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

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

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.

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

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

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

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

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.

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.

Wind Speeds Gradients Wind Speed Height Above Crop Canopy, Feet 30 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.

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.

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

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)

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(708-215-7888)

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.

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.

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.

Courtesy – George Ramsay, Dupont

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.

Spray Droplet Size

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

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

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 9

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

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

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

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

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

XR Flat-fan @20, 40, 80 PSI Turbodrop XL @20, 40, 80 PSI Boom Drift

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

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.

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) 183-280µm Medium (M) 281-429µm Coarse (C) 430-531µm Very Coarse (VC) 532-655µm 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

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

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

Thank You