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Technical Aspects of Spray Drift
Technical Technical Aspects of Aspects of Spray DriftSpray Drift
Reeves PetroffMontana State University
Extension Pesticide EDUCATION Specialist
Technical Aspects of Spray Drift
Why Interest in Drift?Why Interest in Drift? Spotty pest control Wasted chemicals Off-target damage Litigious Society Result-higher costs-$$$ More wind?? (Timing) Environmental impact
Water and Air Quality Public more aware of pesticide
concerns! (Negative)
Spraying in more populated areas? (Suburbs)
Technical Aspects of Spray Drift
Big lies
The check is in the mail. I love you. There’s no wind on the drop zone. Always use the biggest drop possible. Its best to spray when there’s no wind Increase pressure to increase GPA
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.
Large droplets maybe result in bounce.
$64,000 Question?
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
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
chemicalformulationdrop sizeevaporation
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..
Do not spray at any wind speed if it is blowing towards sensitive areas…
Spray when breeze is gentle, steady, and blowing AWAY from sensitive areas.
“Dead calm” conditions are recommended.
safe buffer zones.
---all nozzles can drift---
NEVER
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
Spray Droplet Size
Technical Aspects of Spray Drift
Drift is Influenced by:Drift 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
Nozzle Drop Size ClassesNozzle Drop Size Classes
Very Fine to Fine < 200 um
Medium to Coarse – 200 to 450 um
Very Coarse > 450 um
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
Important Droplet Statistics:
Operational Area
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
Cutting Droplet Size in Half
Cutting Droplet Size in Half
Results in Eight Times the Number of
Droplets
Results in Eight Times the Number of
Droplets
==2 more droplets fill in
the sphere2 more droplets fill in
the sphere
500Microns
500Microns 250
Microns
Technical Aspects of Spray Drift
Spray Droplet Movement with Various Wind SpeedsDropletSizes(microns)
5 mphWind
10 mphWind
15 mphWind
20mphWind
100 24 ft. 48 ft. 72 ft. 96 ft.
200 9 18 26 35
400 5 9 14 18
500 4 7 10 14
600 3 6 9 12
Boom height: 3 feet
Technical Aspects of Spray Drift
Wind Speeds Gradients
The relation between height above the canopy of a crop 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 currents Wind breaks Tree lines and orchards Houses and barns Hills and valleys
Technical Aspects of Spray Drift
Wind Patterns Near Shelterbelts
Distance from shelterbelt (tree heights)
Generalized pattern of wind in the neighborhood of a shelterbelt.
5 0 5 10 15
Hei
gh
t
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
Wind Patterns Around Buildings
Diagram of Wind Around a BuildingAdapted From Farm Structures*
OverheadView
WindWind
* 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 rises and mixes 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
Temperature increases with altitude. 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
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
Notice smoke or dust patterns to
identify inversion conditions.
Technical Aspects of Spray Drift
Evaporation and Deceleration of Various Size Droplets*Droplet
Diameter(microns)
TerminalVelocity(ft/sec)
Final Dropdia.
(microns)
Time toevaporate
(sec)
Decelerationdistance
(in)
20 .04 7 0.3 <1
50 .25 17 1.8 3
100 .91 33 7 9
150 1.7 50 16 16
200 2.4 67 29 25
*Conditions assumed: 90 F, 36% R.H., 25 psi., 3.75% pesticide solution
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
Tip Spray Selection by Drop Size
Turbo TeeJet Flat-fan
Technical Aspects of Spray Drift
XR Flat-fan @ 20, 40, & 80 psi Turbodrop XL @ 20, 40, & 80 psi
Technical Aspects of Spray Drift
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
In Conclusion:
Minimizing spray drift is in Minimizing spray drift is in the best interests of the best interests of
everyone. Do your part to everyone. Do your part to keep pesticides on target.keep pesticides on target.
Minimizing spray drift is in Minimizing spray drift is in the best interests of the best interests of
everyone. Do your part to everyone. Do your part to keep pesticides on target.keep pesticides on target.
Technical Aspects of Spray Drift
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