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

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COMPARISON OF INTEGRATED WEED MANAGEMENT STRATEGIES IN
CHRISTMAS TREE PLANTATIONS. M.W. Marshall, B.H. Zandstra, Michigan State
Univ., East Lansing, and R.J. Richardson, North Carolina State Univ., Raleigh.
ABSTRACT
Since Christmas tree value is based mainly on their appearance, pests that reduce
the visual quality of trees are intensively managed. Michigan Christmas tree growers rely
heavily upon pesticides, including atrazine and simazine, to control these pests. However,
atrazine and simazine have ground and surface water concerns. Field studies were
conducted in 2005 and 2006 to determine integrated weed management programs
utilizing alternatives to replace and/or reduce triazine use. The treatments were
flumioxazin+glyphosate at 0.28 and 1.12 kg/ha broadcast or within the row, organic
mulch, organic mulch+glyphosate at 0.84 kg/ha, hard fescue (Festuca brevipila 'Aurora
Gold') groundcover, white clover (Trifolium repens L.) groundcover, mechanical control
system, mechanical control+glyphosate at 0.84 kg/ha, and an untreated control. Organic
mulch consisted of a coarsely ground pine bark and was applied as a 91 cm wide band in
the tree rows. Hard fescue and white clover were broadcast seeded into plots in the fall of
each year at rates of 250 and 7 lb/A, respectively. Mechanical control treatments were
imposed using a hand-operated mower between and within the tree rows. Flumioxazin
and glyphosate treatments were applied on April 19, 2005 and April 11, 2006.
Glyphosate+mechanical treatments were imposed in June, July, and August of each year.
Experimental design was a randomized complete block design with 4 replications. Conifer
injury was evaluated 8, 12, and 16 wk after treatment (WAT) on a 0-100% scale (0 = no
injury and 100 = crop death). In addition, plots were visually evaluated for % cover of
each weed. Overall ground cover in the 2005 site was denser than in the 2006 site. In
general, hard fescue established and provided a denser groundcover than white clover. In
the hard rescue plots, other weed species did not thrive in the plots; however, quackgrass
(Elytrigia repens (L.) Nevski.) was observed at a low percentage of the total groundcover
(8%). This indicates that a living mulch, such as hard fescue inhibited light-dependent
weed seed germination. The organic mulch provided excellent groundcover until weed
seeds started germinating within the mulch layer. In the mulch+glyphosate treatment,
glyphosate eliminated most of the weeds emerging between the rows and within the
mulch layer. Plots receiving flumioxazin + glyphosate treatments, regardless of the
broadcast or strip application, remained bare with the exception of a few weeds
throughout the growing season. Conifer injury was virtually non-existent in all treatments.
Similar to 2005, hard fescue provided greater than 65% groundcover throughout the
growing season. Common milkweed (Asclepias syriaca L.) was observed in some of the
hard fescue plots (less than 10%). The use of a living groundcover, such as hard fescue,
is a beneficial cultural control because it minimizes herbicide use while providing
suppression of light germinating weed species. For suppression of perennials, such as
quackgrass and common milkweed, hard fescue is also tolerant to over-the-top
applications of glyphosate.
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