Distribution

Japanese knotweed is currently found outside of cultivation in 36 states in the continental United States, including Montana. It is listed as a noxious weed or prohibited invasive species in Alabama, California, New Hampshire, Oregon, Vermont, and Washington. In Montana, the occurrence of Japanese knotweed has been verified by the Montana Department of Agriculture in 25 locations in 12 counties from 1961 through 2004. Montana counties having populations of Japanese knotweed at some point in time since 1961 include Hill, Ravalli, Yellowstone, Broadwater, Cascade, Missoula, Sanders, Flathead, Lincoln, Lake, Valley, and Lewis and Clark. In addition to these counties, Plant Materials staff has identified this species at five additional sites in Carbon, Yellowstone, and Flathead counties.

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Last Modified: 11/14/2007