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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