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submitted by Jana Rapetti & Tony Telck
Japanese Knotweed

Japanese Knotweed (Polygonum cuspidatum)--a member of the Polygonaceae family--is an herbaceous, rhizomatous perennial that can grow over twelve feet tall. The leaves are thick and leathery, about four to five inches long bearing few hairs, and are square across the base with an abruptly tapered tip. Japanese knotweed habitat includes riparian areas, flood plains, forest edges, meadows, rights-of-way and parks. Japanese knotweed is listed as a noxious weed in four western states including California, Oregon, Washington, and Colorado. In Colorado, it is an A-list weed mandated for eradication.                                          

In Canon City, Colorado, Japanese knotweed occurs in four isolated locations. It appears to favor wet areas along ditch-banks.  For the past several years, Fremont County Weed Management (FCWM) has been controlling the infestations with an aquatic-approved chemical (Rodeo) and surfactant. So as to not contaminate irrigation waters, FCWM staff have been bending the shoots away from the ditch, to ensure the chemical remains on the uplands when spraying.  Treatments have been highly successful to-date!  

The most established infestation has proven a bit more challenging.  In this location, FCWM has been more successful with a mechanical and chemical method.The tall stalks were cut with a blade on a weed-eater and fresh-cut stems were treated with a concentrate of the same chemical. The cut shoots were burned to prevent re-rooting.  This year, the plant has remained low to the ground and has not been flowering, due to the stress of previous treatments on the plant.   

Jana Repetti is the Fremont County weed management director.

Japanese Knotweed Fact Sheet
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