Japanese knotweed invades Hortonville
Village seeks reports from residents
By John Faucher
Village administrator Diane Wessel informed Hortonville Village Board members at its Aug. 18 meeting, that there have been four stands of Japanese knotweed discovered in the village.
Japanese knotweed is a non-native invasive plant first introduced from Asia as an ornamental plant. It can be found in 39 of 50 states in the U.S. including Wisconsin.
Japanese knotweed is listed by the World Conservation Union as one of the world’s worst invasive species. In Wisconsin, the plant is legally classified as restricted, under NR 40.
According to the Wisconsin Department of Natural Resources, Japanese knotweed is an herbaceous perennial that forms large dense colonies of erect arching stems that resemble bamboo. The plant can grow up to 10-feet tall and often will completely crowd out any other species of plants.
According to the DNR, the invasive plant poses a significant threat to riparian areas where it prevents streamside tree regeneration and increases soil erosion. The plant also disrupts nutrient cycling in the soil, and the plant itself contains chemicals that are toxic to surrounding vegetation.
“It not only poses an environmental threat by increasing erosion and decreasing biodiversity, but it can destroy foundations, pavement and pipes,” said Wessel.
According to the University of Wisconsin Extension, the plant often spreads by its roots, which can grow up to 6 feet deep and extend over 60 feet horizontally. It can also spread from seed or small cuttings that fall to the ground.
Wessel said that in Hortonville, the noxious weed ordinance requires that Japanese knotweed be destroyed when discovered.
“We are monitoring for additional locations and are getting the word out via social media,” said Wessel.
Documenting and reporting occurrences of Japanese knotweed will help prevent the spread of the species. According to the DNR, Japanese knotweed is easier to locate in August and September because the plants are typically in full bloom. The plants will exhibit clustered spikes of small cream-colored white or greenish flowers.
The leaves of the plant are simple, alternate, 3-4 inches wide, and 4-6 inches long. Leaves are spade-shaped.
Removal and disposal
Chemical treatment is effective for controlling standing growth colonies. According to the DNR, plants are more susceptible to herbicides if they are cut when 4-5 feet high and then chemically treated when the new growth reaches around 3 feet.
If hand pulling the weed, it is best to pull by the root crown. Remove as much of the rhizome as possible to new growth. Rhizomes remaining in the soil will produce new plants at each node. Persistent cutting or pulling on smaller growths of the plant may be effective, but will likely need to be repeated.
According to the UW-Extension, cut or mowed plants should be bagged and disposed of in a landfill, or burned, to prevent possible spreading or transporting the species to new areas.
For more information visit www.dnr.wi.gov.