Vol. 54—2000 - NorthEastern Weed Science Society

COMPARISON OF REHABILITATION SEQUENCES FOR JAPANESE AND SAKHALIN
KNOTWEED INFEST ATIONS
A.E. Gover, J.M. Johnson, and LJ. Kuhns'
ABSTRACT
Fouroperationsequences to convertroadsidesites infestedwithJapaneseknotweed
(Polygonum cuspidatum Sieb. & Zucc.) and Sakhalin knotweed (Polygonum sachalinense
F.Schmidtex Maxim.)to a grassmixturewerecompared.Thefoursequenceswere developed
by varyingtheorderof a primaryherbicidetreatment,grassseeding,anda follow-upherbicide
treatment. Sixteen monthsafterinitiationof the trial,threesequences featuringprimary
treatment in the spring of the first year provided at least 60 percent grass cover, and less than 10
percentSakhalinknotweedcover at a southeasternPA site. The fourthsequence, featuringa late
summerprimarytreatment,providedequalknotweedsuppression,butonly 18 percent grass
cover. A second trialon Japaneseknotweedin a highway interchangecomplex in southwestern
PA was largely unsuccessfulto poorknotweedcontrol.
INTRODUCTION
Japanese and Sakhalin knotweeds are stout, erect, herbaceous perennials that commonly grow
to beights of2 to 3 m. They spread vigorously by vegetative means, and are capable of
producingdense monoculturescoveringseveralhectares. Both species occur on desolate,
disturbed sites, and Japanese knotweed has been documented to tolerate extremes in low pH and
iniertility (McKee, et. al, 1982). In a roadside setting, particular%.~ narrow right-of-ways, both
species can pose a seriousproblemdue to loss of sight distance, age to asphaltpavements
fromemerging shoots. andenvironmentaldegradationdue to reductionin biodiversity. As part
of an ongoing project fundedby the Pennsylvania Department of Transportation, four
rehabilitationsequencesto convertknotweed-infestedroadsidesto a grassmixturewere
compared at two sites, one in Doylestown, PA (near Philadelphia), and one in Etna, PA (near
Pittsburgh).
MATERJALS AND METHODS
Each of the fourrehabilitationsequencesconsisted of threeoperations;1) a primaryherbicide
treatment to kill the above-ground growth ofknotweed and provide an opportunity for a seeding
to beestablished, 2) the seeding ofa 55/35/10 mixture of hardfescue (Festuca brevipila Tracey),
red fescue (Festuca rubra sap.rubra L.), and annual ryegrass (Lo/ium multiflorum L.), seededat
112 kglha, and 3) a follow-up herbicide application to provide control of the inevitable knotweed
resproutsandfurtherreducethevigorof theundergroundorgans. An integralelementof any
invasive species rehabilitationprojectis continued(perpetual)maintenanceafterthe desired
replacement species has been established.
Table1 lists thecode namesandgeneralizedtimetableof the sequences,as well as the
treatment dates for both sites. The Doylestown site was located in a stand of Sakhalin knotweed
on a fill slope originally seeded to crownvetch along SR 611. Individual experimental plot were
6 by 9 m, and were arranged in a randomized complete block with four replications. At study
initiationon April 6, 1998, knotweedemergencewasjust beginning,withshoots extending up to
0.2 m. Knotweed residuefrompreviousseasons providednearlycomplete cover. On April 30.
when the first herbicide treatments were made, the knotweed sboots ranged in height from 0.2 to
1.0 m. On August 31, previously untreated knotweed averaged 2.5 m in height.
1ProjectAssociates andProfessorof Horticulture, respectively,ThePennsylvaniaStateUniversity,UniversityPark,
PA.
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