Understanding Spray Drift

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

2. 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

3. Nozzle Technology? • Nozzles designed to reduce drift • Improved drop size control • Emphasis on ‘Spray Quality’

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 particlesand vaporsoff-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: • Equipment & Application • nozzle type • nozzle size • nozzle pressure • height of release • Weather • air movement (direction and velocity) • temperature and humidity • air stability/inversions • topography Spray Characteristics • chemical • formulation • drop size • evaporation

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 arenever 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. 30 20 10 6 2 0 11 mph 10 mph 8 mph Height Above Crop Canopy, Feet 7 mph 5 mph Wind Speeds Gradients Wind Speed 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

14. Wind Patterns Near Treelines Adapted from Survey of Climatology: Griffiths and Driscoll, Texas A&M University, 1982

15. Wind Patterns Around Buildings Ground Diagram of wind around a building. Adapted from Farm Structures* * H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)

16. 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)

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

18. Temperature Inversion Warm Air Temperature increases with height Altitude Cool Air Increasing Temperature Temperature Inversions: 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. pencil lead 2000 (m) paper clip 850 (m) staple 420 (m) toothbrush bristle 300 (m) sewing thread 150 (m) human hair 100 (m) Comparison of Micron Sizes for Various Items: (approximate values) 150

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

27. Cutting Droplet Size in HalfResults 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 Flat-fan @20, 40, 80 PSI Turbodrop XL @20, 40, 80 PSI Boom Drift

32. 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 900 800 very fine/ fine fine/medium medium/ coarse coarse/ very coarse 700 very coarse/ extremely coarse 600 XC 500 C VC 400 M 300 F 200 Drop Size (microns) VF 100 0 0.1 0.5 0.9 Cumulative Volume Fraction EPA Requested Changes Coming!!!! VMD

33. 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.

34. 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) 183-280µm • Medium (M) 281-429µm • Coarse (C) 430-531µm • Very Coarse (VC) 532-655µm • Extremely Coarse (XC) >656µm *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