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

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-$$$

Productivity The application triangle Off-site protection Efficacy

Status of EPA Label Guidance Proposal on Drift

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

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

Drift Labeling Guidance Issues EPA’s Proposal and Follow-up Draft Guidance for labeling statements for controlling spray and dust drift was published in the Federal Register (2001) and public comments have been received.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.

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!!!!!

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.

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!!!!

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

For more information contact www.epa.gov/pesticides www.epa.gov/pesticides/citizens/spraydrift.htm

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.

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.

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 Shelterbelts 5 0 5 10 15 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.

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 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)

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(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 VD0.1 (10%) VD0.9 (90%)

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

ASAE S-572 Droplet Size Standard

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

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

Computer Models:

AgDRIFT® Program Map

Example of Model Use – Aerial Applicators Standard Operation

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

Drift Reduction Additives: Many available! Not EPA regulated Long chain polymers New-soluble powders 50 - 80% reduction in off-target movement Pump shear problems Effect on the pattern?

Goodland Drift Project 8 Companies 19 Drift Reduction/Deposition Aids Water X-77 @ .25% 2 Airplanes AT 502 - 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

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

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.

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

Thank You

For more information contact: rewolf@ksu.edu www.bae.ksu.edu/rewolf/