The Dreaded Knotweed

Asked June 23, 2017, 2:52 PM EDT

We have a small yard, and this year Japanese Knotweed has emerged around the edge. It is only about 15 stalks but they are 5' tall and aggressive. I've read that herbicide may be the best way to treat them. If so, can you recommend one that is least harmful to the surrounding plants and pollinators. Also, is it best to wait until fall? Do you ever recommend digging them up? Thanks! Lindsay

Multnomah County Oregon

1 Response

Thank you for your question about control/eradication of knotweed. Here's a link to a comprehensive article about identification and control of this invasive weed. As you can see on page 3, under "Management," cutting, digging or pulling will only make things worse. Chemical controls (glyphosate and imazapyr) that have proven to have some success are listed on page 4. As you suspected, application between August and October is preferred, and re-treatment may be required before or during flowering and before leaf drop in subsequent years.

Hope this is helpful. Good luck!