Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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EVALUATION OF HERBICIDES FOR CONTROL OF JAPANESE KNOTWEED. J.M.
Johnson, A.E. Gover, and L.J. Kuhns, The Pennsylvania State Univ., University Park.
ABSTRACT
As part of an ongoing research project funded by the Pennsylvania Department
of Transportation, a study was established to investigate the effectiveness of several
herbicides and tank mixes for controlling Japanese knotweed (Polygonum cuspidatum
Sieb & Zucc., POLCU).
This trial was established on a well-established stand of Japanese knotweed
located on an island of the Susquehanna River within Milton State Park, Milton, PA.
POLCU ranging from 2.4 to 3.7 m was mowed to the ground on June 8, 2005, and 2.7
by 7.6 m. plots were laid out in a randomized complete block design with three
replications. POLCU regrowth height averaged 0.8 m, and average cover ranged from
37 to 89 percent when sprayed on August 17, 2005. Treatments were applied as a
foliar spray using a CO 2 -powered, hand-held, fixed-width boom equipped with TeeJet
XR8004 VS tips delivering 281 l/ha at 172 Kpa. Herbicide treatments (kg ae/ha)
included fluroxypyr at 0.31; a premix of dicamba plus diflufenzopyr at 0.14 plus 0.056,
0.21 plus 0.084, or 0.28 plus 0.11; fluroxypyr at 0.31 plus the premix of dicamba plus
diflufenzopyr at 0.21 plus 0.084; dicamba (diglycolamine) at 2.2; dicamba at 1.1 and the
premix of dicamba plus diflufenzopyr at 0.28 plus 0.11; glyphosate at 3.4; and fosamine
at 6.0 alone or with imazapyr at 0.070. A methylated seed oil 1/ was added to all
treatments at 2.3 l/ha, except those containing fosamine, which included a non-ionic
surfactant 2/ at 0.25 percent, v/v.
Visual ratings of percent initial cover by POLCU and percent POLCU injury were
taken August 17 and September 23, 2005, 0 and 5 weeks after treatment (WAT),
respectively. Percent POLCU cover and biomass reduction were evaluated July 24,
2006, 49 WAT. These data were subjected to analysis of variance, and means were
compared using Fisher’s Protected LSD (p=0.05) (Table 1).
At 5 WAT, percent injury ranged from 33 to 99 percent. Dicamba alone at 2.2 (kg
ae/ha), or at 1.1 with the premix of dicamba plus diflufenzopyr at 0.28 plus 0.11; and
glyphosate at 3.4 provided the greatest initial injury with values from 93 to 99 percent.
At 49 WAT, the best-rated treatment was glyphosate at 3.4 (kg ae/ha), with
percent POLCU cover and reduction ratings of 1 and 99 percent. Dicamba plus
diflufenzopyr at 0.14 plus 0.056, or 0.21 plus 0.084 alone or in combination with
fluroxypyr at 0.31 were the only treatments rated significantly different, with average
POLCU cover values ranging from 44 to 70 percent, and percent POLCU reduction
ranging from 57 to 67 percent. All other treatments averaged 4 to 38 percent POLCU
cover and 80 to 96 percent POLCU reduction.
1/ Meth Oil, BASF, Research Triangle Park, NC
2/ Activator 90, Loveland Industries Inc., Greeley, CO.
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