Herbicide Drift Management
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Herbicide Drift Management. John Boyd University of Arkansas. What is drift?. Movement of spray particles and/or vapors off-target. Types of Drift. Vapor Drift - associated with volatilization, gases and fumes. Particle Drift - movement of spray particles. Misapplication Facts. 2%.

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Herbicide Drift Management

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Herbicide drift management

Herbicide Drift Management

John Boyd

University of Arkansas


Herbicide drift management

What is drift?

Movement of spray particles and/or vapors off-target.


Types of drift

Types of Drift

  • Vapor Drift - associated with volatilization, gases and fumes.

  • Particle Drift - movement of spray particles.


Misapplication facts

Misapplication Facts

2%

8%

Equipment

33%

Drift

Tank Mix

24%

Wrong Field

Off Label

33%

Source: Farmland Insurance 1996


Contributions to drift

Contributions to Drift


Factors affecting drift

Factors Affecting Drift


Weather other factors affecting drift

Weather & other Factors Affecting Drift

  • Temperature & humidity

  • Wind (direction and velocity)

  • Air stability/inversions

  • Topography


Drift potential depends on

Drift Potential Depends on

  • 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.


Droplet size

Droplet Size

  • Spray drift droplets are measured in microns and expressed as Volume Median Diameter or VMD

  • One micron = 1/25,000th inch


Comparison of micron sizes

Comparison of Micron Sizes


Herbicide drift management

1/2 of spray volume = smaller droplets

VMD

1/2 of spray volume = larger droplets


Cutting droplet size in half

Cutting Droplet Size in Half

Results in Eight Times the Number of Droplets

=

250

Microns

500

Microns

2 more droplets fill in the sphere


Important droplet statistics

Important Droplet Statistics:

VMD

(50%)

Operational Area

VD0.9

(90%)

VD0.1

(10%)


Evaporation and deceleration of various size droplets

Evaporation and Deceleration of Various Size Droplets*

Droplet

Terminal

Final Drop

Time to

Deceleration

Diameter

Velocity

diameter

evaporate

distance

(microns)

(ft/sec)

(microns)

(sec)

(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


Nozzle drop size classification british crop protection council bcpc

Size

Very

Fine

Medium

Coarse

Very

Fine

Coarse

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)


Drop size classification use

Drop Size Classification & Use

  • Very Fine

  • Fine

  • Medium

  • Coarse

  • Very Coarse

  • <119 m

  • 119-216 m

  • 217-353 m

  • 354-464 m

  • >464 m

Insecticides

and Fungicides

Herbicides and

Postemergence

Soil Applications

of Herbicides


Herbicide drift management

Software for estimating droplet size distribution is available on the web.

http://apmru.usda.gov/downloads/downloads.htm


Evaporation of droplets

Evaporation of Droplets

High Relative Humidity

Low Temperature

Low Relative Humidity

High Temperature

Fall Distance

Wind


Herbicide drift management

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.


Drift potential may be high at low wind speeds

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.


Conditions

Conditions

  • Where are what are the adjacent crops?

  • Are there houses, a town or other sensitive areas near the site?


Buffer zone

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)


Product selection

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.


Equipment selection and setup

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.


When planning a spray application

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.


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 arenever recommended.


However drift potential may be high at low wind speeds

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.


Herbicide drift management

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)


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.


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.


Nozzles are important

Nozzles are important

  • Control the amount – GPA.

  • Determine uniformity of application.

  • Affects the coverage.

  • Influences the drift potential.


Spray characteristics are important to understand

Spray Characteristics are Important to Understand

Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind


Herbicide drift management

XR Flat-fan @20, 40, 80 PSI

Turbodrop XL @20, 40, 80 PSI

Boom

Drift


Strategies to reduce drift

Strategies to Reduce Drift

  • Increased drop size.

  • Higher application volumes.

  • Lower pressure.

  • Avoid adverse weather conditions.


Strategies to reduce drift1

Strategies to Reduce Drift

  • Buffer zones.

  • Drift reduction nozzles

  • Drift reduction additives

  • Consider using new technologies:

    • drift reduction nozzles


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