This talk was given at the Innovations in Invasive Species Management Conference in Coeur d'Alene, Idaho, held from December 10-12, 2019. Abstract: Conventional backpack sprayers and nozzles use technology adapted from agricultural spraying systems. In the context of managing natural areas and invasive plants, however, this can be problematic, especially at sites with desirable native plants. Conventional spray systems are designed to be used with high pressure. High pressure produces greater quantities of tiny spray drops. These tiny spray drops can easily move off-target, carried by the wind and even air currents created by the act of spraying. This presentation discusses new results from ongoing tests of the Precision Electronic Dispenser from Green Shoots®. The Precision Electronic Dispenser uses ultra-low pressure (generally under about 10 psi) to deliver an herbicide mixture either as an aqueous foam or as liquid spray drops. The potential benefits of ultra-low pressure include: lowering herbicide usage; reducing mortality of nearby desirable plants; and minimizing exposure of workers and the broader environment.

1. Precision Applications of Herbicide Spray and
Foam
John Lampe
Coeur d'Alene, IdahoDecember 12, 2019
Innovations in Invasive Species Management

2. Most herbicide spray
technologies have been
adapted from agriculture.
.

3. Precision herbicide application not important with
genetically-modified, herbicide-resistant corn.
Corn
WeedsWeeds

4. Native area
management is
different.

5. Native plants are
not herbicide
resistant.

6. Native plants are
valuable:
• Forbs can live 3-25
years
• Grasses can live 5-39
Laurenroth et al.
2008.

7. For native
area
management
“Transfer efficiency” is key:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

8. Compare transfer efficiency between:
• Agricultural herbicide spray techniques
• Green Shoots technology:
• Foam herbicide
• Ultra-low-pressure spray

9. Agricultural
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

10. Agricultural Model
Uses
High Pressure Spray

11. As Pressure Increases
Drop Size Decreases
“A simple rule that holds for all nozzles.” Bete Fog Nozzle, Inc.

12. Well known: small drops are drift prone and reduce ability to
target.

13. Drift Studies
with Backpack
Sprayers – A
Few
• Snelder et al. (2008):
• 0.5 m from field boundary, drift was
12% of applied dosage
• 1.5-2.0 m from field boundary, drift
was 2%
• De Snoo et al. (1993):
• 0.6 m downwind from field, drift was
up to 10%
• 0.9 m downwind from field, drift was
up to 3%
• Thistle et al. (2017):
• 2 m downwind from swath, drift was
1%

14. Ideal study?
• One that accounts for the entire volume
released from a spray nozzle
• For example:
• 80% in the target area
• 20% beyond target area
• No study in the field comes close to that
yet.

15. This case study looks at how high pressure
affects spray coverage closer to the target area.
This is critical when doing spot spraying among
desirable species.

16. Theoretical spray coverage
D Spray angle
This illustration resembles ones
in technical guides for nozzles.
nozzle
Actual spray coverage

17. For agricultural spraying, there’s overlap of spray patterns.

18. White paper
Walking Direction
Spray
Coverage
Centerline
To explore spray
coverage, we did
indoor tests where we
sprayed colored water
onto white paper.

19. 10 in.
White Paper
The nozzle was held at a
constant height of 10 in.
Pressure was at 5 to 30
psi.
Measured this distance
Center
Line

20. Theoretical Spray Coverage Area for
Hypro VP-110-015
At 30 psi, many drops are deposited well beyond the
“theoretical spray coverage area.”
Center
Line

21. 14.0 in.
>35 in.
At 30 psi, the “shadow
spray coverage” extends
more than 35 in. from the
center line.
10 in.
Nozzle: Hypro VP-110-015.
?

22. Hypothesis: the spray pattern is
affected by the ground or other
objects.
Smaller lower velocity drops Smaller lower velocity drops

23. This big “shadow” spray coverage area may put
nearby desirable plants at risk.

24. You may think you
are avoiding the
desirable plant in
the middle.

25. Given the potential
for off-target harm. . .
Why does agriculture
prefer high pressure?

26. Why preferred for agriculture?
Generally, herbicide performance increases as
droplet size decreases at constant tank volume.
Knoche 1994.

27. Why might small
drops perform
better?

28. Agricultural
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

29. Small drops are
generally retained
better on leaves.
Yao et al. 2014.

30. Traditional
Agricultural
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

31. “300 μm diameter droplets had longer evaporation times
per droplet volume and greater wetted area per droplet
volume than the 600 μm diameter droplets.”
Xu et al. 2010.
300 μm Drops 600 μm Drop
Coverage area
+ wetted time
Volume

32. For transfer efficiency with
traditional agricultural
methods:
1. target just the weed.
2. Keep the herbicide on the
weed.
3. in the best form for
absorption.
Bad
Pretty
good

33. Green Shoots products use foam and spray
technology to increase “transfer efficiency.”

34. Precision Electronic
Dispenser for Foam
and Spray
Power Cap

35. Custom Backpack Frame

36. Ultra-low pressure
•Pressure range: 1.5 psi to 12 psi.
• Foam: 1.5 to 10 psi.
• Foliar spray: 5 to 12 psi.
• Basal spray: below 5 psi.
• Increments of 0.2 psi.

37. Power Cap
Lithium-ion
battery: highest
grade Panasonic®
cells provide all day
power.
Rugged Handle:
secure hold for
carrying and
opening tank.
Power Switch:
recessed to prevent
inadvertent
activation; blue
light indicates “on.”
Charging
Port: easy
access for
power cord.
www.greenshootsonline.com 37

38. Pressure Release:
brass knob for easy
grip.
No-Drip Shut-Off:
minimizes harm to
non-target organisms.
Anti-Kink Supports:
prevent hose kinking at
stress points.
Thick Wall High
Density Poly Tank:
Absorbs abuse.
Brass and
Stainless Steel:
Add strength at wear
points.
Nozzle: compatible with best
nozzle tips from Hypro® Lechler®
and TeeJet®.
Other Features
38

39. Manual Foam
Herbicide
Dispensers

40. Foam
Herbicide
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

41. 12 days later.
First, you can target just the weed with
a low-volume-high-concentration
application.

42. Low-volume-high-concentration applications:
• Low carrier volume
• High concentration of herbicide (typically
above 2% a.i.)

43. Application to toadflax.

45. Application to cut-stem of thistle

46. Dead Canada thistle – early July application at
Friends of Mississippi site.

47. Foam herbicide applied to a cut tree stem.

48. Electronic Dispenser with mesh brush attachment

50. Mesh brush with Large Handheld Dispenser

51. Stump applications using Electronic
Dispenser and mesh brush

52. Foam herbicide applied to notches.

53. Effective

54. Large
Foam
Herbicide
Dispenser
with foliar
nozzle.

55. Minnesota Dept Agriculture -
application to Japanese knotweed.

56. Even this
foliar
application
can be quite
precise.

57. Foam
Herbicide
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

58. Foam can really keep herbicide on the weed.

59. Phragmites Application

60. Foam slides
down grassy
stems.

61. Foam
Herbicide
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

62. Minimal coverage, but application is very effective.

63. Even a tiny amount of glyphosate can do the job even
though coverage is limited.

64. How can this be in light of Knoche?
• Glyphosate is different. Low-volume-high-concentration applications have
been found more effective. Cranmer et al. 1991; Feng et al. 1994.
• Other low-volume-high-concentration application methods have been found
highly effective using a variety of herbicides.
• Drizzle technique:
• DiTomaso 2016 (“drizzle” technique using concentrated triclopyr ester and surfactant).
• Motooka et al. 2002 (Hawaii weed control guide including “drizzle” technique)
• Splatter technique:
• Brooks et al. 2014(aminopyralid/fluroxypyr, fluroxypyr and metsulfuron-methyl
• to Siam weed).
• Herbicide Wiping:
• Harrington et al. 2016. (“Despite huge potential . . . only limited research.”)
• Surfactants: Surfactants can improve results, potentially even for herbicides
other than glyphosate as DiTomaso suggests.

65. For transfer efficiency using
foam herbicide:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.
Improve
At least
maintain

66. What about a spray
application system?

67. Ultra-Low-
Pressure Spray
Technology

68. Ultra Low-
Pressure
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

69. 10 psi
30 psi
14 in.
18 in.
14 in.
>35 in.
Smaller shadow spray
coverage area mean less
off-target spray.

70. 9 psi 30 psi
Bigger drops mean less drift.

71. 71
Ultra-Low Pressure :
3 psi
With basal bark applications, you will get a consistent
narrow stream at ultra-low pressure!

72. A lot of this applied herbicide is going to waste because of high pressure. Low
pressure can reduce this waste.
In calibrating our PED, we spray around 3-5 gallons per acre vs. 10-15 common with
pump backpacks.
Herbicide Waste

73. Ultra Low-
Pressure
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

74. First, reducing the velocity of drops
improves retention. Yao et al. 2014.
Lower pressure
creates lower
velocity drops

75. Second, surfactants will help larger
drops stick better to leaves.

76. Instead of bouncing off the leaf
. . .

77. The drop sticks with added
surfactant.

78. A 306 micron drop bounced off a leaf more than
50% of the time when pure water was used and
bounced 0% when a surfactant concentration of
0.75% was used.
Dong et al. 2015.

79. Ultra Low-
Pressure
Spray
Technology
“Transfer efficiency”:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.

80. 30 psi – Glyphosate 4% ai; no surfactant;
Hypro® 30HCX8 nozzle tip
5 psi – Glyphosate 4% ai; no surfactant;
Hypro® 30HCX8 nozzle tip
Given how glyphosate performs, the application at left
might perform better than the one at right.

81. But . . . let’s assume you want better coverage than
this.

82. Coverage can be adjusted to the desired
level using surfactants.

83. No surfactant.
5 psi 10 psi 30 psi

84. With Surfactant –
0.5% a.i. alkyl
polyglucoside (no
anti-foam)
5 psi
10 psi
30 psi

85. 85
10 PSI 30 PSI
www.greenshootsonline.com

86. For transfer efficiency using
ultra-low-pressure spray:
1. target just the weed.
2. Keep the herbicide on
the weed.
3. in the best form for
absorption.
Improve
At least
maintain

87. John Lampe:
•Email: john@greenshootsonline.com
•Cellphone: 651-245-4682
•Website: www.greenshootsonline.com