Where does it grow?

Japanese Knotweed is found along streambanks, in moist waste places, neglected gardens, and roadsides.

What is the distribution in Washington State?

Click on map to enlarge.

• Japanese Knotweed is documented throughout Washington, refer to the map for distribution in specific counties.
• If you think you may have seen this weed, please contact your county weed coordinator or us at noxiousweeds@agr.wa.gov.

• Distribution map is based on 2003 data.

How do I control it?

General control methods: Mowing or cutting plant shoots is ineffective alone. However, mowing followed by herbicide treatments will provide some control. Methods must be repeated if infestation is very large. Care must be taken not to produce new plants, entire plant material should be removed, dried and burned if possible. New plants can sprout from very small fragments.

Cultural: Grubbing out small clumps when discovered can prevent new colonies from establishing:

• rhizomes and fragments left in the ground or nearby can regenerate and spread infestations
• entire root system must be removed, since resprouting can occur from rhizomes

Herbicide: Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.

Mechanical: Mowing or cutting plant shoots is ineffective alone:

• mowing may eventually tax the plant of it's resources
• mowing must be repeated throughout the growing season
• all material must be removed to prevent new infestations

Biological: None known.

Are there plants that may be confused with Japanese Knotweed?

Knotweed species resemble each other, Japanese Knotweed is much shorter than Bohemian or Giant Knotweed. If you need help with plant identification, please contact your county noxious weed coordinator.

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