Japanese Knotweed – Invasive Plant That Is Virtually Unstoppable

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This plant thrives on any disturbance whether natural or manmade and can cause the following damage:

• Can grow right through tarmacs and drive ways.

• Can grow out of walls and up into homes.

• Can overtake fields including parks & recreational areas.

• Can overrun & damage archeological sites and graveyards.

• Can cost a lot of money to repair damage as well as the cost of trying to control.

• Many others…

Japanese Knotweed was introduced from Asia to Europe in the mid-19th century and to the United States in the early 20th century. It is native to Japan, Northern China, Taiwan and Korea. This plant is so invasive that its distribution now covers much of mainland Europe and is in the process of doing so in Canada and the United States as well.

Japanese Knotweed   Invasive Plant That Is Virtually Unstoppable

There are a lot of unusual facts regarding Japanese Knotweed. It is a herb that in Japan is called “itadori” which means… “heal’s the sick”. Japanese Knotweed has a lot of other common names including:

• Japanese Bamboo

• Mexican Bamboo

• Japanese Fleece-Flower

• Hancock’s Curse

• Wild Rhubarb

• Gypsy Rhubarb

• Sally Rhubarb

• And others…

Another interesting fact is that Japanese Knotweed is a dioecious plant. This means that you need both male and a female plants for sexual reproduction to take place. What’s amazing is that the invasion in Europe and the United States is by a single sex version (female only) and it’s a clone of itself. This means it can only spread through vegetative reproduction. In other words, it is spreading by cuttings, or from pieces of the rhizome dispersed by nature or humans.


How do you control this plant? It’s not easy especially since the extensive underground rhizome system sustains the plant even when its top growth is removed. Physical removal alone won’t do it. It’s got to include a chemical treatment that goes after the rhizomes. That’s where the challenge is however. You have to be concerned with the surrounding area, plants and people. Included in this are waterway runoffs, local farms or gardens, and animals.

Japanese Knotweed will require a number of herbicide treatments over several years before it is completely eradicated. For shorter term control you can just cut the plants down but this can be a double edged sword. Since Japanese Knotweed regenerates vegetatively the small rhizome fragments can produce even more viable roots and shoots.

Biological Controls: Japanese Knotweed has some natural enemies in Asia but not in new environments like Europe or the United States and Canada. Introducing insects and other natural enemies of Japanese Knotweed is taking a gamble because these in turn may get out of control and cause unforeseen havoc. In the future we may see natural biological controls introduced as they are proven out for effectiveness and safety.

Note: If you are engaged in an effort to get rid of or control Japanese Knotweed please start by contacting your local County Extension Agent or Master Gardener. They will advise you on the methods accepted and working in your particular region.