Polygonum cuspidatum

History of Spread

Polygonum cuspidatum (Japanese Knotweed) is native to East Asia. It was widely planted as an ornamental in the late 1800s, and by 1894 was established around Schenectady NY, Atlantic Highlands NJ, and Philadelphia PA. This plant proved to be a rapid spreader and extremely difficult to eradicate (Patterson 1976). It is now known from 40 states, including AK, and is listed as an invasive weed in many states and Europe (Natural Resources Conservation Service 2001; Washington Department of Ecology 2001).

While Polygonum cuspidatum (Japanese Knotweed) is often regarded as an upland plant, it is often especially abundant and invasive in riparian zones (Washington Department of Ecology 2001). It has been reported from tidal freshwater marshes of the Merrimack River MA (Caldwell and Crow 1992).

In the Chesapeake Bay watershed, P. cuspidatum was first collected in from culture from the 'Botanic Garden' in 1875, and first reported growing in the wild at Glen Echo Junction MD in 1916 (U.S. National Herbarium collections). In 1946, it was still listed as a 'waif' in the Baltimore-Washington area (Hermann 1946), but is now widespread in MD and VA (Brown and Brown 1984; Harvill et al. 1992). There are no published records of this plant in tidal wetlands in the Chesapeake Bay. However, a large colony of P. cuspidatum occurs in the intertidal zone, at Havre de Grace, adjacent to a boardwalk along the uppermost shores of the Bay. Numerous plants were found along the edge of the upper intertidal along the Susquehanna River, in Susquehanna State Park, along the nontidal and upper tidal Gunpowder River, an upper Bay tributary in 1998-2002 (Fofonoff, personal observations). Dense growths of P. cuspidatum were also found in the upper edges of a brackish tidal marsh south of Chesapeake Beach MD. The degree of immersion of this latter population is unknown (Fofonoff, personal observations).

In Europe, a biocontrol agent, a psyllid insect (plant louse), Aphalara itadori, has been researched in the United Kingdom, and found to be highly specific in its feeding. Releases are beginning in 2011 in England and may begin in the northeast US and Canada in 2012 (Carpenter 2011). References- Brown and Brown 1984; Caldwell and Crow 1992; Carpenter 2011; Fofonoff, personal observations; Harvill et al. 1992; Hermann 1946; Patterson 1976; Natural Resources Conservation Service 2001; Washington Department of Ecology 2001

Invasion Comments