Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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2006 WEED MANAGEMENT TRIALS IN CHRISTMAS TREES. J.F. Ahrens,
Connecticut Agric. Experiment Sta., Windsor.
ABSTRACT
Several field experiments were conducted with older and new herbicides in
attempts to improve our knowledge of weed management options in Christmas tree
plantings. Trees were sprayed over the top at 30 gal/A. Randomized complete block
designs with four replications and three to six plants per plot were standard.
The 2006 season in CT was characterized by an extremely wet May and June
and a dry July which resulted in a major summer outbreak of annual weeds regardless
of early spring preemergence treatments. For the fourth season, we evaluated Westar,
a 1:10 ratio of sulfometuron methyl and hexazinone, as well as a 1:20 ratio. Westar at 8
oz/A (sulfometuron 0.5 oz ai/A and hexazinone 5.4 oz ai/A) gave excellent control of
quackgrass (Elytrigia repens L.) and at 12 oz/A caused no injury to established Douglas
fir (Pseudotsuga menziesii). Comparisons of fall versus April applications of
sulfometuron plus hexazinone confirmed that fall applications give poor control of
summer annual weeds. Adding non-ionic surfactant or glyphosate (Roundup Original)
at 1 pt/A to dormant applications did not affect injury to Fraser fir (Abies fraseri). Control
of large crabgrass (Digitaria sanguinalis (L.) Scop) was improved by increasing the rate
of hexazinone in the mix to 7.5 oz ai/A, but, in 2006, crabgrass control in late season
was poor at all rates. Westar alone or plus added hexazinone is a good option for
Christmas tree plantations but we will suggest it primarily for conifers established one or
more seasons in the field.
In another experiment, asulam at 4, 6, or 8 lb ai/A, on June 30, controlled
emerged large crabgrass with no injury to actively growing Fraser fir. Asulam could be
useful for postemergence control in transplant beds or in the field.
V-10142 75 WG (Valent U.S.A. Corp.) at 0.5 to 2.0 lb ai/A, halosulfuron 75 WG at
0.75 to 3.0 oz ai/A and sulfentrazone 4F at 0.125 to 0.5 lb ai/A were evaluated for
phytotoxicity in Douglas fir and Fraser fir plantations in IR-4 trials. None injured the
dormant conifers in April, but when reapplied over actively growing trees in June, 8
weeks later, halosulfuron injured Douglas fir, and V-10142 and halosulfuron injured
Fraser fir. Sulfentrazone, in June, caused little injury at 0.125 lb ai/A but did not control
crabgrass or common ragweed (Artemisia artemisifolia L.).
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