Overton, Texas
April 5, 2004
Texas Agricultural Experiment
Station scientists here recently evaluated several lines of new,
transgenic alfalfa that are tolerant to the widely used, broad
spectrum herbicide glyphosate, the active ingredient in Roundup.
"This technology, similar to that used in Roundup Ready corn,
soybean, canola, and cotton, is proving effective in overcoming
difficult-to-control weeds in alfalfa.," said Dr. Vincent Haby,
Experiment Station soils scientist based at the Texas A&M
University System Agricultural Research and Extension Center at
Overton.
For the last decade, Haby has been working to make alfalfa a
viable crop for the acid soil conditions of East Texas. Haby's
work has shown alfalfa could yield a return on investment as
high as $300 per acre, higher than practically any other
agronomic crop in East Texas.
The largest cost of producing alfalfa is in its establishment,
and the gradual thinning and invasion of stands by weeds and
grasses can reduce stand life to four or five years. A
combination of herbicides may be required for control.
The genetic modification of alfalfa makes it tolerant to the
glyphosate in Roundup, potentially making weed and grass control
simpler and cheaper.
Haby's work is in its third year. Under a cooperative agreement
with Monsanto Chemical Company, the developer of the Roundup
Ready technology, Haby and research associate Allen Leonard
first tested 17 varieties, recording yield and other
characteristics.
From Haby and Leonard's data, as well as that from other
researchers around the country, Monsanto selected several
promising lines. Last year, the research team performed
tolerance level tests on a single line. The idea was to examine
in detail how different rates and number of Roundup applications
would control weeds without any damaging effect on the growing
alfalfa. This year, the tests are specifically targeting control
of bermudagrass in alfalfa stands.
In East Texas, it's not just broadleaf weeds that threaten an
alfalfa stand, it's also grasses such ryegrass and encroaching
bermudagrass. There's some question whether glyphosate will kill
bermudagrass with any reliability at the proposed labeled rates
for weed control in Roundup Ready Alfalfa.. And the proposed
labeled rates are not likely to be increased because residual
levels of glyphosate cannot be allowed to exceed those set by
the EPA.
Under current law, genetically-modified crops are subject to
strict review by several federal agencies. The U.S. Department
of Agriculture oversees seed shipping and field testing. The
U.S. Food and Drug Administration evaluates food and animal feed
safety issues. The Environmental Protection Agency establishes,
among other things, residue tolerances for food and feed crop
commodities.
In the case of the new alfalfas, EPA has established a level for
residual glyphosate in hay. To avoid any problem with residuals,
the EPA labeled rates are no more than 1.5 lb acid equivalent in
a single application per harvest, and no more than four such
applications during a growing season.
"According to Monsanto, residue data currently under review at
EPA indicate that glyphosate residues in Roundup Ready alfalfa
made into hay following the proposed maximum application rates
would not exceed the established tolerance," Haby said.
In response to these issues, Haby and Leonard are trying various
timings of Roundup with an eye on bermudagrass control. They are
also testing another grass herbicide, Select, by itself and in
conjunction with Roundup. In another strategy, they are
examining the effect of adding 2 percent ammonium sulfate
fertilizer to increase herbicide activity. It's a proven
technique, but the question is whether the boost of control will
be enough to kill the bermudagrass.
Timing of the application may also make a difference.
If the herbicide application is made too soon after a harvest,
the bermudagrass won't have enough leaf area to take up the
herbicide systemically. If the application is made too late, the
alfalfa will form a canopy and shade the bermudagrass from the
spray, Leonard explained.
Results from the current tests should be available early next
year, but it's likely to be several years before glyphosate
tolerant alfalfas reach the marketplace, Haby said.
" Before this technology is released, test results must undergo
an extensive regulatory review," he said. |