Background
Polygonum cuspidatum, or Fallopia japonica
tall-growing, hollow-stemmed, perennial herbaceous plant
native to East Asia,
introduced to the U.S. for use as ornamentals during the late 1800’s
A rhizome is an underground stem that gives rise to roots, aerial stems, and more rhizomes.
tall-growing, hollow-stemmed, perennial herbaceous plant
native to East Asia,
introduced to the U.S. for use as ornamentals during the late 1800’s
A rhizome is an underground stem that gives rise to roots, aerial stems, and more rhizomes.
Problems
It is listed by the World Conservation Union as one of the world's worst invasive species.
The invasive root system and strong growth can damage concrete foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites
In the UK Several banks have refused mortgage applications on the basis of the plant being discovered in the garden or neighbouring garden.[31]
Knotweed reduces sight distance and damages pavement along roads
overruns lowto-no maintenance areas,
crowds out existing plant communities.
A very small piece of rhizome that is moved to another site will give rise to a new plant.
Roadside maintenance such as ditch cleaning is one the primary ways that knotweed is spread.
Established knotweed stands are extremely tenacious.
While the towering stems of the plant look menacing, the real issue is the underground rhizome that can grow lightning fast and invade new areas.
The invasive root system and strong growth can damage concrete foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites
In the UK Several banks have refused mortgage applications on the basis of the plant being discovered in the garden or neighbouring garden.[31]
Knotweed reduces sight distance and damages pavement along roads
overruns lowto-no maintenance areas,
crowds out existing plant communities.
A very small piece of rhizome that is moved to another site will give rise to a new plant.
Roadside maintenance such as ditch cleaning is one the primary ways that knotweed is spread.
Established knotweed stands are extremely tenacious.
While the towering stems of the plant look menacing, the real issue is the underground rhizome that can grow lightning fast and invade new areas.
Control Methods
The key to controlling knotweed is controlling the rhizome system of the plant.
Knotweed is best thought of as being like an iceberg - what you can see is only the tip of the problem
use as many methods as possible
Cutting alone is not an effective tool for managing knotweed. However, cutting can be an integral part of managing this plant,
knotweed can be mowed.
A June 1 cutting of 6 to 10 ft tall knotweed results in regrowth that is only 2 to 4 ft tall.
lateAugust mowings and had almost no regrowth to treat.
Herbicides can be applied to the plant foliage or to the surrounding soil.
The most common herbicide application is to spray the foliage.
When knotweed has been cut and the shorter regrowth is being treated, a backpack sprayer may be the tool of choice. The shorter canopy can be effectively treated with a low-volume spray (5 to 40 gallons per acre),
Glyphosate is the herbicide of choice for controlling knotweed. It is effective, has no soil activity, can be used near water, it is readily available, and inexpensive (Table 1). The herbicide is considered non-toxic to pets and humans, but as a precaution please keep them out of the area until the herbicide has soaked in.
- Cornerstone (EPA 42750-60-1381) active ingredient glyphosate 41% (2.5 gallons, $45- Ashland Ag Center on Sanborn Ave) Round up Concentrate Plus (EPA 71995-29) active ingredient glyphosate 18% (16 oz, $20- hardware stores)
A follow-up application the first season after the control treatments is critical. The timing of maintenance herbicide applications follows the same calendar as the control applications - after July 1.
In some cases weekly mowing can eventually draw down enough of the plant’s reserves to kill it.
Stem and root fragments as small as ½ inch can sprout so special care must be taken to contain the plant parts when using manual control. Do not allow plant parts to enter waterways during control. Limit soil contact when drying the plant parts. Small plants may be hung in trees to prevent re-rooting. Cut stems may be piled on a raised platform, brush pile or tarp for drying. Do not compost plant materials as they may sprout and then spread. Piles may be burned. Do not remove soil or plant material from the site unless being disposed of in a landfill.
Sources:
http://plantscience.psu.edu/research/projects/vegetative-management/publications/roadside-vegetative-mangement-factsheets/5managing-knotweed-on-roadsides