Vol. 54—2000 - NorthEastern Weed Science Society

Table I: Sequence codes and generalized timing for the primary treatment, follow-up treatment,
and grass mixture seeding for the four rehabilitation sequences compared. Listed below the
generalized times are the actual operation dates for the Doylestown and Etna sites. In the
sequence codes, 'P' indicates primary herbicide treatment, 'F' follow-up herbicide treatment, and
'S' seeding, and '=' indicates the two operations can occur during the same site visit.
Pnmary Follow-up GraSs
Sequence Treatment Treatment Seeding
SIPIF knotweed leaf-out late summer early spring
Doylestown 4/30/98 8/31/98 4/6/98
ElM 5/14/98 9/1/98 4/15/98
P~SIF knotweed leaf-out late summer knotweed leaf-out
Doylestown 4/30/98 8/31/98 4/30/98
ElM 5/14/98 9/1/98 5/14/98
PIFIS knotweed leaf-out late summer late swnmer
Doylestown 4/30/98 8/31/98 9/14/98
ElM 5/14/98 9/1/98 9/1/598
P/SIF2 late summer late summer/fall spring year 2
Doylestown 8/31/98 6/10/99 9/14/98
ElM 911/98 6/24/99 9/15/98
The Etna site was located in the interchange complex of SR 8 and SR 28, on the north bank
of the Allegheny River. Each of the three replications were located in a separate stands of
Japanese knotweed. Average plot size was 95 m 2. Two of the knotweed patches were
undisturbed, while the third was located at the convergence of two on-ramps and was routinely
mowed two to three times per year. The P/SIF2 sequence plots were cut to a height of about 0.3
m on May 14 in all three replications, to simulate the mowing that untreated knotweed would
otherwise receive where sight distance would be compromised. At study initiation on April IS,
1998, knotweed was already 1 to 1.3 m in height in the undisturbed areas. The canopy was still
somewhat open as Japanese knotweed shoots appear to elongate more before leaf expansion,
compared to Sakhalin knotweed. When the primary herbicide treatments were made to the
SIPIF, P~SIF, and PIFISsequences on May 14, 1998, the knotweed ranged from 2.0 to 2.5 m in
the undisturbed areas, and 0.8 to 2.0 m in the on-ramp area. Previously untreated knotweed was
1.510 2.0 mon September 1, 1998.
Herbicide treatments were applied with lever-actuated backpack sprayers, equipped with a
single Spraying Systems #5500 Adjustable ConeJet with an X-6 tip, with a targeted carrier
volume of 187 Llha. Both primary and follow-up treatments were a mixture of dicamba (3,6­
dichloro-2-methoxybenzoic acid) plus clopyralid (3,6-dicWoro-2-pyridinecarboxylic acid) at 2.2
plus 0.21 kg/ha, respectively. All applications included an organosilicone-based surfactant at 0.1
percent vivo Seed was pre-weighed for each plot, and distributed by hand.
RESULTS AND DISCUSSION
There was considerable contrast in the outcome between the two sites. At Doylestown, all
four sequences provided 93 to 97 percent reduction of Sakhalin knotweed by August 5, 1999, 16
months after initiation of the trial. The SIPIF, P=SIF, and PIF/S sequences were rated between
60 and 70 cover by the seeded grasses, while the P/SIF2 sequence was rated at only 18 percent
cover. This was due in part to the later establishment date and the dry fall of 1998, and also
because there was more knotweed residue in the P/SIF2 plots. In addition to residue already
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