City of Bridgeport Veterans Memorial Park Control Methods and Maintenance of Japanese Knotweed, Polygonum cuspidatumIt is with recommendation as a supplement to the Invasive Species Control Planprovided to the City prepared by GZA GeoEnvironmental, by certified soilscientist Stanley Dynia, additional control methods and maintenance isconsidered to eliminate and potentially eradicate delineated patches ofJapanese Knotweed, Polygonum cuspidatum found on Site.PHASE I point no. 8 of the Invasive Plant Management Plan calls for excavationof the noxious and invasive plant species, segregate excavated soil with residualplant parts removed to a non sensitive location offsite. The specified contractor,Giordano Construction, is and was required to remove all plant material and soilunderlying the plants to a minimum depth of 36 inches. All contaminated fillmaterial from the specified area is not to be reused at the site.Should contaminated fill material be reused on site it is recommended toconsider the material ‘actively invasive’ given that stem or root fragments canalso be spread in contaminated fill material. Japanese Knotweed has anextensive rhizome system potentially spreading between 23’ - 65’ away from theparent plant and potentially penetrating at least 7’ into the soil. Knotweed canrapidly 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 leftin 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 isrecommended that a Noxious Weed Management Control Plan be establishedby 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