1 herbicide drift management john boyd university of arkansas
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Herbicide Drift Management
John Boyd
University of Arkansas
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Movement of Movement of spray particles spray particles and/or vapors and/or vapors off-target.off-target.
What is drift?
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Types of Drift
Vapor DriftVapor Drift - associated with volatilization, gases and fumes.
Particle DriftParticle Drift - movement of spray particles.
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Misapplication Facts2%
8%
24%
33%
33%
Equipment
Drift
Tank Mix
Wrong Field
Off Label
Source: Farmland Insurance 1996
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Contributions to Drift
13%
26%
38%
23% Nozzle
Applicator
Physical
Other
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Factors Affecting Drift
Spray Characteristics
Equipment & Application
Herbicide Nozzle type
Formulation Nozzle size
Additives Nozzle orientation
Drop size Nozzle pressure
Evaporation Height of release
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Weather & other Factors Affecting Drift
Temperature & humidity Wind (direction and velocity) Air stability/inversions Topography
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Drift Potential Depends Drift Potential Depends onon
The percentage of small droplets in the droplet size range.
Droplet size is measured in microns.
The key factor is the percentage of the spray droplets less than 200 microns in diameter.
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Droplet Size
Spray drift droplets are measured in microns and expressed as Volume Median Diameter or VMD
One micron = 1/25,000th inch
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Comparison of Micron Sizes
100 microns Human hair
150 microns Sewing thread
300 microns Toothbrush bristle
420 microns Staple
850 microns Paper clip
2000 microns #2 Pencil lead
121/2 of spray volume = larger droplets
VMD
1/2 of spray volume = smaller droplets
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Cutting Droplet Size in Half
Results in Eight Times Results in Eight Times the Number of Dropletsthe Number of Droplets
==2 more
droplets fill in the sphere
500Microns
500Microns
250Microns
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Important Droplet Statistics:
Operational Area
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Evaporation and Deceleration of Various Size Droplets*
DropletDiameter(microns)
TerminalVelocity(ft/sec)
Final Dropdiameter(microns)
Time toevaporate
(sec)
Decelerationdistance
(in)
20 .04 7 0.3 <1
50 .25 17 1.8 3
100 .91 33 7 9
150 1.7 50 16 16
200 2.4 67 29 25
*Conditions assumed: 90 F, 36% R.H., 25 psi., 3.75% pesticide solution
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Size VeryFine
Fine Medium Coarse VeryCoarse
Dv0.1 <55* 55-94 95-164 165-225 >225
Dv0.5 <119 119-216 217-353 354-464 >464
Dv0.9 <204 204-369 370-598 599-789 >789
%<141 57.2 20.2-57.2 5.7-20.1 2.9-5.6 <2.9
*Numbers listed are in Microns
Nozzle Drop Size ClassificationBritish Crop Protection Council (BCPC)
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Drop Size Classification & Use
Very Fine Fine Medium Coarse Very
Coarse
<119 m 119-216
m 217-353
m 354-464
m >464 m
Insecticidesand Fungicides
Herbicides andPostemergence
Soil Applications of Herbicides
18http://apmru.usda.gov/downloads/downloads.htm
Software for estimating droplet size distribution is available on the web.
Evaporation of Droplets
Wind
High Relative HumidityLow Temperature
Low Relative HumidityHigh Temperature
Fal
l Dis
tanc
e
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Wind 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.
Spraying in dead calm conditions is never recommended.
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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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Conditions
Where are what are the adjacent crops?
Are there houses, a town or other sensitive areas near the site?
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Buffer Zone A buffer zone means an area where
pesticide is not directly applied thereby providing protection to a defined area.
Buffer zones may depend on: state regulations pesticide product labels prevailing weather conditions sensitive/protected area(s)
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Product Selection You may have several options on
products. Understand the product chemistry! Consider the effect this product
may have on homes and gardens near the application site.
Consider environmental and wildlife safety.
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Equipment Selection and Setup
Select equipment to produce the largest droplet size possible and still provide adequate coverage.
Be aware that some products require relatively smaller droplets to ensure good coverage.
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When Planning a Spray Application
Allow enough time for planning and executing the operation. Including weather and equipment delays.
Do not 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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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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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.
However, Drift Potential May be High at Low Wind Speeds
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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)
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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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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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Nozzles are important
Control the amount – GPA. Determine uniformity of
application. Affects the coverage. Influences the drift potential.
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Spray Characteristics are Important to Understand
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
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XR Flat-fan @20, 40, 80 PSI Turbodrop XL @20, 40, 80 PSI
Boom
Drift
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Strategies to Reduce Drift
Increased drop size. Higher application volumes. Lower pressure. Avoid adverse weather
conditions.
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Strategies to Reduce Drift
Buffer zones. Drift reduction nozzles Drift reduction additives Consider using new technologies:
drift reduction nozzles