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

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HERBICIDES AS ALTERNATIVES TO METHYL BROMIDE FOR WEED CONTROL IN
CONIFER SEEDLING BEDS. D.A. Little, M.W. Marshall, Michigan State Univ., East
Lansing, R.J. Richardson, North Carolina State Univ., Raleigh, and B.H. Zandstra,
Michigan State Univ., East Lansing.
ABSTRACT
The removal of methyl-bromide (MeBr) from the market has left some Christmas
tree growers looking for alternatives for weed control. In 2004 and 2005, a field study
was conducted at the Michigan State University Southwest Research and Extension
Center located near Benton Harbor to evaluate herbicides as alternatives to MeBr for
weed control in conifer seedling production. In early June 2004, a standard treatment of
MeBr:chloropicrin (98:2) was applied at a rate of 392 kg/ha. Treatments tested were
flumioxazin (0.28 kg/ha), granular oxadiazon (2.24 kg/ha), oxyfluorfen (1.12 kg/ha),
oxyfluorfen plus dithiopyr (0.28 kg/ha), oxyfluorfen plus metolachlor (1.68 kg/ha),
mesotrione (0.28 kg/ha), metolachlor plus mesotrione, metolachlor plus
trifloxysulfuron(0.008 kg/ha), metolachlor plus rimsulfuron (0.03 kg/ha), and an
untreated control. Herbicide treatments were applied over top two-year old Fraser fir
(Abies fraseri) and eastern white pine (Pinus strobus) in mid-June of 2004 and 2005.
Weeds present included common ragweed (Ambrosia artemisiifolia), common
lambsquarters (Chenopodium album), large crabgrass (Digitaria sanguinalis), and
carpetweed (Mollugo verticillata). Crop injury and weed control were visually rated on a
0-100% scale, with 0% equal to no crop injury or no weed control and 100% equal to
complete crop death or weed control. Visual ratings were made monthly for four
months after treatments. Tree height measurements were collected at the end of each
growing season. Weed control was similar in all treatments including MeBr, except
granular oxadiazon and metolachlor plus rimsulfuron which failed to control large
crabgrass and carpetweed, respectively. In 2004, significant visual injury was observed
on eastern white pine, one and three months after treatments containing metolachlor
were applied, and in 2005, metolachlor and mesotrione significantly reduced eastern
white pine height. In 2005, flumioxazin, metolachlor plus trifloxysulfuron and
metolachlor plus mesotrione caused significant visual injury was seen on Fraser fir three
months after treatment; however, treatments did not significantly impact tree heights.
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