We can easily kill this plant (I think), but we would like to know its Planet of Origin first. It really looks alien.

Reporter
April 23, 2011, 5:32 a.m.

Dear Lou,

Thanks so much for submitting a report and photos to the hotline. What you have is Japanese knotweed (or Fallopia japonica), which is a highly invasive plant that is very difficult to control due to it's underground rhizomes (which you have observed). It is known to push up through concrete, and destroy the foundations of houses. In grows in riparian areas, (stream sides), and in Oregon it has infested and permanently altered miles of stream side habitat by excluding important native species..

I would highly recommend you work to control the continued spread of this plant into your yard. The only permanent solution will be to work with your neighbor to control the patch they have in their yard. Otherwise you will forever be battling it spreading from the source patch. Controlling knotweed is a long-term commitment. With herbicides it will likely take 2-3 yrs of re-treatment, and manual control could take up to 10 yrs of repeated grubbing of the rhizomes until you find and get them all. Knotweed can re-grow from tiny fragments, so it is important to carefully dispose of all plant material in the garbage (NOT the compost).

I am sorry to bring you bad news! But, one bit of good news is that it looks like you caught your infestation early, which means it wont be as hard to control. When I confirm this report you will be able to access the report you submitted on line, and it will contain links to information on how to control it. Please feel free to contact me at the email below if you have any questions. Thanks again for your report!

Sincerely,
Tania

Tania Siemens
Invasive Species Early Detection and Rapid Response Coordinator
The Nature Conservancy
WISE Program Coordinator (Watershed and Invasive Species Education)
Oregon Sea Grant Extension
tania.siemens@oregonstate.edu
541-914-0701

Tania Siemens
April 29, 2011, 12:35 a.m.