recognizing Inversions:Recognizing Inversions:
Under clear to partly cloudy skies and light winds, a surface inversion can form as the sun sets.
Under these conditions, a surface inversion will continue into the morning until the sun begins to heat the ground.
Cloud of 5-25 u oil droplets generated under unstable conditions
105 foot temperature monitoring tower
8’ 41°F
16’ 41°F
32’ 40°F
64’ 40°F
105’ 38°F
8’ 33°F16’ 36°F32’ 37°F64’ 38°F
105’ 38°F
.5 mph wind
2.5 mph wind
Shallow surface inversionSTABLE conditions up to 64’ NEUTRAL conditions at 105’
Cloud is dispersing
Precautions for Inversions: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.
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 SizeSpray Droplet Size
Particle drift will result from the smaller drops created during the spray process. The size of the droplets created is critical.
Dropsizes are measured in microns using laser beams.
Drift & Dropsize Relationship:
Dropsize Facts:
One micron = 1/25,000 inchExpressed as (VMD) Volume Median DiameterExample - VMD = 500 microns
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
Raindrop compared to a Turbo Turf FloodRaindrop compared to a Turbo Turf Flood
Raindrop DropTurbo Turf Flood
5.0 MPH wind at 40 psi
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
Cutting Droplet Size in HalfResults in Eight Times the Number of Droplets
Cutting Droplet Size in HalfResults in Eight Times the Number of Droplets
500Microns
500Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
250Microns
Important Droplet Statistics:Important Droplet Statistics:
Operational Area
Evaporation of DropletsEvaporation of Droplets
Wind
High Relative HumidityLow Temperature
Low Relative HumidityHigh Temperature
Fal
l Dis
tanc
e
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
Drift Reduction Additives:Drift Reduction Additives:
Many available! Not EPA regulated Long chain polymers New-soluble powders 50 - 80% reduction in
off-target movement Pump shear problems
Example Reference Graph
Cumulative Volume Fraction
0.1 0.5 0.9
Drop S
ize (microns) 0
100
200
300
400
500
600
700
800
900
very fine/ fine fine/mediummedium/ coarsecoarse/ very coarsevery coarse/ extremely coarse
VF
F
M
CVC
XC
New Label language-EPA Reviewing Public Comments
Public ‘Listening Sessions’ planned
Sometime in 2003?? Match the crop
protection product to the target
Adhere to label guidelines based on an industry standard • ASAE S-572
Buffer Zones or No Spray Zones
Maximize Efficacy Minimize Drift
EPA Requested Changes Coming!!!!EPA Requested Changes Coming!!!!
Example Reference Graph
Cumulative Volume Fraction
0.1 0.5 0.9
Dro
p S
ize
(mic
rons
)
0
100
200
300
400
500
600
700
800
900
very fine/ fine fine/mediummedium/ coarsecoarse/ very coarsevery coarse/ extremely coarse
VF
F
M
CVC
XC
For more information contact:For more information contact:
www.bae.ksu.edu/rewolf/