Vol. 51—1997 - NorthEastern Weed Science Society

126
E ALUATION OF IMAZAMETH FOR WEED CONlROL IN WIlDFLOWER
ESTABLISHMENT
Chad W. Spackman, Jon M. Johnson, and Larry J. Kuhns 1J
ABSTRACT
As p of a cooperative project between the Pennsylvania State University and the
Pennsylv .a Department of Transportation, a study was initiated to evaluate imazamethv at 0.094
and 0.188 bs/ac for both pre and postemergent weed control in establishment of annual
wildflowe . All treatments contained a surfactantvand drift control agent41. The study area was
located at enn State's Landscape Management Research Center and was arranged in a randomized
complete lock design with three replications. The area was treated with 4lbs/ac glyphosate on
May 6, 19 6, to control all existing vegetation. On May 20 it was rototilled to a depth of 8 in, and
seededwi an annual wildflower mix containing cosmos (CosmosbipinnatusCav.), cornflower
(Centaure cyanus L.), corn poppy (Papaverrhoeas L.), rocket larkspur (Delphiniumajacis L.),
sweet aly sum (DianthusbarbatusL.), and tall plains coreopsis (CoreopsistinctoriaNutt.) at 14
lbs/ac, mergent treatments were applied May 31, as a few cosmos seedlings were emerging,
to 6 by 1 ft plots using a CO2-powered hand held sprayer equipped with Spraying Systems XR
8004 VS pray tips, delivering 40 GPA at 35 psi. Postemergent treatments were applied June 28
and all . dflower species, except rocket larkspur, were present within the treated plots.
Predomin t weeds included smooth pigweed (Amaranthuskybridus L.), common yellow
woodsorr I (OxalisstrictoL.), green foxtail (SetariaviridisL.), common lambsquarters
(Chenop ium albumL.) and common dandelion (TaraxacumofficinaleL.), and were uniformly
mixed ng the flowers. Ground cover ratings and average canopy heights of both wildflowers
and weed were taken June 28, July 25, and September 11. Results of the weed ratings are
reported i Table la and wildflower ratings in Table lb.
Ima eth provided excellent preemergence weed control through the September rating period.
Camp to the untreated check, the postemergence applications reduced weed height at the July
rating, bu not weed cover. By September, there were no differences in weed cover or height
between e postemergence treated areas and the untreated check. Ground cover by wildflowers
was not s gnificantly different for treatments at either the June or September rating periods,
however e 0.188 lb/ac post treatment had less cover in July than the pre and untreated plots. Pre
treatmen provided the lowest wildflower canopy heights in June but were not different from the
check in eptember, while the post treated plots stunted the wildflowers and provided the lowest
canopy h ights in both July and September. Overall, there was little difference between application
rate for ether the pre or postemergent treated plots for all ratings of weeds and wildflowers. It was
observed that treated plots did affect the growth of the wildflowers compared to the untreated
check; e .ally cosmos, which had a noticeable increase in stem diameter and axillarybranching
near the ase of the stem. A germination test was conducted indoors and all wildflower species
germina ; however, rocket larkspur did not germinate in any field plots, including the check. All
other s .es were present within the untreated and postemergent treated plots and these same
species, xcept sweet alyssum, were present within the preemergent treated plots. Weed species
present a the end of the study were identical to the initial species.
A mergent treatment at either application rate provided a significant decrease in the amount
of weeds and provided comparable amounts of wildflowers to the untreated check. Sweet alyssum
does not ppear to be tolerant to a preemergent treatment so species must be carefully selected
when se .ng, Postemergent applied treatments showed no improvement of weed control
comp to the check and temporarily thinned the wildflowers.
11Re Technologist, Project Assistant, and Professor of Ornamental Horticulture, respectively, The
Pen lvania State University, University Park, PA.
21Plateau American Cyanamid Co., Wayne, NJ.
31Qwik et 357 (Exacto Inc.) @ 0.125% (v/v).
41Poly AlOOI (Exacto Inc.) @ 0.25% (v/v).