Understanding Spray Drift

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Understanding Spray Drift

• Robert E. Wolf
• Extension Specialist Application Technology

Biological and Agricultural Engineering
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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-

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Productivity
The application triangle
Off-site protection
Efficacy
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Status of EPA Label Guidance Proposal on Drift
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Spray Drift Task Force

• April 1990
• 38 Companies
• 20 Million
• 21 Studies
• Airblast, Aerial,
• Ground, Chemigation
• 40 Reports
• Downwind!!!!
• Droplet size!!!!

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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

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Drift Labeling Guidance Issues
EPAs 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• Draft Guidance for labeling statements for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.

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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!!!!!

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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????

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So Whats Happening Now??

• In the mean time, registrants can
• Go with the current draft labeling.
• Propose something else thats at least as
  protective that EPA will accept.
• Go with previous labeling guidelines.
• Go with old standard do not allow drift.
• Trial statements!!!!

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EPA and Drift!
EPAs 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

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For more information contact
www.epa.gov/pesticides
www.epa.gov/pesticides/citizens/spraydrift.htm
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Technical Aspects of Spray Drift
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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

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Types of Drift

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

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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

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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.

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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.

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Spray Droplet Movement with Various Wind Speeds
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Wind Speeds Gradients
Wind Speed
The relation between height above the canopy of a
crop like cotton or soybean and the speed of wind.
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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

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Wind Patterns Near Shelterbelts
Distance from shelterbelt (tree heights)
Generalized pattern of wind in the neighborhood
of a shelterbelt.
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Wind Patterns Near Treelines
Adapted from Survey of Climatology Griffiths and
Driscoll, Texas AM University, 1982
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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)
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Wind Patterns Around Buildings
Diagram of Wind Around a Building Adapted From
Farm Structures
H.J. Barre and L.L. Sammet, Farm Structures
(Wiley, 1959)
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Wind Meters and Compass
Prices for Wind Meters taken from Gemplers 2002
Master Catalog Plastimo Airguide Inc., 1110
Lake Cook Road, Buffalo Grove, IL
60089(708-215-7888)
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Inversions
Under normal conditions air tends to rise and mix
with the air above. Droplets will disperse and
will usually not cause problems.
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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.
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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.

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Courtesy George Ramsay, Dupont
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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.

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Spray Droplet Size
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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
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Relationship of Drift to Drop Size
One micron (?m) 1/25,000 inch
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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
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1/2 of spray volume smaller droplets
VMD
1/2 of spray volume larger droplets
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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
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Important Droplet Statistics
VMD (50)
Operational Area
VD0.9 (90)
VD0.1 (10)
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Evaporation of Droplets
High Relative Humidity Low Temperature
Low Relative Humidity High Temperature
Fall Distance
Wind
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Spray Characteristics are Important to Understand
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
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ASAE S-572 Droplet Size Standard
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Coverage

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

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ASAE DSC and Volume Median Diameter (DV0.5) From
PMS Laser Spectrometer
Droplet Spectra Classification (DSC)
Droplet Size Range

• Very Fine (VF) lt 182µm
• Fine (F) 183-280µm
• Medium (M) 281-429µm
• Coarse (C) 430-531µm
• Very Coarse (VC) 532-655µm
• Extremely Coarse (XC) gt656µm

USDA ARS College Station, TX
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(No Transcript)
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Computer Models
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AgDRIFT Program Map
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Example of Model Use Aerial Applicators
Standard Operation
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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

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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?

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Goodland Drift Project

• 8 Companies
• 19 Drift Reduction/Deposition Aids
• Water
• X-77 _at_ .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

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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
• Rosens
• Precison Labs
• SanAg

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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.
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In Conclusion
Minimizing spray drift is in the best interests
of everyone. Do your part to keep applications
on target.
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Thank You
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For more information contact
rewolf_at_ksu.edu
www.bae.ksu.edu/rewolf/