1. A growing problem in the Cowichan Valley
Invasive Knotweeds:
A growing problem in the Cowichan Valley
Japanese knotweed
Polygonum cuspidatum

2. Cowichan River could be taken over

3. Probability of success
Biological Invasions
Biological Potential
Explosive
Cost
Probability of success
Area Infested
Introduction
Time

4. Spreads with tiny fragments of stem or root
Easily spread by river
Japanese knotweed
Polygonum cuspidatum

5. These plants came in with a small construction project
Japanese knotweed
Polygonum cuspidatum

6. Movement of soil can spread plants
Japanese knotweed
Polygonum cuspidatum

7. Battle between invasives – the knotweed will win…
Polygonum cuspidatum
Japanese knotweed
Himalayan blackberry
Rubus discolor

8. Three species and one hybrid
Japanese Knotweed
Japanese knotweed
Polygonum cuspidatum

9. Giant Knotweed
Polygonum sachalinense
Giant knotweed

10. Giant – as the name implies.
Giant knotweed
Polygonum sachalinense

11. Himalayan Knotweed
Polygonum polystachyum
Himalayan knotweed

12. Hybrid between Japanese and Giant Knotweeds
Polygonum x bohemica
Bohemian knotweed

13. Sandy River, Oregon

14. Sandy River, Oregon

15. Sandy River, Oregon

16. Salt water treatment on Haida Gwaii

17. Traditional treatments have involved herbicides (e. g
Traditional treatments have involved herbicides (e.g. Round-up = Glyphosate)

18. From Coastal Invasive Species Committee:
The most effective way to win the knotweed battle is to use specially-selected herbicide.
A product that can attack knotweed’s extensive root system is required.
Call a company with certified applicators. They can help you choose the appropriate treatment method for your property and get the job done safely.
There is no silver bullet with knotweed. Knotweed can take a few years of treatments to achieve control.
Be patient and committed to your treatment program and you can defeat this stubborn alien and protect your home.

19. An Ecologically Friendly Way of Treating Knotweed

20. Attack the plant at its weakest point
Plant Energy Reserves
May winter kill
Repeated cutting
J F M A M J J A S O N D
Months
Repeated cutting will kill the plant.

21. Initial cutting, May 21, 2011, Duncan

22. Initial cutting, May 21, 2011, Duncan

23. Cutting, June 11, 2011, Duncan

24. Cutting, June 11, 2011, Duncan

25. Cutting, July 7, 2011, Duncan

26. Cutting, July 7, 2011, Duncan

27. Knotweed gone – November 17. 2015

28. 2015 Koksilah Trials

29. Before Initial Cutting Treatment,
June 25, 2015

30. After Initial Cutting Treatment,
June 25, 2015

31. Before Second Cutting Treatment,
July 8, 2015

32. After Second Cutting Treatment,
July 8, 2015

33. Before Third Cutting Treatment,
July 24, 2015

34. After Third Cutting Treatment,
July 24, 2015

35. Before Fourth Cutting Treatment,
August 7, 2015

36. After Fourth Cutting Treatment,
August 7, 2015

37. Before Fifth Cutting Treatment,
August 27, 2015

38. After Fifth Cutting Treatment,
August 27, 2015

39. Before Sixth Cutting Treatment,
September 11, 2015

40. After Sixth Cutting Treatment,
September 11, 2015

41. Before Seventh Cutting Treatment,
September 28, 2015

42. After Seventh Cutting Treatment,
September 28, 2015

43. Before Eighth Cutting Treatment,
October 14, 2015

44. After Eighth Cutting Treatment,
October 14, 2015

45. End of the season,
Thanks Dave Lindsay!
October 14, 2015

46. Gravel bar site, June 25, 2015

47. After cutting, June 25, 2015

48. Decomposition of biomass

49. July 15, 2015, before

50. July 15, 2015, after

51. August 13, 2015, before

52. August 13, 2015, after

53. August 24, 2015, before

54. August 24, 2015, before

55. August 24, 2015, after

56. September 25, 2015, before

57. September 25, 2015, before

58. September 25, 2015, after

59. October 9, 2015, end of season, Thanks Cheri Ayers

60. In Summery:
Cutting does work (will monitor in the spring);
Cut materials can dry and die in the summer sun in location;
Watch out for runners trying to escape;
Need a large scale operational trial; and
Need to secure funding.

61. Strategy to Remove Knotweed from the Cowichan River Corridor
Hire 3 or 4 third year biology students
Starting May 15th, map all locations of knotweed along the river
Starting June 15th, cut all knotweed sites
Continue cutting every 2 weeks until October.
Repeat this process with 2 students the following year