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

2. Why Interest in Drift? Spotty pest control Wasted chemicals
Off-target damage
More high value specialty crops
Urban sprawl and.....
Less tolerant neighbors
Litigious Society
More wind?? (Timing)
Environmental impact
Water and Air Quality
Public more aware of pesticide
concerns! (Negative) (Perceptions)
Result-higher costs-$$$

3. Productivity
The application
triangle
Off-site protection
Efficacy

4. Status of EPA Label Guidance Proposal on Drift

5. Spray Drift Task Force April 1990 38 Companies $20 Million 21 Studies
Airblast, Aerial,
Ground, Chemigation
40 Reports
Downwind!!!!
Droplet size!!!!

6. SDTF Purpose
To develop spray drift data required to fulfill data call-in requirements from the USEPA.
Help formulate label language regarding application methods to reduce spray drift.
Provide educational opportunities to develop best management practices which reduce spray drift.
Formed National Coalition on Drift Minimization (NCODM) in 1995
Straight Talk About Minimizing Spray Drift - A Guide for Applicators

7. Drift Labeling Guidance Issues
EPA’s Proposal and Follow-up
Draft Guidance for labeling statements for controlling spray and dust drift was published in the Federal Register (2001) and public comments have been received.
The draft guidelines elicited extensive comments to EPA from most all segments of the industry. EPA is in process of reviewing and considering everything that was received. They plan to have some listening sessions around the country and to issue a revised guideline proposal that will be open for public comment.

8. Major objections: (5000+ comments)
Against ‘zero tolerance’
‘10 MPH’ wind limit
‘4-foot’ ground boom height limit
’10-foot’ aerial boom height limit
Need more restrictions!!!!!

9. Proposed Implementation
When????
Proposed Implementation
After considering all comments and further public listening sessions, EPA plans to issue a revised proposal for comments.
Issue final guidance to registrants
200????
EPA is reviewing the comments received from the August 2001 issue of the draft label language guidance. They plan to have listening sessions around the country before they finalize a revision of label language guidance. They plan to receive comments on the revision and then issue the final guidance.

10. So What’s Happening Now??
In the mean time, registrants can:
Go with the current draft labeling.
Propose something else that’s at least as protective that EPA will accept.
Go with previous labeling guidelines.
Go with old standard – ‘do not allow drift’.
Trial statements!!!!

11. EPA’s Bottom-line Message
EPA and Drift!
EPA’s Bottom-line Message
Concerns about spray drift and its adverse effects are taken seriously.
Improvements in education/behavior, technology, and labeling are key issues
Flexibility and openness to achieve goals

12. For more information contact

13. Technical Aspects of Spray Drift

14. 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

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

16. 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

17. 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.

18. 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.

19. Spray Droplet Movement with Various Wind Speeds
The information presented on this slide demonstrates the effects of wind on the spray droplets. Note that the distances the droplets move are dramatically higher with the smaller droplets. As the droplet sizes increase, the distances moved decreases.
Thus, larger spray droplets have a far greater opportunity to deposit on the target area.

20. 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.

21. 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.

22. Wind Patterns Near Shelterbelts 3 2
Height
Wind Patterns Near Shelterbelts
This diagram shows the effects of a shelterbelt or tree line on the wind and the resulting currents developed.
Note that on the upwind side of the trees the winds are flowing along in a laminar manner. As the currents approach the trees, the atmospheric pressure rises and the deflection of the wind currents begins. While most of the wind currents are deflected over the top of the trees, some of the currents are trapped in the trees.
On the downwind side, there is a turbulent area and a relatively calm area.
This describes how spray droplets are often moved by wind currents to unexpected areas-i.e., symtomology may be observed at the tops of trees as well as areas near the ground.
Distance from shelterbelt (tree heights)
Generalized pattern of wind in the neighborhood of a shelterbelt.

23. 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

24. 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)

25. Wind Patterns Around Buildings
Overhead
View
Wind
This overhead sketch of the wind currents around a building show how the swirling currents would allow the deposition of drifting fine droplets.
Diagram of Wind Around a Building
Adapted From Farm Structures*
* H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)

26. 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 2002 Master Catalog
**Plastimo Airguide Inc., 1110 Lake Cook Road, Buffalo Grove, IL 60089( )

27. 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.

28. 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.

29. 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.

30. Courtesy – George Ramsay, Dupont

31. 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.

32. Spray Droplet Size

33. 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

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

35. 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

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

37. 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

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

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

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

41. ASAE S-572 Droplet Size Standard

42. Coverage Need knowledge of the product being used. What is the target?
Systemic
Contact
What is the target?
Soil
Grass
Broadleaf (smooth, hairy, waxy)
Leaf orientation – time of day

43. 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

45. Computer Models:

46. AgDRIFT® Program Map

47. Example of Model Use – Aerial Applicators Standard Operation

48. 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 high application speeds/rapid speed changes
Avoid adverse weather conditions
High winds, light & variable winds, calm air
Consider using buffer zones
Consider using new technologies:
drift reduction nozzles
drift reduction additives
shields, electrostatics, air-assist

49. Drift Reduction Additives:
Many available!
Not EPA regulated
Long chain polymers
New-soluble powders
% reduction in off-target movement
Pump shear problems
Effect on the pattern?

50. Goodland Drift Project
8 Companies
19 Drift Reduction/Deposition Aids
Water
.25%
2 Airplanes
AT Hawkeye – Bill and Dave
Cessna Ag Husky w/wing tips – Cary
3 reps with the drift tower
1 pass over a canopy – top and bottom
260 flight passes each
4600 cards

51. Participants in the Study:
Companies
Products
41-A
Formula One
AMS 20/10
Border EG 250
Control
INT VWZ
Inplace
Garco Exp-3
INT YAR
Border XTRA 8L
HM2005-C
HM0226
Liberate
Target LC
HM2052
INT HLA
HM 0230
Valid
Double Down
United Suppliers
Helena Chemical
Garco
Loveland
Wilber-Ellis
Rosen’s
Precison Labs
SanAg

52. 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.

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

54. Thank You

55. For more information contact: