Polygonum cuspidatum Siebold & Zucc. (Family: Polygonaceae)

Also known as: crimson beauty, Mexican bamboo, Japanese fleece flower, Reynoutria

Description: Japanese knotweed is a shrublike, herbaceous perennial which can grow to over 10 feet tall and has alternate, ovate, abruptly pointed leaves about 4 to 6 inches long and 3 to 4 inches wide. Its stems are smooth and swollen at the joints where the leaf stems attach. Stems are often reddish at these joints, if not along the entire length, and tend to have a zig-zag appearance. Tiny, whitish flowers occur in August and September in branching sprays. Tiny, brown, triangular fruits follow in September and October.

Habitat description: This fast growing, perennial forbe can be found sporadically through the county. It is occasionally seen planted in yards. The few large colonies present in the county are found along water drainages. Rarely producing viable seed in Indiana, it spreads vegetatively as root stock is broken off and transported during flood events or disturbance activities. Until recently, the largest colony was located on the South side of SR 46 in a drainage ditch, just East of the Little Nashville Opry site.This fast growing, perennial forbe can be found sporadically through the county. It is occasionally seen planted in yards. The few large colonies present in the county are found along water drainages. Rarely producing viable seed in Indiana, it spreads vegetatively as root stock is broken off and transported during flood events or disturbance activities. Until recently, the largest colony was located on the South side of SR 46 in a drainage ditch, just East of the Little Nashville Opry site.

Origin: Native to eastern Asia, this plant was probably introduced to the United States in the late 1800s. It was first used as an ornamental but was also planted for erosion control and landscape screening. It is currently found throughout the eastern U. S., in several western states, and in Alaska, which, to date, has few exotic invasive plants.

Distribution: Japanese knotweed can tolerate a variety of adverse conditions including full shade, drought, high temperatures, and high salinity. It is commonly found along streams and in low-lying areas, along roadsides and utility right-of-ways, around old home sites, and in waste places.

Problem: Japanese knotweed spreads by both rhizomes and seeds, allowing it to colonize areas rapidly and making established populations quite persistent. Its dense growth shades and excludes native vegetation, greatly altering ecosystems and reducing wildlife habitat.

Control: Cutting or mowing Japanese knotweed will reduce rhizome reserves but must be done at least 3 times during the growing season. For chemical control, apply a 3% a.i. solution of glyphosate with a surfactant to populations in early fall.

USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations.

For more information, see http://www.invasive.org/species/weeds.cfm.

Photo credits:

• Britt Slattery, US Fish and Wildlife Service, Bugwood.org, Image Number: 1237059
• Theodore Webster, USDA Agricultural Research Service, Bugwood.org, Image Number: 1550181
• Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org, Image Number: 1550186
• Mark Folsom, Bugwood.org, Image Number: 1197030
• Jil M. Swearingen, USDI National Park Service, Bugwood.org, Image Number: UGA0581045
• David J. Moorhead, University of Georgia, Bugwood.org, Image Number: UGA5078027
• Randy Westbrooks, U. S. Geological Survey, Bugwood.org, Image Number: UGA5331055
• New York Invasive Species Information, nyis.info