Japanese Knotweed (Fallopia Japanica)

Japanese Knotweed (Fallopia Japanica)
Introduced to the United States from Eastern Asia in the late 1800s, Japanese knotweed has
since acquired a nasty reputation as a difficult, persistent invasive. This hardy weed will
grow quickly and easily in riparian areas, rapidly crowding out native species and
destroying wetland habitats. It has a high tolerance to harsh conditions, such as drought,
floods, high salinity, shade, and high temperatures and very few natural predators in the
Northeast. An extensive root system encroaching deep into the soil, coupled with a hardy,
fast-growing vegetative reproduction system makes eradication a frustrating affair.
Fortunately, at the Intervale the Japanese knotweed invasion is in its early stages so
overcoming the problem will require diligence, but hopefully not as much time and energy
as is usually needed for massive, 10-foot high shrubs.
IDENTIFICATION
Japanese knotweed is a dense perennial shrub that can grow up
to ten feet high.
Red woody stems resemble bamboo stalks (although not
related) and when young look like reddish tinged asparagus.
Hollow stems have raised nodes encircling the stem where
leaves shoot out.
Leaves are oval-shaped with a point and generally about six
inches long and three inches wide.
Lacy white or cream-colored flowers appear in late summer and
early fall (August-October), running down the stem.
METHODS OF REMOVAL
Mechanical removal of Japanese knotweed has proven to be a
long, multi-year process. In order to weaken the root system, it
is essential to cut back plants at the stem with a scythe, loppers,
or even a lawn mower at least once every 2-3 weeks during the
growing season (April through August) and should continue
thereafter with less frequency. Manual removal includes
pulling seedlings, rhizomes, and mature plants. Plants should
grow no more than six inches in height before removal.
DISPOSAL
Any portion of the Japanese knotweed plant, as small as ½ inch,
can re-sprout, starting new colonies. Bag any plant fragments; let
them rot for a year, and dispose of them in a landfill.
DO NOT COMPOST!
(Anderson, 2012; Invasives; Service, 2007; The Nature Conservancy)
Works Consulted
Anderson, H. (2012). Invasive Japanese Knotweed (Fallopia japonica). Best
Management Practices in Ontario Peterborough, ON: Ontario Invasive
Plant Council
Invasives, V. Japanese Knotweed (Polygonum cuspidatum). Retrieved April 5th
2015, from http://www.vtinvasives.org/invaders/japanese-knotweed
Service, N. R. C. (2007). Pest Management--Invasive Plant Control Japanese
Knotweed. Retrieved April 5th 2015, from
http://efotg.sc.egov.usda.gov/references/public/mn/797japaneseknotw
eed.pdf
The Nature Conservancy. Knotweed-invasive fact sheet. Retrieved April 5th
2015, from
http://www.nature.org/ourinitiatives/regions/northamerica/unitedstat
es/vermont/knotweed2010-1.pdf
Image Credits
Taken by Michael Gasperl on September 9th, 2005.
Distributed under a Creative Commons BY-SA 3.0 license.
Taken by MdE (Wikipedia user) on September 14, 2007.
Distributed under a Creative Commons BY-SA 3.0 license.
Taken by Annelis (Wikipedia user) on February 15, 2012.
Distributed under a Creative Commons BY-SA 3.0 license.
Taken by Liz West on August 25th, 2007. Distributed by a
Creative Commons BY 2.0 license.
Taken by Roger Kidd in 2007. Distributed by a Creative
Commons BY-SA 2.0 license.