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
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.