West Lafayette, Indiana
April 14, 2009
Roundup Ready crops have made weed
control much easier for farmers, but a new study shows their
reliance on the technology may be weakening the herbicide's
ability to control weeds.
Bill Johnson, a Purdue
University associate professor of weed science, said farmers
who plant Roundup Ready crops and spray Roundup or
glyphosate-based herbicides almost exclusively are finding that
weeds have developed resistance. It is only a matter of time,
Johnson said, before there are so many resistant weeds that the
use of glyphosate products would become much less effective in
some places.
"We have weeds that have developed resistance, including giant
ragweed, which is one of the weeds that drove the adoption of
Roundup," Johnson said. "It's a pretty major issue in the
Eastern Corn Belt. That weed can cause up to 100 percent yield
loss."
Johnson was part of a team, including Steve Weller, a Purdue
professor of horticulture and landscape architecture, that
surveyed farmers in Indiana, Illinois, Iowa, Mississippi,
Nebraska and North Carolina about their views on the ability of
Roundup Ready crops to help control problematic weeds. A paper
on the survey was published in the most recent edition of the
journal Weed Technology. Researchers from Iowa State University,
Mississippi State University, North Carolina State University,
the University of Nebraska and Southern Illinois University
Carbondale also contributed.
Roundup Ready crops are resistant to glyphosate, the active
ingredient in Roundup. So, if a farm uses Roundup Ready crops,
the herbicide can be sprayed on crops to kill weeds without
damaging those crops.
Johnson said the problem has become farmers' overreliance on
Roundup and Roundup Ready crops. Those who saw the most benefit
from using Roundup, according to the survey, rotated between
types of crops and those that were Roundup Ready and
conventional crop varieties.
Johnson said this shows that subjecting weeds to different
herbicides is important to keeping them from developing
resistance to any particular herbicide.
"Farmers do not think resistance is a problem until they
actually have it," Johnson said. "And they think the chemical
companies can turn on the spigots and produce a new herbicide
whenever they want. The problem is, since Roundup is so
effective, there's not been any money for new herbicide
discovery."
Johnson said farmers should treat Roundup and Roundup Ready
crops as an investment and work to protect the technology.
Rotating crops consistently and using various herbicides will
slow the development of glyphosate-resistant weeds.
"Go after weeds with two different herbicides. That's the best
short-term solution," Johnson said. "We want to minimize the
number of weeds resistant to Roundup. To do that, you want to
minimize the exposure that a weed population has to Roundup. If
you diversify a little bit, you'll extend the life of the
technology."
Monsanto, the maker of Roundup, funded the survey. Johnson said
the next step is studying the differences among management
strategies in grower fields to see which will slow the build-up
of glyphosate resistance.
U.S. Grower Views on Problematic Weeds and
Changes in Weed Pressure in Glyphosate-Resistant
Corn, Cotton, and Soybean Cropping Systems
Greg R. Kruger, William G. Johnson, Stephen C.
Weller, Micheal D. K. Owen, David R. Shaw, John W.
Wilcut, David L. Jordan, Robert G. Wilson, Mark L.
Bernards, and Bryan G. Young
ABSTRACT
Corn and soybean growers in Illinois, Indiana, Iowa,
Mississippi, Nebraska, and North Carolina, as well
as cotton growers in Mississippi and North Carolina,
were surveyed about their views on changes in
problematic weeds and weed pressure in cropping
systems based on a glyphosate-resistant (GR) crop.
No growers using a GR cropping system for more than
5 yr reported heavy weed pressure. Over all cropping
systems investigated (continuous GR soybean,
continuous GR cotton, GR corn/GR soybean, GR
soybean/non-GR crop, and GR corn/non-GR crop), 0 to
7% of survey respondents reported greater weed
pressure after implementing rotations using GR
crops, whereas 31 to 57% felt weed pressure was
similar and 36 to 70% indicated that weed pressure
was less. Pigweed, morningglory, johnsongrass,
ragweed, foxtail, and velvetleaf were mentioned as
their most problematic weeds, depending on the state
and cropping system. Systems using GR crops improved
weed management compared with the technologies used
before the adoption of GR crops. However, the
long-term success of managing problematic weeds in
GR cropping systems will require the development of
multifaceted integrated weed management programs
that include glyphosate as well as other weed
management tactics. |
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