Weed of the Week: Japanese Knotweed

The Eagle is partnering with the Wahkiakum Noxious Weed Control board to bring you this message.

Japanese Knotweed, as its name implies, is native to Asia. It is a Class B weed that is not known to be toxic and is a very aggressive escaped ornamental that can form dense stands, crowding out all other vegetation and degrading wildlife habitat. Japanese Knotweed can also create a fire hazard in the dormant season. It is difficult to control once established. This weed is a perennial species with spreading rhizomes and numerous reddish brown, freely branched stems. Plants can reach 4 to 8 feet in height and are often shrubby. The whitish to whitish-green flowers are in drooping clusters from leaf axils. This is often found in waste places, gardens, roadsides, streams and riverbanks.

Japanese Knotweed is on the Washington State quarantine list, which means it is prohibited to transport, buy, sell, offer for sale, or distribute these plants into or within the state of Washington. This also applies to the sale or distribution of seed packets, flower seed blends, or wildflower mixes of quarantined species into or within the state of Washington. Please see WAC 16-752 for more information on the quarantine list.

Knotweed species resemble each other. Japanese Knotweed is shorter than Bohemian Knotweed or Giant Knotweed. If you have questions about Japanese Knotweed or other noxious weeds and their identification and control, contact Andy Lea at 360-795-3852.