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Understanding Spray Drift
Robert E. Wolf Extension Specialist
Biological and Agricultural Engineering
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
Nozzle Technology? Nozzles designed to reduce drift Improved drop size control Emphasis on ‘Spray Quality’
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
Will affect drift:
Movement of spray particles off-target.
Creating smaller spray drops will result in increased drift.
Is it Coverage vs Drift? What is the answer?
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
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) tend to be unpredictable and variable in direction. Calm and low wind conditions may
indicate presence of a temperature inversion.
Drift potential is lowest at wind speeds between 3 and 10 mph (gentle but steady breeze) blowing in a safe direction.
However, Drift Potential May be High at Low Wind Speeds
Technical Aspects of Spray Drift
Wind Speeds Gradients
The relation between height above the canopy of a crop like cotton or soybean and the speed of
wind.
30
20
10
6
2
0
11 mph
10 mph
8 mph
7 mph
5 mph
Hei
gh
t A
bo
ve C
rop
Can
op
y, F
eet
Wind Speed
Technical Aspects of Spray Drift
Wind Current Effects
Wind currents can drastically affect spray droplet deposition
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
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)
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
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:
Technical Aspects of Spray Drift
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:
Technical Aspects of Spray Drift
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.
Technical Aspects of Spray Drift
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
Courtesy – George Ramsay, Dupont
Technical Aspects of Spray Drift
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.
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)
% Volume in droplets less than 200 microns in size
% Volume in droplets less than 200 microns in 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
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
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
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
Spray Characteristics are Important to Understand:
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
Technical Aspects of Spray Drift
XR Flat-fan @20, 40, 80 PSI Turbodrop XL @20, 40, 80 PSI
Boom
Drift
Technical Aspects of Spray Drift
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!!!!
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
Technical Aspects of Spray Drift
Origin Of Standardized Spray Droplet Size Categories
1985 -- British Crop Protection Council (BCPC) Droplet size classifications, primarily
designed to enhance efficacy. Uses the term SPRAY QUALITY for droplet
size categories.2000 -- ASAE Standard S572 Droplet size classifications, primarily
designed to control spray drift. Uses the term DROPLET SPECTRA
CLASSIFICATION for droplet size categories.
Technical Aspects of Spray Drift
ASAE DSC and Volume Median Diameter (DV0.5) From PMS* Laser Spectrometer
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 Spectra Classification (DSC)
Droplet SizeRange
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
In Conclusion:
Minimizing spray drift is in the Minimizing spray drift is in the best interests of everyone. Do best interests of everyone. Do your part to keep agrichemical your part to keep agrichemical
applications on target.applications on target.