1. Understanding Spray Drift
Robert E. Wolf
Extension Specialist
Biological and Agricultural Engineering

2. Why Interest in Drift? Water and Air Quality 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

3. Nozzle Technology? Nozzles designed to reduce drift
Improved drop size control
Emphasis on ‘Spray Quality’
Beginning with the ‘extended range’ flat fan nozzle (all major manufactures have one), continuing with the design of ‘preorifice inserts’ and ‘turbulation chambers’, and now with the ‘venturi’ style nozzle design, nozzle manufacturer's have worked to develop nozzles that are improving the quality of spray emitted.

4. Nozzles are important:
Control the amount – GPA.
Determine uniformity of application.
Affects the coverage.
Influences the drift potential.

5. 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?

6. Technical Aspects of Spray Drift

7. 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

8. Types of Drift:
Vapor Drift - associated with volatilization (gas, fumes)
Particle Drift - movement of spray particles during or after the spray application

9. 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 5

10. 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.

11. However, Drift Potential May be High at Low Wind Speeds
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.

12. Wind Speeds Gradients Wind Speed Height Above Crop Canopy, Feet30 20 10 6 2
11 mph
10 mph
8 mph
7 mph
5 mph
Height Above Crop Canopy, Feet
Wind Speed
This diagram shows that as the height above the ground or the crop increases the velocity of the wind increases.
This is a natural phenomenon.
The relation between height above the canopy of a crop like cotton or soybean and the speed of wind.

13. 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
Wind and air currents can drastically affect spray droplet deposition.
When the wind blows against structures, the direction of the wind currents can be drastically affected. In this discussion, structures will be used to define anything that can deflect wind flow.

14. Wind Patterns Near Treelines
This diagram of wind currents has several applications.
If there was a field between two tree lines then the turbulent and circular flows described could result in spray droplet deposition even in upwind areas bordering the field
If the sketch was depicting level fields with a ditch or depression, then one could understand how product was moved down into the depression by wind currents.
Areas with topographical variability-i.e, a combination of hills, valleys, woodlands-can present even greater variables which result in spray droplet deposition in areas that would be difficult to explain without these diagrams.
Adapted from Survey of Climatology:
Griffiths and Driscoll,
Texas A&M University, 1982

15. Wind Patterns Around Buildings
Ground
This diagram and the following one describe the flow of winds around a building or similar structure. Notice how the air swirls toward the ground on the downwind side of the building. Drifting fine droplets could easily be deposited here.
Diagram of wind around a building.
Adapted from Farm Structures*
* H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)

16. Wind Meters and Compass
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
*Prices for Wind Meters taken from Gempler’s 2000 Master Catalog
**Plastimo Airguide Inc., 1110 Lake Cook Road, Buffalo Grove, IL 60089( )

17. Inversions:
Normal Temperature Profile
Altitude
Cooler
Warmer
Temperature decreases
with height
Increasing Temperature
Under normal conditions air tends to rise and mix with the air above. Droplets will disperse and will usually not cause problems.

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

19. 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.

20. Courtesy – George Ramsay, Dupont

21. 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.

22. Spray Droplet Size

23. Efficacy and Drift Potential is Influenced by:
Size of the Spray Droplets -
Volume Median Diameter (VMD)
Droplet Spectrum (Range - big to small)
% Volume in droplets less than
200 microns in size

24. Relationship of Drift to Drop Size
One micron (m) =1/25,000 inch

25. Comparison of Micron Sizes for Various Items: (approximate values)
pencil lead (m)
paper clip (m)
staple (m)
toothbrush bristle (m)
sewing thread (m)
human hair (m)
150 9

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

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

28. Important Droplet Statistics:
VMD
(50%)
Operational Area
VD0.9
(90%)
VD0.1
(10%)

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

30. Spray Characteristics are Important to Understand:
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind

31. XR 40, 80 PSI
Turbodrop 40, 80 PSI
Boom
Drift

32. EPA Requested Changes Coming!!!!
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
Example Reference Graph
Cumulative Volume Fraction
0.1
0.5
0.9
Drop Size (microns)
100
200
300
400
500
600
700
800
900
very fine/ fine
fine/medium
medium/ coarse
coarse/ very coarse
very coarse/ extremely coarse VF F M C VC XC
VMD

33. Origin Of Standardized Spray Droplet Size Categories
British Crop Protection Council (BCPC)
Droplet size classifications, primarily designed to enhance efficacy.
Uses the term SPRAY QUALITY for droplet size categories.
ASAE Standard S572
Droplet size classifications, primarily designed to control spray drift.
Uses the term DROPLET SPECTRA CLASSIFICATION for droplet size categories.

34. ASAE DSC and Volume Median Diameter (DV0. 5) From PMS
ASAE DSC and Volume Median Diameter (DV0.5) From PMS* Laser Spectrometer
Droplet Spectra
Classification (DSC)
Droplet Size
Range
Very Fine (VF) < 182µm
Fine (F) µm
Medium (M) µm
Coarse (C) µm
Very Coarse (VC) µm
Extremely Coarse (XC) >656µm
These size categories are developed from an ASAE standard reference nozzle set with a laser instrument. Spray nozzles and their operational parameters must then be characterized by the same laser instrument. The DSC categories from VF to XC are from the ASAE standard, the size ranges were obtained with the USDA ARS PMS system at College Station, Texas. Other instruments may give slightly different droplet size ranges with the respective DSC, but it is expected that a different laser system would give the same DSC for the same spray spectrum when the reference nozzles have been used to develop the droplet size ranges for each DSC with that different laser system and that system is in turn used to classify the DSC of the given spray spectrum. The standard requires that the same system be used for classifying nozzles that is used for establishing the size categories with the ASAE standard reference nozzle set.
*USDA ARS College Station, TX

36. 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

37. In Conclusion:
Minimizing spray drift is in the best interests of everyone. Do your part to keep agrichemical applications on target.

38. Thank You