Understanding Spray Understanding Spray DriftDrift

Robert E. WolfExtension Specialist

Application Technology

Why Interest in Drift?Why Interest in Drift?

Spotty pest control Wasted chemicals Off-target damage Litigious Society ???? Result - higher costs - $$$ Windy?? (Timing) Environmental impact (Water and Air Quality)

Spotty pest control Wasted chemicals Off-target damage Litigious Society ???? Result - higher costs - $$$ Windy?? (Timing) Environmental impact (Water and Air Quality)

Misapplication Facts:

2%8%

24%

33%

33%

Equipment

Drift

Tank Mix

Wrong Field

Off Label

Facts about drift:

13%

26%

38%

23%

Nozzle

Applicator

Physical

Other

Why is the Nozzle Important?

Amount of spray appliedUniformity of the sprayCoverage on the targetAmount of off-target drift

Technical Aspects of Spray Drift

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

releaseWeather

air movement (direction and velocity)

temperature and humidity air stability/inversions topography

Wind Direction: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.

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)

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:Inversions:

Under these conditionsthe 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:Temperature Inversions:

Recognizing Inversions: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.

Cloud of 5-25 u oil droplets generated under unstable conditions

105 foot temperature monitoring tower

8’ 41°F

16’ 41°F

32’ 40°F

64’ 40°F

105’ 38°F

8’ 33°F16’ 36°F32’ 37°F64’ 38°F

105’ 38°F

.5 mph wind

2.5 mph wind

Shallow surface inversionSTABLE conditions up to 64’ NEUTRAL conditions at 105’

Cloud is dispersing

Precautions for Inversions: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.

Wind Patterns Near Treelines:

Adapted from Survey of Climatology:Griffiths and Driscoll,

Texas A&M University, 1982

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)

Spray Droplet SizeSpray Droplet Size

Particle drift will result from the smaller drops created during the spray process. The size of the droplets created is critical.

Dropsizes are measured in microns using laser beams.

Drift & Dropsize Relationship:

Dropsize Facts:

One micron = 1/25,000 inchExpressed as (VMD) Volume Median DiameterExample - VMD = 500 microns

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

Raindrop compared to a Turbo Turf FloodRaindrop compared to a Turbo Turf Flood

Raindrop DropTurbo Turf Flood

5.0 MPH wind at 40 psi

1/2 of spray volume = larger droplets1/2 of spray volume = larger droplets

VMDVMD

1/2 of spray volume = smaller droplets1/2 of spray volume = smaller droplets

Cutting Droplet Size in HalfResults in Eight Times the Number of Droplets

Cutting Droplet Size in HalfResults in Eight Times the Number of Droplets

500Microns

500Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

250Microns

Important Droplet Statistics:Important Droplet Statistics:

Operational Area

Evaporation of DropletsEvaporation of Droplets

Wind

High Relative HumidityLow Temperature

Low Relative HumidityHigh Temperature

Fal

l Dis

tanc

e

Strategies to Reduce Drift: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 adverse weather conditions Consider using buffer zones Consider using new technologies:

• drift reduction nozzles• drift reduction additives• shields

Drift Reduction Additives:Drift Reduction Additives:

Many available! Not EPA regulated Long chain polymers New-soluble powders 50 - 80% reduction in

off-target movement Pump shear problems

Example Reference Graph

Cumulative Volume Fraction

0.1 0.5 0.9

Drop S

ize (microns) 0

100

200

300

400

500

600

700

800

900

very fine/ fine fine/mediummedium/ coarsecoarse/ very coarsevery coarse/ extremely coarse

VF

F

M

CVC

XC

New Label language-EPA Reviewing Public Comments

Public ‘Listening Sessions’ planned

Sometime in 2003?? Match the crop

protection product to the target

Adhere to label guidelines based on an industry standard • ASAE S-572

Buffer Zones or No Spray Zones

Maximize Efficacy Minimize Drift

EPA Requested Changes Coming!!!!EPA Requested Changes Coming!!!!

Example Reference Graph

Cumulative Volume Fraction

0.1 0.5 0.9

Dro

p S

ize

(mic

rons

)

0

100

200

300

400

500

600

700

800

900

very fine/ fine fine/mediummedium/ coarsecoarse/ very coarsevery coarse/ extremely coarse

VF

F

M

CVC

XC

For more information contact:For more information contact:

www.bae.ksu.edu/rewolf/

rewolf@ksu.edu