1. City of Bridgeport
Veterans Memorial Park
Control Methods and Maintenance of
Japanese Knotweed, Polygonum cuspidatum
It is with recommendation as a supplement to the Invasive Species Control Plan
provided to the City prepared by GZA GeoEnvironmental, by certified soil
scientist Stanley Dynia, additional control methods and maintenance is
considered to eliminate and potentially eradicate delineated patches of
Japanese Knotweed, Polygonum cuspidatum found on Site.
PHASE I point no. 8 of the Invasive Plant Management Plan calls for excavation
of the noxious and invasive plant species, segregate excavated soil with residual
plant parts removed to a non sensitive location offsite. The specified contractor,
Giordano Construction, is and was required to remove all plant material and soil
underlying the plants to a minimum depth of 36 inches. All contaminated fill
material from the specified area is not to be reused at the site.
Should contaminated fill material be reused on site it is recommended to
consider the material ‘actively invasive’ given that stem or root fragments can
also be spread in contaminated fill material. Japanese Knotweed has an
extensive rhizome system potentially spreading between 23’ - 65’ away from the
parent plant and potentially penetrating at least 7’ into the soil. Knotweed can
rapidly reproduce vegetatively from root and stem fragments as small as ½”
forming new plant colonies. Broken and/or cut stems and roots will sprout if left
in moist soil or directly placed in water.
Given that Knotweed is a creeping perennial it has a specified growing season,
April – August, and dies back to the ground with the first hard frost. It is
recommended that a Noxious Weed Management Control Plan be established
by the City for all invasive plant species delineated on the Site.
REMEDIATION TECHNIQUES AND APPLICATIONS
Reuse of actively invasive fill material should be buried a minimum depth
of 10’ and at least 20’ feet away from the original patch center. To
prevent new growth it is recommended the contaminated fill material be
covered with a filter fabric extended at least 6’ beyond the perimeter of
the fill material. Frequent cutting and/or mowing is required to control
resprouting.
2. Between the specified growing seasons, April – August, cutting and
maintenance should occur at least twice a month to control resprouting.
It is recommended that hand cutting should be done at least every 2-3
during the growing season. Sprouting slows after August and
maintenance can be scaled back at that time.
Remove, rake and dry all Knotweed that is cut or mowed to prevent
reestablishment.
When cutting and mowing, cut as low as possible and specified as
above.
Digging and pulling major rhizomes systems by the root crown will reduce
the root mass.
Herbicide application methods include spraying, wicking, injecting,
pouring or combinations of.
Herbicides must be applied by a licensed applicator; consultation of
product use can be located at the Department of Agriculture, local
extension agent, pesticide dealer, or herbicide manufacturer.
Consult the label on herbicides for application methods including:
o Correct concentration rates
o The right application method
o The correct timing to coincide with plant susceptibilbity
o An adjuvant if recommended
Adjuvants are spray solution additives that may make herbicides more
effective they move the chemical from the leaves into the root systems
(i.e. being translocated).
SOURCES
Soll, Jonathan. 01.16.04 Controlling Knotweed in the Pacific
Northwest. The Nature Conservancy of Oregon.
ADDITIONAL RESOURCES
Child, Lois and Max Wade. 2000 The Japanese knotweed manual –
the management and control of an invasive alien weed. Packard
Publishing Limited
