Vol. 51—1997 - NorthEastern Weed Science Society

115
CONTROLL NO ROADSIDE VEOEf ATION WITH THIAZOPYR, OXYFLUORFEN,
OLUFOSINA TE, AND OLYPHOSA TE
Larry J. Kuhns and Tracey L. Harpster!
INTRODUCTION
must be controlled under guiderails to allow water to flow uniformly away from
the road surface d to allow their clear visibility to drivers. The objective of this study was to
evaluate the resid al activity of two preemergence herbicides, oxyfluorfen and thiazopyr, in the
roadside enviro ent. They were used in combination with one of two postemergence herbicides,
glufosinate or gly hosate 2 , to eliminate existing weeds in the treated areas.
MEfHODS
The pree ergence treatments evaluated were thiazopyr alone at 0.5, 1.0 and 2.0 lb/a; the
same treatments p us oxyfluorfen at 1.61b/a; oxyfluorfen alone at 1.6Ib/a; and oryzalin plus
oxyfluorfen at 4 d 1.61b/a, respectively. The postemergence treatments included the addition of
glyphosate at 2 lb to a set of the preemergence treatments, or applications of either glyphosate at 2
lb/a or glufosinat at 2 lb/a 11 days prior to the application of the preemergence treatments. Table 1
includes a summ of the treatments.
Treatmen were applied to 75 ft2 plots with a C02 pressurized test plot sprayer at 30 psi
through two 8004 nozzles mounted in a double swivel nozzle body to eliminate the shadow effect I
around support ts; in 38 OPA. The combination of preemergence herbicides and glyphosate
was applied on Ju e 27,1996. At the same time, the applications of glyphosate or glufosinate
alone were made. On July 8, the preemergence treatments were applied over the areas previously
treated with glyp sate or glufosinate. Treatments were applied in a randomized complete block
design, with thr replications.
The study was conducted along a roadside under guiderails in two areas about 400 yards
apart. Two replic tions of the treatments including glyphosate were in one area, and the other
replication plus al three replications with glufosinate were in the other. The predominant weeds in
the glyphosate ar at the time of application were common ragweed (AmbrosiaartemisiifoliaL.),
birdsfoot trefoil ( tus comiculatusL.), wild carrot (DaucuscarotaL.), and crownvetch (Coronilla
varia L.). Other eeds distributed throughout were wild buckwheat (Polygonumconvolvulus
L.), common spe well (VeronicaofficinalisL.), bull thistle (Cirsiumvulgare(Savi) Tenore.),
common burdock (Arctiumminus (Hill) Bemh.), goldenrod (Solidagospp), green foxtail (Setaria
viridis (L.) Beau .), red fescue (FestucarubraL.), and garlic mustard (Alliariapetiolata (Bieb.)
Cavara & Grand . Ragweed was 6 to 12 inches tall, all others were 3 to 6 inches tall. The
predominant w s in the glufosinate treated area were wild carrot, common ragweed, spotted
knapweed (Centa reamaculosaLam.), birdsfoot trefoil, and yellow foxtail (Setarialutescens
(Weigel) Hubb.). The weed density and size in this area was lower than in the area treated with
glyphosate.
1996.
The perce t green cover in each plot was rated on July 22, August 22, and October 24,
1 Prof. of Ornamen Horticulture and Research Associate, Dept. of Horticulture, The Pennsylvania State
University, Universi y Park, PA 16802"
2 Roundup Pro, M nsanto Co., 800 No. lindbergh Boulevard, scLouis, MO 63167.