Spray Drift – What causes it and how to avoid it

Tom WolfAgriMetrix Research and Training

Saskatoon, SK

agrimetrix@gmail.com@Nozzle_Guy

Pesticide Applicator CertificationFor: Professional Development Solutions

Drift – The Ambassador of Spraying

Application Goals

3 Es of Pesticide

ApplicationEffectiveEfficientEnvironmentalNorman Morgan

Airborne movement of droplets or vapours

from the treated area

Airborne movement of droplets or vapours

from the treated area

Spray Drift

Droplet drift usually occurs within minutes of the application, vapour

drift can occur minutes or days after application

Droplet drift usually occurs within minutes of the application, vapour

drift can occur minutes or days after application

On-Swath Deposit

0

20

40

60

80

100

120

Med Coarse Fine Med X. Coarse

XR80-03 AIXR110-025 XR110-04 XR110-05 DR110-05

On

-sw

ath

de

po

sit

(% o

f ap

plie

d) Low boom

Slow speedHigh boomFast speed

5-120 m5 m2 m

1.7%

5%82%

100%

0.3%

Drift Spray Accountancy

On Target Off Target

1 m

10% 1%

45 M kg x 80% sprayed x 1.7% airborne loss

=

612,000 kg

The Size of the Problem

Drift Patterns

0

2

4

6

8

10

12

0 50 100 150

Distance (m)

Deposit

(%

of em

itte

d)

Deposit Patterns

Drift Causes

Small Droplet

sWind Drift!

Droplet drift

Wind speed

Atmospheric turbulence- thermal- mechanical

Droplet size

Droplet velocity- sprayer type- pressure

Initial size- sprayer type- nozzle type, size- pressure- formulation

Rate of evaporation- temperature- RH

Transit time- velocity- boom height

Factors Involved in Spray Drift

What Causes Drift?

Low Energy

Exposure to Force Movement

Strategy

Low Energy

• Increase size• Increase velocity

• e.g. low drift nozzles, air assist

Exposure to Force

• Protect• Decrease

exposure time• e.g. shrouds, low

booms, slow travel

Areas of unequal pressure create vortices which remove small droplets from the spray

cloud

Nozzle selection Sprayer settings

Focus is droplet size and boom height

Reducing the Problem

Dri

ft P

oten

tial

0

10

20

30

40

50

ER

8003

DR

8003

80015

8003

8006

8003

11003

SR

8003

20 psi

40 psi

75 psi

NozzleType

FlowRate

FanAngle

SprayPressure

Drift Potential

Droplet Size Distributions

028.57143

48.3965

68.22157

88.04665

107.87172

127.69679

147.52187

167.34694

187.17201

206.99709

226.82216

246.64723

266.47231

286.29738

306.12245

325.94753

345.7726

365.59767

385.42275

405.24782

425.07289

444.89797

464.72304

484.54811

504.37319

524.19826

544.02333

563.84841

583.67348

603.49855

623.32363

643.1487

662.97377

682.79885

702.62392

722.44899

742.27407

762.09914

781.92421

801.74928

821.57436

841.39943

861.2245

881.04958

900.87465

920.69972

940.5248

960.34987

980.17494

1000.00002

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

ER11006 40 psi

SR11006 40 psi

Droplet diameter (µm)

Vo

lum

e

Spray Quality

Field Tests

Flexi-Coil Field Sprayer

XR8003, 40 psi AI110025, 58 psi

Application volume = 100 L/haTravel speed = 13 km/h

Medium

VeryCoarse

Field SprayerTravel speed 13.0 km/h, Application volume 100 L/ha

Wind speed (km/h)

0 4 8 12 16 20 24 28 32

Air

bo

rne

dri

ft A

t 5

m (

% o

f em

itte

d)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

XR8003y = -0.85 + 0.18 xr2 = 0.79

AI110025y = -0.16 + 0.04 xr2 = 0.72

TT11005, 40 psi AI11004, 64 psi

Gregson High-Clearance SprayerGregson High-Clearance Sprayer

Application volume = 100 L/haTravel speed = 22.5 km/h

High ClearanceTravel speed 22.5 km/h, Application volume 100 L/ha

Wind speed (km/h)

0 4 8 12 16 20 24 28 32

Air

bo

rne

dri

ft A

t 5

m (

% o

f em

itte

d)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

TT11005y = -0.46 + 0.16 xr2 = 0.97

AI11004y = 0.46 + 0.05 xr2 = 0.76

Boom Height

Drift potential doubles for higher boom Use auto boom-height controller

“Auto-Boom”

Reduced Spray Pressure?

Conventional flat fans 20 - 40 psi

Pre-orifice 30 - 50 psi

Air-Induced 40 – 60 psi (low-pressure

type) 60 – 80 psi (high

pressure type)

Ensure that patterns are optimal

Droplet Velocity (Energy)

Droplet Velocity Distributions

0 200 400 600 800 1000 12000

2

4

6

8

10

12

14

16

Droplet diameter (µm)

Velo

cit

y

Principle of HARDI TWIN air assistance

Air Off Air On

Drift- at various wind speeds(data from Hardi)

1.5 3 4.5 8.50.0

1.0

2.0

3.0

4.0

5.0

100 l/ha, 4110-12, 2,5 bar, 7,7 km/h.

Conv.

Air Assist

Wind velocity, m/s

% d

rift

Little Drift Lots of Drift

Courtesy of Paul Miller, SRI

Models and Regulations

New Buffer Zone Label Language

Untreated (Buffer Zone)

20 mConventional application

15 mLow-drift application

untreated

5 mVery low-drift application

untreated

“Do not apply with spray droplets smaller than ASAE medium classification”

“…When using a shroud, BZ can be reduced by 70%...”

Buffer Zone Calculator

http://www.hc-sc.gc.ca/cps-spc/pest/agri-commerce/drift-

derive/index-eng.php

Atmospheric Conditions

Courtesy George Ramsey, DuPont

Daily Wind Pattern

Time of day (h)

Win

d s

pe

ed a

t 1

m h

eig

ht

(m/s

)

0

1

2

3

4

5

6

7

8

0 4 8 12 16 20 24

Mechanical Turbulence

Thermal Turbulence

Unstable (Desirable normal daytime conditions)

Stable(inversion)

Spray cloud disperses, moving upward and downwind

Spray cloud hangs over treated area in high concentration

Warm Soil

Cold soil

Cold air - dense, still

Warm, still air

Inversion Conditions

Dispersion

Hei

gh

t

TemperatureH

eig

ht

Temperature

Unstable Stable (Inversion)

3 pm 11 pm

Sunset10 pm

3 am 5 am

Sunrise5 am

7 am 8 am 9 am 3 pm

Temperature

Hei

ght

3 pm 11 pm

Sunset10 pm

3 am 5 am

Sunrise5 am

7 am 8 am 9 am 3 pm

Wind

Calm conditions not well suited for spraying unpredictable wind

direction

sometimes mistaken for inversions

Low, steady winds ideal Predictable direction

Dilution of spray cloud

High winds increase total loss, but do not always increase deposits

Delta T (droplet evaporation)

Most Important Factors Governing Drift

Trained, conscientious operator

Communication / Relationships

Weather Conditions Spray Quality Shrouds Boom Height Travel Speed