This document is a presentation on methods for controlling invasive knotweed species. It discusses current chemical control methods like foliar spraying, stem injection, and cut stem treatments. It notes the disadvantages of these methods, like using large amounts of herbicide and causing off-target damage. The presentation explores ways to improve methods by reducing the quantity of herbicide used and minimizing off-target impacts. It describes experiments with injecting herbicides into knotweed rhizomes and bending stems to expose tissue before treatment. The goal is developing more effective and sustainable control techniques.

1. Injection of Herbicides into
Rhizomes of Knotweeds and Other
Invasive Species
Upper Midwest Invasive Species Conference
October 29-31
La Crosse, Wisconsin
John Lampe
Green Shoots, LLC
Saint Paul, Minnesota
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3. Knotweed – Why Control?
• It is listed by the World Conservation Union as
one of the world's 100 worst invasive species.
• This is not precise ranking but does show
recognition of how problematic species is.

4. Outline of Talk
• Background on Knotweed
• Current Chemical Control Methods
• How Can Our Methods be Improved to:
– Reduce quantity of herbicide used
– Reduce off-target harm

5. Common Species of Knotweed
• Japanese knotweed (Polygonum cuspidatum)
• Giant knotweed (Polygonum sachalinense)
• Bohemian knotweed (Polygonum x
bohemicum) – hybrid

6. Identification
Good source: Prather TS, Miller TW, Robins
SS, Knotweed shrubs: identification, biology, and
management, Pacific Northwest Extension
Publication 2009

7. Knotweed Colony

8. Knotweed Leaves
• Dark green leaves
• Un-toothed
• alternate
Photo Credit: Steve Manning, Invasive Plant Control, Bugwood.com

9. Knotweed Stems - Young

10. Knotweed Stem - Dry
• Hollow internodes
• Septum separating
• Up to 2 in. dia.
Photo Credit: James H. Miller, USDA Forest Service, Bugwood.com

11. Knotweed Rhizome
Rhizome

12. Knotweed Spreads by
• Rhizome extension – up to 6 to 8 feet a year
• Distribution of plant parts
– Rhizome pieces – as small as 0.7 g (Brock 1992)
– Node pieces
• Seeds – not major source in WA. (Miller 2005)

13. Knotweed Badness
• Riparian areas especially vulnerable
• Out-compete other plants => monoculture
– Loss of trees
– Changes in soil fertility
– Erosion along streambeds and stream banks

14. Knotweed Monoculture
Photo Credit: Justin Knabe, Minnesota DOT

15. Knotweed Rhizome Extension
Photo Credit: Popplewell Associates, York, UK

16. Knotweed Rhizome Extension

17. Knotweed Rhizome Extension

18. Non-Chemical Control
• Not practical except with small infestations
• Danger of vegetative spread
• See King County, Best Management Practices
(2008)

19. Chemical Control Methods
• Foliar
• Stem injection
• Cut stem

20. Key Herbicides
• Glyphosate – aquatic label
• Triclopyr – aquatic label; only foliar
• Imazapyr – aquatic label; only foliar

21. Knotweed Rhizome Tough to Kill!
Key Problem: older parts of rhizome and dormant
buds are weak sinks. (Bashtanova et al. 2009.)

22. Knotweed Rhizome – Tough to Kill!

23. Foliar
• Advantages
– Fastest application method
– Decent control: 81%. (Miller 2005)
• Disadvantages
– Off-target harm: Avg. injury: 68%. (Miller 2005)
– Hard to treat tall plants

24. Stem Injection

25. Stem Injection
• Use hypodermic or special injector
• Inject up to 5 ml into stem
• Between 1st and 2nd node above ground

26. Stem Injection
• Advantages
– Precision
– No stem disposal
– Efficacy; Avg control: 88% (Miller 2005)
• Disadvantages
– Time-consuming
– Id of treated stems
– Non-target injury: 26% (Miller 2005)

27. Biggest Disadvantage of Stem Injection
• Requires 5 ml of herbicide per aerial shoot
– Equivalent to frill application on 10 to 15 inch
woody stem. AquaMaster Label.
• Aerial shoot density averages about 9
stems/m2. Brock 2007.
• 45 ml of 54% a.i. glyphosate per square
meter.
• May explain 26% non-target injury found by
Miller.

28. Cut Stem
• Cut stem 5 to 10 inches off ground
• Immediately pour up to 3 ml into hollow of
stem

29. Pouring Herbicide into Cut Stem

30. Cut Stem
• Advantages
– Low cost equipment
– Control? (Miller did not test)
• Disadvantages
– Time-consuming
– Disposal of green aerial shoots
– Amount of herbicide used

31. Stem Wipe
• Inconsistent Results (Miller 2005)

32. Follow-Up Applications
• Washington State Dept Agriculture:
– Data show “significant decrease in knotweed
following six years of annual treatments.
– However, knotweed is still present at each
monitoring site.” (Statewide Knotweed Control
Program; 2010 Progress Report)

33. How Can Methods Be Improved?
• Reduce repeat applications
• Reduce quantity of herbicide used
• Reduce off-target harm

34. We Have Been
Trying Several Methods

35. Rhizome Injection

36. Rhizome and Roots

37. Rhizome Injection
Needle reaches to
below-ground
Internode

38. Herbicide Used
• AquaMaster – glyphosate; 54% a.i.
• Dose at 2ml
• Well below AquaMaster label rate for hollow
stem injections: 5 ml

39. Inserting Needle into Cut, Dead Stem

40. Injecting into Rhizome
through Cut Stem

41. Inserting Needle into Bent Live Stem

42. Results?

43. Ongoing Rhizome Injections
• Winter and early spring injections did not
produce results
• Late spring injections show promise
• Currently doing tests – late summer and Fall

44. Other New Methods Being Explored

45. Cut, Bend, and . . .

46. Treat with Foam Herbicide

47. Munch, Bend, and . . .

48. Treat with Foam

49. Tromp, Wait, and . .

50. Treat Regrowth with Foliar Applied

51. Low Volume Foam Herbicide

52. Bend and Immediately Treat . . .

53. Stems and . . .

54. Foliage

55. Potential Advantages of Foliar
Methods
• Not treating tall plants – reduces off-target
harm
• Treating with Foam Herbicide
– Improves adhesion
– Reduces drift
• Late season – should improve treatment
success

56. Rhizome Injection Methods
• Less time consuming
• Less herbicide
• Injecting into rhizome – will this improve
treatment success?

57. Bent Stem Wiping Methods
• Exposing vascular tissue
• Foam herbicide sticks to stem
• Uses a lot less herbicide

58. Green Shoots
John Lampe – contact:
• john@greenshootsonline.com
• 651-245-4682 (cell)
Website:
www.greenshootsonline.com
• Email or call for copy of
presentation
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