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Japanese Knotweed

Polygonum cuspidatum Sieb. & Zucc.
Japanese Knotweed Japanese Knotweed
Jack Ranney, University of Tennessee

 

Commodities Affected:
Forestry and Natural Areas

 

Threat:

Japanese knotweed was probably introduced into the United States in the late 1800's. It was first planted as an ornamental and has also been used for erosion control and landscape screening. It can tolerate a variety of adverse conditions, including deep shade, high temperatures, high salinity and drought. Japanese knotweed is commonly found near water sources, such as along streams and rivers, in low-lying areas, waste places and utility rights-of-way and around old home sites. It spreads quickly to form dense thickets that exclude native vegetation and greatly alter natural ecosystems and is extremely difficult to control once established. Japanese knotweed poses a significant threat to riparian areas, where it can survive severe floods and rapidly colonize scoured shores and islands. Once established, populations are extremely persistent. Note – do not buy, sell, or plant Japanese knotweed.

 

Distribution:

In 100 Years of Change in the Distribution of Common Indiana Weeds by William and Edith Overlease (2002) reported that Japanese knotweed was not recorded in Indiana in 1899 (Coulter’s Catalogue of Indiana Plants) and in 1940 (Deam’s Flora).  In 2002, Overlease recorded Japanese knotweed in the following 77 counties: Allen, Bartholomew, Benton, Boone, Brown, Clark, Clay, Clinton, Crawford, Daviess, Dearborn, Decatur, DeKalb, Delaware, Dubois, Elkhart, Fayette, Floyd, Fountain, Fulton, Gibson, Grant, Greene, Hamilton, Hancock, Harrison,  Hendricks, Henry, Howard, Huntington, Jackson, Jasper, Jay, Jefferson, Johnson, Knox, Kosciusko, LaGrange, Lake, La Porte, Lawrence, Madison, Marion, Marshall, Martin, Monroe, Morgan, Noble, Ohio, Orange, Owen, Parke, Perry, Pike, Porter, Posey, Pulaski, Putnam, Randolph, Ripley, Rush, St. Joseph, Scott, Shelby, Spencer, Steuben, Sullivan, Switzerland, Tippecanoe, Union, Vanderburgh, Vermillion, Vigo, Warrick, Washington, Wayne, and Whitely.  Overlease reported that Japanese knotweed becomes very abundant, locally forming thickets.