Vol. 51—1997 - NorthEastern Weed Science Society

101
EV
UATIONS OF GLVPHOSATE AND 2,4-0 FORMULATIONS
IN DORMANT CONIFERS
John F. Ahrens and Todd L. Mervosh'
ABSTRACT
In late 19 5, Monsanto Chemical Co. announced that gIyphosate no longer would be
available for 0 entals and turf as Roundup and would be replaced by Roundup PRO. Since
Roundup PRO h a higher concentration of surfactant and possibly a different surfactant,
selectivity ofgI hosate in dormant conifers might be altered. We also evaluated the selectivity in
dormant conifers of a non-surfactant form of glyphosate (Accord) with a commercial surfactant
(Induce) added. urther evaluations of2,4-0 amine andlor butoxy ethyl ester also were included
in our experimen s.
Field exp ents were conducted in 1996 at the Connecticut Agricultural Experiment
Station's Valley boratory and at commercial nurseries. In April, Roundup, Roundup PRO, and
Accord plus 0.5 0 v/v Induce were sprayed in 30 gallA over globe arborvitae (Thuja occidentalist
and upright yew Tams cuspidata var. capitata) [0.375 to 0.751b ailA] and over white spruce
(Picea g/auca) d Norway spruce (Picea abies) [0.5 to 1.5lb ai/A]. In addition, 2,4-0 at 0.5 to
2 lb aelA was ap lied over these dormant conifers. The spruces were selectively sheared one day
before treatment.
te experiment in spreading yew (Tams cuspidata), we compared butoxy ethyl
ester and amine rmulations of2,4-0. In this experiment the yews were heavily sheared 2 weeks
before treatment. In upright yew and the spruces, 2,4-0 caused no injury and controlled several
winter annual br eafweeds. In arborvitae, 2,4-0 at 0.51b aeiA caused only slight early injury.
Higher rates cau d early stunting and needle distortion which was barely evident in July. New
growth of sprea g yews was suppressed in June by all rates of 2,4-0. Growth suppression was
greater with the ster than the amine formulation. Plants recovered from the 0.5 and 1.0 lb aeIA
rates by July. W suggest that pruning dormant yews before treatment may increase early 2,4-0
injury.
Response of the conifers varied greatly to the gIyphosate formulations. Injury to the
spruces in the fo of dwarfed and chlorotic new growth was primarily associated with fresh
pruning wounds. Accord plus Induce and Roundup PRO injured more spruces than Roundup, but
injury was slight n average. Spruces are very tolerant of glyphosate and comparisons between
Roundup and Ro dup PRO are inconclusive at this time. In upright yew, no injury was observed
with any formula 'on at rates up to 0.751b ailA. In arborvitae, plant injury was greatest with
Accord plus Ind , intermediate with Roundup PRO, and least with Roundup. However, both in
yew and arborvit e, it appeared that rates of glyphosate could be reduced about 25% with
Roundup PRO a compared with Roundup to provide equivalent weed control with acceptable,
slight early plant ~ury.
I Emeritus Weed Scientist and Assistant Agricultural Scientist, The Connecticut Agricultural
Experiment Stati n, Valley Laboratory, Windsor, CT 06095.