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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

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FACT SHEET: JAPANESE KNOTWEED

Japanese Knotweed 

Fallopia japonica 

Buckwheat family (Polygonaceae) 

NATIVE RANGE 

Eastern Asia 

DESCRIPTION 

Japanese knotweed is an upright, shrublike, herbaceous perennial that can 

grow to over 10 feet in height. As with all members of this family, the base of 

the stem above each joint is surrounded by a membranous sheath. Stems of 

Japanese knotweed are smooth, stout and swollen at joints where the leaf 

meets the stem. Although leaf size may vary, they are normally about 6 inches long by 3 to 4 inches wide, broadly oval to 

somewhat triangular and pointed at the tip. The minute greenish-white flowers occur in attractive, branched sprays in 

summer and are followed soon after by small winged fruits. Seeds are triangular, shiny, and very small, about 1/10 inch 

long. 

Japanese knotweed is designated a noxious weed in the State of Washington. 

ECOLOGICAL THREAT 

Japanese knotweed spreads quickly to form dense thickets that exclude native vegetation and greatly alter natural 

ecosystems. It poses a significant threat to riparian areas, where it can survive severe floods and is able to rapidly 

colonize scoured shores and islands. Once established, populations are extremely persistent. 

DISTRIBUTION IN THE UNITED STATES 

Current distribution of Japanese knotweed includes 36 states in the lower 48 

from Maine to Wisconsin south to Louisiana, and scattered midwest and 

western states. It is not currently known to occur in Hawaii. 

HABITAT IN THE UNITED STATES 

Japanese knotweed can tolerate a variety of adverse conditions including full 

shade, high temperatures, high salinity, and drought. It is found near water 

sources, such as along streams and rivers, in low-lying areas, waste places, 

utility rights-of-way, and around old homesites. It can quickly become an 

invasive pest in natural areas after escaping from cultivated gardens. 

BACKGROUND 

Japanese knotweed was probably introduced to the U.S. in the late 1800's. Also known as crimson beauty, Mexican 

bamboo, Japanese fleece flower, or Reynoutria, it was first introduced as an ornamental and has also been used for 

erosion control and for landscape screening. It is now found throughout the eastern U.S., in several western states, and 

Alaska, which has few exotic invasive plants to date. 

BIOLOGY & SPREAD 

Japanese knotweed spreads primarily by vegetative means with the help of its long, stout rhizomes. It is often transported 

to new sites as a contaminant in filldirt seeds, sometimes distributed by water, and carried to a lesser extent by the wind. 

Escapees from neglected gardens, and discarded cuttings are common routes of dispersal from urban areas. 

MANAGEMENT OPTIONS 

Grubbing is effective for small initial populations or environmentally sensitive areas where herbicides cannot be used. 

Using a pulaski or similar digging tool, remove the entire plant including all roots and runners. Juvenile plants can be hand 

pulled depending on soil conditions and root development. Any portions of the root system not removed will potentially 
20 May 2005 Page 2 of 3 

Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

resprout. All plant parts (including mature fruit) should be bagged and disposed of in a trash dumpster to prevent 

reestablishment. 

Chemical 

Cut stem application

Use this method in areas where plants are established within or around non-target 

plants or where vines have grown into the canopy. This treatment remains effective 

at low temperatures as long as the ground is not frozen. Cut the stem about 2 

inches above ground level. Immediately apply a 25% solution of glyphosate (e.g., 

Roundup®, or use Rodeo® if applying in or near wetland areas) or triclopyr (e.g., 

Garlon®) and water to the cross-section of the stem. A subsequent foliar 

application of glyphosate may be require to control new seedlings and resprouts. 

Foliar application 

Use this method to control large populations. It may be necessary to precede foliar 

applications with stump treatments to reduce the risk of damaging non-target 

species. Apply a 2% solution of glyphosate or triclopyr and water to thoroughly wet all foliage. Do not apply so heavily that 

herbicide will drip off leaves. A 0.5% non-ionic surfactant is recommended in order to penetrate the leaf cuticle, and 

ambient air temperature should be above 65 oF. 

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. 

NOTICE: mention of pesticide products on this page does not constitute endorsement of any material.

CONTACT 

For more information on the management of Japanese knotweed, please contact: 

• Kris Johnson, Great Smoky Mountains National Park, Gatlinburg, TN 

• Japanese Knotweed Alliance, http://www.cabi-bioscience.org/html/japanese_knotweed_alliance.htm 

• Robert J. Richardson, Aquatic and Noncropland Weed Management, Crop Science Department, Box 7620, North 

Carolina State University, Raleigh, NC 27695-7620, (919) 515-5653, Rob_Richardson at ncsu.edu 

SUGGESTED ALTERNATIVE PLANTS 

Many attractive native herbs and shrubs are available that make excellent alternatives to Japanese knotweed. Contact the 

native plant society in your state for more information. 

OTHER LINKS 

• http://www.invasive.org/search/action.cfm?q=Polygonum%20cuspidatum 

• http://nbii-nin.ciesin.columbia.edu/ipane/icat/browse.do?specieId=86

AUTHOR 

Tom Remaley, Great Smoky Mountains National Park, Gatlinburg, TN 

EDITOR

Jil M. Swearingen, National Park Service, Washington, DC 

PHOTOGRAPHS 

Tom Remaley, Great Smoky Mountains National Park, Gatlinburg, TN 

Jil M. Swearingen, National Park Service, Washington, DC 

REFERENCES 

Ahrens, J.F. 1975. Preliminary results with glyphosate for control of Polygonum cuspidatum Proceedings of the Northeast 

Weed Control Conference 29:326. 
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

Child, L.E., L.C. De Wall, P.M Wade, J.P. Palmer. 1992. Control and management of Reynoutria species (knotweed). 

Aspects of Applied Biology 29:295-307. 

Figueroa, P.F. 1989. Japanese knotweed herbicide screening trial applied as a roadside spray. Proceedings of the 

Western Society of Weed Science 42:288-298. 

Hirose, T., K. Kitajima. 1986. Nitrogen uptake and plant growth. I. Effect of nitrogen removal on growth of Polygonum 

cuspidatum Ann. Bot. 58(4):479-486. 

Japanese Knotweed Alliance 

Jennings, V.M, R.S. Fawcett. 1977. Weed control: Japanese polygonum (Polygonum cuspidatum Sieb. and Zuce.). PM 

Iowa State Univ. Science Technol. Ames. Coop. Ext. Serv. 762, 2. 

Pridham, A.M.S., A. Bing. 1975. Japanese bamboo (Polygonum cuspidatum, Polygonum sachalinens). Plants Garden 

31(2):56-57. 

Radford, A. E., H.E. Ahles, C.R. Bell. 1968. Manual of vascular flora of the Carolinas. Chapel Hill, NC: The University of 

North Carolina Press, 1183. 

Randall, J.R. and J. Marinelli. 1998. Invasive Plants: Weeds of the Global Garden. Brooklyn Botanic Garden, Handbook 

No. 149, p. 77. 

Scott, R., R.H. Marrs. 1984. Impact of Japanese knotweed and methods of control. Aspects of Applied Biology 291-296. 

Smith, R.C. 1990. Polygonum cuspidatum var. compactum American Nurseryman 172(2):142. 

Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Japanese Knotweed 

(Polygonum cuspidatum). http://www.invasive.org/weedus/subject.html?sub=3414. 

The Nature Conservancy. Japanese Knotweed: Element Stewardship Abstract. In: Wildland Weeds Management & 

Research Program, Weeds on the Web. 

USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 

70874-4490 USA.