Vol. 51—1997 - NorthEastern Weed Science Society

124
EVA UATION OFGLYPHOSATEFOR DORMANf APPLICATIONS TO BRUSH
RESPROUTS
A.E. Gover, J.M. Johnson, C.W. Spackman, and L.J. Kuhns ll
ABSTRACf
The ob ective of this trial was to evaluate varying rates of a commercially available
isopropyl ine salt of glyphosate, and different carriers for their effect on brush control provided
by dorman season applications. Nine treatments were applied to a stand of second year resprouts
at the inter hange of SR 219 and SR 22, near Ebensburg, PA, on April 5, 1996. The treatments
were appli with a C02-powered, hand-held sprayer equipped with a Spraying Systems #55(X)
Adjustabl ConeJet, with a Y-2 tip. The herbicide solution was applied to provide complete
coverage the lower 24 to 36 in of each primary stem in a sprout cluster. Six treatments included
glyphosat alone, mixed at 10, 25, and 50 percent (v/v) of product"; which produced mixtures
containing 0.3, 0.75, and 1.5lb glyphosate ae/gal, respectively; or 0.4, 1.0, and 2.0 Ib of the
isopropyl ine salt/gal. These concentrations of g1yphosate were mixed with either water plus
QwikWet -399; or Thinvert R, a ready-to-use invert emulsion carrier. The butoxyethyl ester
formulatio of triclopyr-" was mixed at 5 percent (v/v) product, or 0.2 lb/gal, with 2 percent (v/v)
crop oil centrate in water, alone, or with 0.5 percent product (vIv) of the isopropylamine salt of
imazapyr4 , providing O.Ollb/gai. Additionally, g1yphosate plus imazapyr, at 10 plus 1 percent
product (v v), or 0.3 plus 0.02Ib/gal, respectively, were mixed with QwikWet M-399 and water.
The predo inant brush species were green ash (FraxinuspennsylvanicaMarsh.), black cherry
(PrunusS otina Ehrh.), red maple (AcerrubrumL.), sugar maple (AcersaccharumMarsh.), and
red oak ( uercusrubraL.). Plant heights ranged from 3 to 10 ft, with most plants falling in the 6
to 8 ft ran e. Each treated sprout cluster was rated September 14, 1996, using an injury scale of 1
to 10, in hich 'I' is no injury, and '10' indicates the treated plant is dead. Results are listed by
average i [ury, and by the most common individual species in Table 1.
When mixed with QwikWet M-399 and water, glyphosate alone produced average injury
ratings r ging from 8.9 to 9.6, while the average injury ratings ranged from 4.4 to 7.6 when
glyphosa was mixed with Thinvert R. Injury to red maple was somewhat less than on other
species at he two lowest glyphosate rates, and scattered stems of black birch (Betulalenta L.)
averaged injury rating of only 3.0 when treated with the 0.75Ib/gal rate of g1yphosate in
QwikWet M-399. The high rate glyphosate mixture did not spray as easily as the two lower rates
when mi d with QwikWet M-399. The glyphosate formulation did not mix well with the
Thinvert , as constant agitation during application was necessary to prevent separation,
particular yat the high g1yphosate rate. Triclopyr alone had an average injury rating of 5.2, and
triclopyr Ius imazapyr averaged 6.1, with most of the increased injury seen on ash. The
glyphosa plus imazapyr combination in QwikWet M-399 and water had a lower average injury
rating th the same rate of g1yphosate alone. Much of this difference was due to the presence of
red oak i the plot, which comprised about 20 percent of the stems, and had an injury rating of
only 5.7.
Furth r investigations need to be conducted to determine the range of species effectively
controlle by dormant applications of glyphosate, the effect of time of year on injury, as well as
whether ull circumference coverage of the treated stems is necessary on the smaller stems typical
of this tri .
11Project ssociate, Project Assistant, Research Technologist, and Professor of Ornamental Horticulture,
respe tively, The Pennsylvania State University, University Park, PA.
2/ Accord isopropylamine salt of glyphosate, 3lb ae/gallon, Monsanto Company, St. Louis, MO.
3/ Garlon , butoxyethyl ester of triclopyr, 4tb ae/gallon, DowElanco, Indianapolis, IN.
41 Stalker, isopropylamine salt of imazapyr, 2Ib ae/gallon, American Cyanamid, Princeton, NJ.