Dear Chris, Thank you for reaching out to the oregoninvasiveshotline.

Sorry to hear about your knotweed infestation. Unfortunately cutting knotweed is usually not enough. Cutting it can actually cause the plant to re-sprout more vigorously, and then begin to spread even more, as the cutting stimulates a stress response in the plant.

The most effective control of knotweed usually involves an integrated response that combines manual, cultural, and chemical methods.

Covering it with thick cardboard that extends 5-10 ft beyond the original patch for multiple years can be effective. Once you remove the cover you need to continue to monitor for many years, and perhaps replace the covering if it comes back. You can also try digging it up, but again, it is important to keep monitoring the site for many years until you are sure it is gone.

Of course dispose of the plant material in the trash and be careful to contain all the fragments, as knotweed spreads primarily vegetatively. Finally, attached to the report is a good article on how to control knoweed. I hope this helps!

Tania Siemens (she/her/hers)
Research Coordinator
Don't Pack a Pest for Academic Travelers
Oregon Sea Grant
Oregon State University
cell: 541-914-0701 email: tania.siemens@oregonstate.edu
https://seagrant.oregonstate.edu/outreach-and-engagement/invasive-species/dont-pack-a-past-student-travelers

Tania Siemens
June 29, 2020, 8:58 a.m.