Japanese Knotweed

Asked September 20, 2018, 3:36 PM EDT

I am trying to eradicate the Japanese Knotweed from my yard in South Minnespolis. It’s very established; it was in my yard when I bought my house 30 years ago and FINALLY, about a year ago, someone was able to identify it. Since then I’ve been cutting the cane about 1” from the ground and immediately dabbing it with Stump-out, Stump and Vine Killer (with triclopyr); I put food coloring in it so I can see that the cut part been treated. Is this an effective treatment?

I’ve been putting the waste in plastic bags and then into the garbage that’s heading to the incinerator. However, I was told by the city solid waste department that it has to go in with yard waste. I understand that large scale composting gets much hotter than home composting, will this kill the rhizomes, or could I effectively compost it myself in heavy black plastic bags with other yard waste? I don’t want to be responsible for allowing it to spread.

Hennepin County Minnesota

1 Response

Greetings! Thank you for contacting AaE for help.

This is a knotty problem, indeed (no pun intended as you'll see when you read on). The cut stems, if placed in contact with soil, can sprout new plants so destruction is important. The MIchigan DNR recommends placing the cut material into black plastic bags to be sent to a facility for incineration. And since your waste collector has said not to do that, you'll need to consider other options. If your community's burning ordinance permits, you could thoroughly dry the plant material on a non-soil surface then incinerate it on your property. It doesn't burn well if fresh. Another option is to compost it if the temperature of the compost can be maintained above 55 degrees centigrade (131 degrees F) for at least three consecutive days. So if you're able to compost at those temps, you could try that.

I would contact your community and the Minnesota DNR to see if something can be worked out to help homeowners with this type of plant material so that it is not inadvertently spread.

Incidentally, the following link to the Michigan DNR PDF on Japanese knotweed (where I obtained most of my information) contains more information on destruction of this plant including effective chemicals that can be used to destroy the underground rhizomes.

I'm also including a link to the NRCS MN797 job sheet on Japanese knotweed where you'll see some control information that may conflict with Michigan. You sound like a very conscientious citizen and I'm sure you'll find a way to eliminate this plant from your property. https://efotg.sc.egov.usda.gov/references/public/MN/797JapaneseKnotweed.pdf

Because I mention chemical control, I need to let you know that by law all chemical applications must follow the instructions provided on the label of the product used in order for the product to be effective and safe for you and the environment.

Best of luck!