technical aspects of spray drift reeves petroff montana state university extension pesticide...

Technical Aspects of Spray Drift

Technical Technical Aspects of Aspects of Spray DriftSpray Drift

Reeves PetroffMontana State University

Extension Pesticide EDUCATION Specialist


Why Interest in Drift?Why Interest in Drift? Spotty pest control Wasted chemicals Off-target damage Litigious Society Result-higher costs-$$$ More wind?? (Timing) Environmental impact

Water and Air Quality Public more aware of pesticide

concerns! (Negative)

Spraying in more populated areas? (Suburbs)


Big lies

The check is in the mail. I love you. There’s no wind on the drop zone. Always use the biggest drop possible. Its best to spray when there’s no wind Increase pressure to increase GPA


Nozzle Technology? Nozzles designed to reduce drift Improved drop size control Emphasis on ‘Spray Quality’


Nozzles are important:

Control the amount – GPA. Determine uniformity of application. Affects the coverage. Influences the drift potential.


Will affect drift: Movement of spray

particles off-target. Creating smaller

spray drops will result in increased drift.

Large droplets maybe result in bounce.

$64,000 Question?


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

chemicalformulationdrop sizeevaporation

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 is very important

Know the location of sensitive areas – consider..

Do not spray at any wind speed if it is blowing towards sensitive areas…

Spray when breeze is gentle, steady, and blowing AWAY from sensitive areas.

“Dead calm” conditions are recommended.

safe buffer zones.

---all nozzles can drift---

NEVER


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

Spray Droplet Size


Drift is Influenced by:Drift is Influenced by:

Size of the Spray Droplets -

Volume Median Diameter (VMD) Droplet Spectrum (Range - big to small)

Size of the Spray Droplets -

Volume Median Diameter (VMD) Droplet Spectrum (Range - big to small)

% Volume in droplets less than 200 microns in size

% Volume in droplets less than 200 microns in size


One micron (m) =1/25,000 inchOne micron (m) =1/25,000 inch

Relationship of Drift to Drop SizeRelationship of Drift to Drop Size


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


Nozzle Drop Size ClassesNozzle Drop Size Classes

Very Fine to Fine < 200 um

Medium to Coarse – 200 to 450 um

Very Coarse > 450 um


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


Important Droplet Statistics:

Operational Area


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


Cutting Droplet Size in Half

Cutting Droplet Size in Half

Results in Eight Times the Number of

Droplets

Results in Eight Times the Number of

Droplets

==2 more droplets fill in

the sphere2 more droplets fill in

the sphere

500Microns

500Microns 250

Microns


Spray Droplet Movement with Various Wind SpeedsDropletSizes(microns)

5 mphWind

10 mphWind

15 mphWind

20mphWind

100 24 ft. 48 ft. 72 ft. 96 ft.

200 9 18 26 35

400 5 9 14 18

500 4 7 10 14

600 3 6 9 12

Boom height: 3 feet


Wind Speeds Gradients

The relation between height above the canopy of a crop and the speed of wind.

30

20

10

6

2

0

11 mph

10 mph

8 mph

7 mph

5 mph

Hei

gh

t A

bo

ve C

rop

Can

op

y, F

eet

Wind Speed


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


Wind Patterns Near Shelterbelts

Distance from shelterbelt (tree heights)

Generalized pattern of wind in the neighborhood of a shelterbelt.

5 0 5 10 15

Hei

gh

t


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)


Wind Patterns Around Buildings

Diagram of Wind Around a BuildingAdapted From Farm Structures*

OverheadView

WindWind

* H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)


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 rises and mixes 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:


Temperature increases with altitude. 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:


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.


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

Notice smoke or dust patterns to

identify inversion conditions.


Evaporation and Deceleration of Various Size Droplets*Droplet

Diameter(microns)

TerminalVelocity(ft/sec)

Final Dropdia.

(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


Evaporation of Droplets

Wind

High Relative HumidityLow Temperature

Low Relative HumidityHigh Temperature

Fal

l Dis

tanc

e


Spray Characteristics are Important to Understand:

Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind


Tip Spray Selection by Drop Size

Turbo TeeJet Flat-fan


XR Flat-fan @ 20, 40, & 80 psi Turbodrop XL @ 20, 40, & 80 psi


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, electrostatics, air-assist


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.


In Conclusion:

Minimizing spray drift is in Minimizing spray drift is in the best interests of the best interests of

everyone. Do your part to everyone. Do your part to keep pesticides on target.keep pesticides on target.

Minimizing spray drift is in Minimizing spray drift is in the best interests of the best interests of

everyone. Do your part to everyone. Do your part to keep pesticides on target.keep pesticides on target.


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