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 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 WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
CONTACTS
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
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.
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.
The Nature Conservancy. Japanese
Knotweed: Element Stewardship Abstract. In: Wildland Weeds Management & Research
Program, Weeds on the Web.
Plant Conservation
Alliance, Alien Plant Working Group.
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