1. Spray Drift – What causes it and how to avoid it
Pesticide Applicator Certification
For: Professional Development Solutions
Tom Wolf
AgriMetrix Research and Training
Saskatoon, SK
@Nozzle_Guy 1 1

2. Drift – The Ambassador of Spraying

3. 3 Es of Pesticide Application
Application Goals
3 Es of Pesticide Application
Effective
Efficient
Environmental
Norman Morgan 2 2

4. Airborne movement of droplets or vapours from the treated area
Spray Drift
Airborne movement of droplets or vapours from the treated area
Droplet drift usually occurs within minutes of the application, vapour drift can occur minutes or days after application

5. On-Swath Deposit
Low boom Slow speed
High boom Fast speed

6. Drift Spray Accountancy
100%
1.7%
2 m
5-120 m
5 m
1 m
82%
10% 5% 1%
0.3%
On Target
Off Target

7. 45 M kg x 80% sprayed x 1.7% airborne loss
The Size of the Problem
45 M kg x 80% sprayed x 1.7% airborne loss =
612,000 kg

8. Drift Patterns

9. Deposit Patterns

12. Drift Causes

13. Small Droplets
Wind
Drift!

14. Factors Involved in Spray 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
Droplet drift

15. What Causes Drift?
Low Energy
Exposure to Force
Movement

16. Exposure to Force Low Energy Strategy 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

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

20. Focus is droplet size and boom height
Reducing the Problem
Nozzle selection
Sprayer settings
Focus is droplet size and boom height

21. Drift Potential Drift Potential 50 80015 11003 40 75 psi 30 40 psi
Spray
Pressure
Fan
Angle
Flow
Rate
Nozzle
Type 50
80015
11003 40
75 psi 30
40 psi
8003
8003
ER8003
Drift Potential 20
20 psi
8006
SR8003 10
DR8003

22. Droplet Size Distributions
Let’s talk about how we describe droplet size. Here is a typical distribution of spray volume in an agricultural spray, using a conventional nozzle (red). Note that the spray contains both very small (10 µm) and very large (1000 µm) droplets. The majority of the spray volume is in intermediate sized droplets between 200 and 500 µm
When we lower the pressure (or change to a low-drift nozzle), we still retain the same large span of droplet diameters ranging from 10 to 1000 µm (blue bars). But now, the distribution has shifted to the right. This means less volume in small droplets (less drift), more volume in large droplets. The majority of the dose remains in the middle region, but more of it is in the larger droplets. As long as we don’t go too far with coarseness, we’re OK.
All low-drift nozzles operate on the same basic principle (internal pressure drop creating larger droplets). 22

23. Spray Quality

24. Field Tests

25. Flexi-Coil Field Sprayer
Application volume = 100 L/ha
Travel speed = 13 km/h
XR8003, 40 psi
AI110025, 58 psi

26. Medium 26

27. Very Coarse
At 40 psi, spray quality is starting to be good for general weed control 27

29. Gregson High-Clearance Sprayer
Application volume = 100 L/ha
Travel speed = 22.5 km/h
TT11005, 40 psi
AI11004, 64 psi

31. Boom Height Drift potential doubles for higher boom
Use auto boom-height controller

32. “Auto-Boom”

33. Reduced Spray Pressure?
Conventional flat fans
psi
Pre-orifice
psi
Air-Induced
40 – 60 psi (low-pressure type)
60 – 80 psi (high pressure type)
Ensure that patterns are optimal

34. Droplet Velocity (Energy)

35. Droplet Velocity Distributions
Spray velocity tends to slow down with coarser sprays, due to the lower internal pressures of these nozzles. This means that large drops from a low-drift nozzle are more easily retained than the large drops from conventional nozzles – a good thing. 35

37. Principle of HARDI TWIN air assistance

39. Air Off
Air On

40. Drift- at various wind speeds (data from Hardi)

41. Little Drift
Lots of Drift

43. Models and Regulations
Courtesy of Paul Miller, SRI

44. New Buffer Zone Label Language
Untreated (Buffer Zone)
20 m
Conventional application
15 m
Low-drift application
untreated
5 m
Very low-drift application
untreated

45. “Do not apply with spray droplets smaller than ASAE medium classification”
“…When using a shroud, BZ can be reduced by 70%...”

47. Buffer Zone Calculator

55. Example

57. Atmospheric Conditions
Courtesy George Ramsey, DuPont

58. Daily Wind Pattern Time of day (h) Wind speed at 1 m height (m/s) 8 76 5 4
Wind speed at 1 m height (m/s) 3 2 1 4 8 12 16 20 24
Time of day (h)

59. Mechanical Turbulence

60. Thermal Turbulence

61. Inversion Conditions Dispersion
Spray cloud disperses, moving upward and downwind
Unstable (Desirable normal daytime conditions)
Warm Soil
Inversion Conditions
Disapppears after sunrise and 2-3 degree increase in temperature.
Warm, still air
Spray cloud hangs over treated area in high concentration
Stable (inversion)
Cold air - dense, still
Cold soil

62. Unstable
Stable (Inversion)
Height
Temperature
Height
Temperature

63. Height Temperature 3 pm 11 pm 3 am 5 am 7 am 8 am 9 am 3 pm
Sunset 10 pm
3 am
5 am
Sunrise 5 am
7 am
8 am
9 am
3 pm
Height
Temperature

64. 3 pm
11 pm
Sunset 10 pm
3 am
5 am
Sunrise 5 am
7 am
8 am
9 am
3 pm

70. 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

72. Delta T (droplet evaporation)

73. Most Important Factors Governing Drift
Trained, conscientious operator
Communication / Relationships
Weather Conditions
Spray Quality
Shrouds
Boom Height
Travel Speed