Vol. 54—2000 - NorthEastern Weed Science Society

present at the initiation of the study, these plots had the residue from an another season of
growth, compared to the sequences initially sprayed in the spring. This residue was abundant
enough to appear to inhibit establishment of the seed mix, rather than serving as a protective
mulch.
The Japanese knotweed at the Etna site was not satisfactorily controlled, particularly in the
undisturbed areas, and the grass mixture never hadan opportunity to establish. Knotweed in the
undisturbed stands was reduced in height by about 20 percent compared to the height at
treatment on 5/14/98, but had greater than 90 percent cover. In the on-ramp area, which was
somewhat open to begin with, cover from the grass mixture was 90 to 95 percent for the SIP/F,
P=SIF, and PIFISsequences on June 24, 1999, 14 months after study initiation. Knotweed cover
averaged 25 percent for these three sequences, and retreatment was definitely needed.
A contributing factor to the reduced success at the Etna site may be that the knotweed was
much larger thanthe knotweed at the Doylestown site when the spring herbicide treatments were
applied. making uniform coverage with a low volume application difficult. Another factor may
be that Japanese knotweed is more tolerant to dicamba and clopyralid than Sakhalin knotweed.
When the results of this study are considered collectively with previous disappointing results
with dicamba plus clopyralid on Japanese knotweed in field day-type demonstrations in
northeastern and southeastern PAt it becomes apparent that the approach of regarding the two
knotweed species as basically identical in terms of management may be seriously flawed.
SUMMARY
When evaluated in August. 1999. rehabilitation sequences initiated in April. 1998 in a stand
of Sakhalin knotweed had resulted in better establishment of the seeded fine fescue mixture than
the sequence initiated at the end of August, 1998. TIIis difference is probably temporary, as
knotweed reduction was excellent in all four sequences, and the grassin the later-initiated
sequence should come to be as well established as the spring-initiated sequences during the 2000
growing season. When an effective herbicide combination is utilized, vegetation managers have
considerable flexibility in their approach to rehabilitating knotweed infested sites. As long as
managers acknowledge the tenacity and persistence of invasive species such as knotweed, use an
adapted seed mix, and seed at the right time, they can successfully rehabilitate sites using a
variety of sequences.
ACKNOWLEDGMENTS
This research was funded hy the Pennsylvania Department of Transportation,
Maintenance and Operations.
Bureau of
LITERATURE CITED
McKee,G.W., J.V. Raelson, W.R. Berti, and R.A. Peiffer. 1982. Tolerance of Eighty Plant
Species to Low pH, Aluminum, and Low Fertility. Agronomy Series No. 69, The
Pennsylvania State University.
80