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Project Leader(s): Russell R.
Hahn, Department of Crop and Soil Sciences
Cooperator(s): None
Type of grant: Pheremones; biorationale;
microbiale; conventional pesticides
Project location(s): Findings
might be applied throughout the Northeast.
Abstract: Since Roundup (glyphosate)
herbicide was introduced in the mid-1970's, it has become the most widely
used herbicide in the world. Until recently, most of this use was as
Abetween crop applications@. The introduction of Roundup Ready soybeans
and corn in 1996 and 1998 respectively has drastically changed the way
this herbicide is used. Prior to this new technology, Roundup was used
in combination with other weed management practices, including herbicides
with different modes-of-action. With Roundup Ready crops, the temptation,
and in many cases, the recommendation will be to use this non-selective
herbicide alone in some cropping systems. The development of glyphosate-resistant
weed populations has been limited compared to resistance problems with
other classes of herbicides. Only four species have developed in glyphosate-resistant
populations after 26 years of glyphosate use. As glyphosate becomes
more widely used than in the past, and with the possibility of multiple
applications within a single growing season, selection pressure for
developing glyphosate-resistant weed populations will increase. There
is little evidence to date that residual herbicides are needed for Roundup
Ready soybean or corn weed control programs in New York, so the temptation
for growers will be to use Roundup alone. Preliminary results from 1999
showed that 1/4X and 1/2X rates of Roundup Ultra in combinations with
a 1/2X rate of Scorpion III (a mixture of flumetsulam, clopyralid, and
2,4-D) provided excellent control of annual weeds, including velvetleaf
which is not always well controlled with Roundup alone.
Field experiments were conducted in
2000 and 2001 at Aurora and Mt. Morris, NY to determine the efficacy
of reduced (1/4X and 1/2X) rates of Roundup Ultra in combinations with
1/2X rates of tank-mix partners in Roundup Ready7 corn. Roundup Ultra
at 0.5 and 1 pt/A was applied early and mid-postemergence (EPO and MPO)
in combinations with 1/2X rates of AAtrex, 2,4-D, Clarity, Hornet, and
Scorpion III. Each experiment also included EPO and MPO applications
of 2 pt/A of Roundup Ultra alone, a preemergence (PRE) standard treatment
of 1.5 qt/A of Bicep Lite II Magnum plus 3.6 pt/A of Prowl, and an untreated
check.
There were no differences between the
average yield of the EPO and MPO applications in any of the four experiments
and the average yield of all Roundup Ultra applications was not different
from those of the PRE standard. At Aurora, the average yield of all
Roundup Ultra treatments was 128 and 140 bu/A in 2000 and 2001 respectively
compared with 130 and 147 bu/A for the PRE standard. At Mt. Morris,
the average yield of all Roundup Ultra treatments was 176 and 185 bu/A
in 2000 and 2001 respectively compared with 188 and 190 bu/A for the
PRE standard. Weed control and corn yields were affected by herbicide
treatments in some instances. At Aurora in 2001, control of all species
was good to excellent with the reduced rate combinations except for
common lambsquarters control. EPO and MPO applications of 0.5 pt/A of
Roundup Ultra plus 1 oz/A of Hornet controlled only 63 and 73% of the
lambsquarters respectively compared with an average of 96% with the
other reduced rate combinations. The average yield for this combination
was 126 bu/A compared with 143 bu/A for the other reduced rate combinations.
At Mt. Morris, the dominant weeds were redroot pigweed and common lambsquarters
in 2000. Pigweed control was good to excellent with all treatments but
lambsquarters control was reduced with application of 0.5 pt/A of Roundup
Ultra plus 1 oz/A of Hornet. The EPO and MPO applications of this combination
controlled 86 and 80% of the lambsquarters respectively compared with
an average of 98% with the other reduced rate combinations. Reduced
lambsquarters control did not result in yield reductions at this location.
In 2001 the dominant weeds were velvetleaf and redroot pigweed. Velvetleaf
control was 82% with the 0.5 pt/A rate of Roundup Ultra tank mixes and
93% with the 1 pt/A Roundup Ultra tank mixes. The EPO application of
0.5 pt/A of Roundup Ultra plus 1 pt/A of AAtrex only controlled 55%
of the velvetleaf. Pigweed control with 0.5 pt/A rates of Roundup Ultra
plus 1 oz/A of Hornet averaged 87% compared with 98% for 0.5 pt/A of
Roundup Ultra with the other tank mix partners. There were no differences
in yield among the herbicide treatments at Mt. Morris in 2001. These
results suggest that the 0.5 pt/A rate of Roundup Ultra may not be reliable
in all situations and that Hornet may not be a reliable tank mix partner
for common lambsquarters control. On the other hand, the 1 pt/A (1/2X)
rate of Roundup Ultra in combinations with 1/2X rate of AAtrex, 2,4-D,
Clarity, and Scorpion III did provide control of a broad spectrum of
annual grass and broadleaf weeds. Yields of these reduced-rate combinations
did not differ from those of the PRE standard and each combination involved
herbicides with two or three different modes-of-action. Such combinations
would delay/prevent the development of Roundup resistant weed populations.
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