Japanese knotweed is invasive

Q. What are these strange weeds? They are tall, hollow like bamboo, have large leaves and are taking over!

Judy from Austintown and others from Poland

A. Japanese knotweed. I’ve seen large patches of this all over Mahoning County. It is especially prevalent along railroad tracks and some roadways in the area. When I was in Marietta, you could see this invasive species cover the banks of the Ohio and Muskingum rivers on long stretches of bank. Thus, you’ll tend to see happy populations of it along creeks and even ponds.

It’s yet another invasive plant that is taking over many areas here in the Valley. It can form large colonies very quickly because it spreads by underground rhizomes. It was brought here as an ornamental plant and spread from there — another reason to know what you are planting to be sure you’re not contributing to invasive plant problems in our area.

Similar to Canada thistle, small pieces of the root of this plant can easily start a new plant. The link below gives details from our friends at Purdue Extension about how quickly this plant can spread and how the rhizomes can “extend 30 feet from the parent plant.”

The plant is hollow (thus, why my friends from Poland suggested it was like short bamboo). It can grow well over 6 feet tall.

Controlling this weed is extremely challenging. Also similar to Canada thistle, cutting it will only cause it to regrow with more stems. Cutting it over and over again and again will cause the roots to be depleted of energy, killing them. This could take years. A cut-stump application of a product containing glyphosate can be effective. These and other control options are reviewed in detail on the fact-sheet link below. If you use chemicals (organic or conventional), be sure to read and follow all label directions.

For photos and more about this plant: http://go.osu.edu/knotweed.

Eric Barrett is OSU Ext. educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 from 9 a.m. to noon Mondays and Thursdays to submit your questions.

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