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.

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