 |
Japanese Knotweed - Polygonum cuspidatum
Sieb. & Zucc
Buckwheat
Family: Polygonaceae
Japanese knotweed is an extremely difficult plant to control due to its
ability to re-grow from vegetative pieces and from seeds. Mechanical and
chemical methods are most commonly used to eliminate it.
|
|
|
Common Names: Japanese knotweed,
Giant Knotweed, Mexican bamboo
Native Origin: Eastern Asia
Description: Japanese knotweed is an
upright, shrub like, 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 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
about 1/10 inch long. It reproduces primarily by seed
and by vegetative means with the help of long, stout
rhizomes. It can be transported to new sites by water,
wind, as a contaminant in fill-dirt, or on the soles of
shoes.
Habitat: It 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 home sites. It can quickly become an
invasive pest in natural areas after escaping from
cultivated gardens.
Photo: Jan Samanek, State Phytosanitary Administration,
Bugwood.org
|
|
|
Distribution: This species is
reported from states shaded on Plants Database map. It
is reported invasive in AK, CT, DC, DE, GA, IN, MA, MD,
ME, MI, MO, NC, NH, NJ, NY, OH, OR, PA, RI, TN, VA, VT,
WA, WI, and WV.
Ecological Impacts: It 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.
Control and Management: It is
difficult to control because of its ability to re-grow
from vegetative pieces and from seed.
• Manual-
Hand pull young plants; remove all roots and runners to
prevent re-sprouting
•
Chemical- It can be effectively controlled using any
of several readily available general use herbicides such
as glyphosate or triclopyr. Apply herbicides to freshly
cut stems or to foliage. Follow label and state
requirements.
Photo: David J. Moorhead,
University of Georgia, Bugwood.org
|
Description and
Biology
- Plant: a member of the
buckwheat family
(Polygonaceae), knotweed is
an upright, shrubby,
herbaceous perennial that
can grow to over 10 feet in
height. Stems of Japanese
knotweed are smooth, stout
and swollen where the leaf
meets the stem. Like all
members of the family, it
has a membranous sheath
surrounding the joints of
the stem.
- Leaves: although
variable, leaves are
normally about 6 inches long
by 3 to 4 inches wide,
broadly oval to somewhat
triangular and pointed at
the tip.
- Flowers, fruits and
seeds: 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.
- Spreads: primarily by
seed and by vegetative means
with the help of long, stout
rhizomes. It can be
transported to new sites by
water, wind, as a
contaminant in fill-dirt, or
on the soles of shoes. It
often escapes from neglected
gardens and discarded
cuttings.
- Look-alikes: Virginia
knotweed (Tovara
virginica), prince's
feather (Polygonum
orientale), and giant
knotweed (Polygonum
sachalinense,
non-native).
|
|
|
|
|
|
Prevention and Control
Japanese knotweed is an extremely difficult plant to
control due to its ability to re-grow from vegetative
pieces and from seeds. Mechanical and chemical methods
are most commonly used to eliminate it. Single young
plants can be pulled by hand depending on soil
conditions and root development. All roots and runners
must be removed to prevent re-sprouting. Glyphosate and
triclopyr herbicides have been used, applied either to
freshly cut stems or to foliage.
|
|
|
Beavers used Japanese knotweed to build this dam. Note
extensive infestation along the riverbank.
Photo: Mark Folsom, Bugwood.org
|
|
|