Japanese Knotweed a Problem in Europe and North America


Image from en.wikipedia.org

Image from en.wikipedia.org

Fallopia japonica, or Japanese knotweed, has a long, slender stem and a hollow middle. Young stems are edible if somewhat bitter in taste. The leaves are oval shaped and in late summer or fall, the knotweed may have small white flowers. Beekeepers value Japanese knotweed because it is an important source of nectar that creates delicious honey. At a passing glance, Japanese knotweed could be mistaken for bamboo however the similarities end with their appearances.

Japanese knotweed is native to Japan, China, Korea, and other Eastern Asian countries. Upon its introduction to Western Europe and North America, the plant spread voraciously and it now labeled as one of the top 100 worst invasive species. Japanese knotweed is present in over half of the United State’s fifty states, and is considered an invasive weed in ten states including Ohio, Alaska, Pennsylvania, Oregon, Washington, and New York.

Not only is the knotweed hardy and quick to spread, it is notoriously difficult to control and remove. Japanese knotweed is dependent on its underground root structure and stem structure rather than seeds. These roots, called rhizomes, allow the plant to spread and survive even if the leafy parts of the plants are cut off. Dormant rhizomes can survive for years and still be able to send up shoots.

There are several ways to control and remove Japanese knotweed. One way is to repeatedly cut back the stems until the plant loses its vigor and then it is easier to remove both stems and roots. However, this method could take years and the knotweed may just continue to spread. There are many herbicides that are effective against Japanese knotweed, but they have to be applied at a specific time of year and usually after the plant has been cut black. Since the key to the knotweed’s survival is its roots, the herbicide must penetrate the entire plant and then it must all be removed. Even with an herbicide treatment, Japanese knotweed may still grow back in the treated area for several years and will require continual treatment.

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