Vol. 51—1997 - NorthEastern Weed Science Society

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118
EVALUA
ON OF HERBICIDES FOR CONTROL OF CANADA THISTLE IN FINE FESCUE
Chad W. Spackman, Jon M. Johnson, and Larry J. Kuhnsl/
ABSTRACf
As part of a cooperative project between the Pennsylvania State University and the
Pennsylv .a Department of Transportation, a trial was established to evaluate several herbicides
for selectiv control of Canada thistle (CirsiumarvenseL.) within a stand of fine fescue. The
study area as located within an established stand of fine fescue, comprised predominantly of hard
fescue (Fe tucalongifoliaThuill.), at Penn State's Landscape Management Research Center and
arranged' a randomized complete block design with three replications. Treatments included an
untreated c eck, 0.75 lbs/ac diglycolamine salt of dicamba (dicamba), 0.35 lbs/ac SAN 1269H
alone and' combination with O.5lbs/ac dicamba, 0.23lbslac clopyralid, 0.75lbs/ac dicamba in
combinati n with 0.12Ibs/ac clopyralid or 0.0121bs/ac metsulfuron methyl, 2lbs/ac glyphosate, 1
lb/ac tricl yr, and 0.1881bs/ac imazameth. All treatments, except glyphosate, contained 0.125%
(v/v) surf tant21and all contained 0.25% (v/v) drift control agent 3 /. Application was made to 6 by
10 ft plots n June 12, 1996, using a C02-powered hand held sprayer equipped with Spraying
Systems 8004 VS spray tips, delivering 40 GPA at 35 psi. Ground cover ratings of the fine
fescue we taken June 12; July 24, 43 days after treatment (DAT); and August 30, 79 DAT. An
initial cou t of thistle stems within the plots was taken June 12. A count of uncontrolled thistle
stems and istle resprouts was taken July 24 and August 30. These values were utilized for
determinin percent thistle resprouts and percent thistle decline, which evaluates the extent of
decline of e originally treated stems and was affected by either treatment or natural senescence.
Percent de line and resprouting results are reported in Table 1.
All tre tments, except triclopyr or imazameth, provided similar levels of thistle decline at the
July 24 ra ng. Triclopyr was slightly lower, while imazameth was not different from theuntreated
check. D to natural senescence of the thistle plants, an increase in thistle decline was evident at
the Augus rating, as the untreated check escalated from 15 percent decline in July to 64 percent in
August. I other treatments, excluding the check and imazameth, provided similar levels of
decline at e August rating. Percent thistle resprouting values at the July rating were similar for all
treatments except triclopyr with the highest level at 37 percent. There was no significant
difference among treatments at the August rating except for imazameth, which actually resprouted
by 151 pe nt. None of the treatments thinned the fine fescue stand but imazameth provided
slight n sis to the leaf tips.
All tre tments, except imazameth, provided selective control of treated thistles; but all still had
significan resprouting occur. No treatment provided an overall acceptable level of control,
therefore peat applications would benecessary to eliminate the thistle.
1/ Researc Technologist, Project Assistant, and Professor of Ornamental Horticulture, respectively, The
Penns lvania State University, University Park, PA.
21Qwik:W 357 (Exacto Inc.)
3/ Polytex 1001 (Exacto Inc.)