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

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

Technical Aspects of Spray Drift Nozzle Technology? u Nozzles designed to reduce drift u Improved drop size control u Emphasis on ‘Spray Quality’

Technical Aspects of Spray Drift Nozzles are important: u Control the amount – GPA. u Determine uniformity of application. u Affects the coverage. u Influences the drift potential.

Technical Aspects of Spray Drift Will affect drift: u Movement of spray particles off-target. u Creating smaller spray drops will result in increased drift. u Is it Coverage vs Drift? u 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

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

Technical Aspects of Spray Drift 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

Technical Aspects of Spray Drift Wind Direction: u 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.

Technical Aspects of Spray Drift u 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. u Drift potential is lowest at wind speeds between 3 and 10 mph (gentle but steady breeze) blowing in a safe direction. However, Drift Potential May be High at Low Wind Speeds

Technical Aspects of Spray Drift Spray Droplet Movement with Various Wind Speeds

Technical Aspects of Spray Drift Wind Speeds Gradients The relation between height above the canopy of a crop like cotton or soybean and the speed of wind mph 10 mph 8 mph 7 mph 5 mph Height Above Crop Canopy, Feet Wind Speed

Technical Aspects of Spray Drift Wind Current Effects u Wind currents can drastically affect spray droplet deposition u Structures drastically affect wind currents  Wind breaks  Tree lines and orchards  Houses and barns  Hills and valleys

Technical Aspects of Spray Drift Wind Patterns Near Shelterbelts Distance from shelterbelt (tree heights) Generalized pattern of wind in the neighborhood of a shelterbelt Height

Technical Aspects of Spray Drift Wind Patterns Near Treelines Adapted from Survey of Climatology: Griffiths and Driscoll, Texas A&M University, 1982

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

Technical Aspects of Spray Drift Wind Patterns Around Buildings Diagram of Wind Around a Building Adapted From Farm Structures* Overhead View Wind * H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)

Technical Aspects of Spray Drift NameFeaturesCost* DwyerFloating Ball15.50 Wind WizardMechanical39.50 Turbo MeterWind speed - knots, feet/min, meters/sec, mph Kestrel 1000Maximum, average, current wind speed - knots, feet/min, meters/sec, mph Kestrel 2000Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec, mph Kestrel 3000All wind speed features plus temp, wind chill, dew point, heat index, relative humidity Plastimo Iris 50**Compass89.00 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( )

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

Technical Aspects of Spray Drift 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. Temperature Inversion Altitude Temperature increases with height Warm Air Cool Air Increasing Temperature Temperature Inversions:

Technical Aspects of Spray Drift Recognizing Inversions: u Under clear to partly cloudy skies and light winds, a surface inversion can form as the sun sets. u Under these conditions, a surface inversion will continue into the morning until the sun begins to heat the ground.

Technical Aspects of Spray Drift Courtesy – George Ramsay, Dupont

Technical Aspects of Spray Drift Precautions for Inversions: u Surface inversions are common. u 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 u Use of a smoke bomb or smoke generator is recommended to identify inversion conditions.

Spray Droplet Size

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

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

Technical Aspects of Spray Drift Comparison of Micron Sizes for Various Items: (approximate values) u pencil lead 2000 (  m ) u paper clip 850 (  m ) u staple 420 (  m ) u toothbrush bristle 300 (  m ) u sewing thread150 (  m ) u human hair100 (  m ) 150

Technical Aspects of Spray Drift 1/2 of spray volume = larger droplets VMD 1/2 of spray volume = smaller droplets

Technical Aspects of Spray Drift Cutting Droplet Size in Half Results in Eight Times the Number of Droplets 500 Microns 500 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns 250 Microns

Technical Aspects of Spray Drift Important Droplet Statistics: Operational Area

Technical Aspects of Spray Drift Evaporation of Droplets Wind High Relative Humidity Low Temperature Low Relative Humidity High Temperature Fall Distance

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

Technical Aspects of Spray Drift XR 40, 80 PSI Turbodrop 40, 80 PSI Boom Drift

Technical Aspects of Spray Drift Example Reference Graph Cumulative Volume Fraction Drop Size (microns) very fine/ fine fine/medium medium/ coarse coarse/ very coarse very coarse/ extremely coarse VF F M C VC XC u New Label language- EPA Reviewing Public Comments u Public ‘Listening Sessions’ planned u Sometime in 2003?? u Match the crop protection product to the target u Adhere to label guidelines based on an industry standard  ASAE S-572 u Buffer Zones or No Spray Zones u Maximize Efficacy u Minimize Drift EPA Requested Changes Coming!!!!

Technical Aspects of Spray Drift Origin Of Standardized Spray Droplet Size Categories u 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.

Technical Aspects of Spray Drift ASAE DSC and Volume Median Diameter (D V0.5 ) From PMS* Laser Spectrometer u Very Fine (VF) < 182µm u Fine (F) µm u Medium (M) µm u Coarse (C) µm u Very Coarse (VC) µm u Extremely Coarse (XC) >656µm *USDA ARS College Station, TX Droplet Spectra Classification (DSC) Droplet Size Range

Technical Aspects of Spray Drift

Computer Models:

Technical Aspects of Spray Drift AgDRIFT® Program Map

Technical Aspects of Spray Drift Example of Model Use - Aerial: Applicators Standard Operation

Technical Aspects of Spray Drift Strategies to Reduce Drift: u Select nozzle to increase drop size u Increase flow rates - higher application volumes u Use lower pressures u Use lower spray (boom) heights u Avoid adverse weather conditions u Consider using buffer zones u Consider using new technologies:  drift reduction nozzles  drift reduction additives  shields, electrostatics, air-assist

Technical Aspects of Spray Drift 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.

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

Technical Aspects of Spray Drift