Golden Valley, Minnesota
February 27, 2008
More farmers are relying on Bt
corn to stop rootworms before they cause yield-robbing damage.
Rootworms are most vulnerable to Bt toxins during the first
instar, when larvae are under 1/8 inch long. But what would
happen if insects fed on something else during this stage? Say
they chewed on weeds, for instance, and grew large enough to
withstand Bt toxins?
A USDA-ARS research team at the University of Missouri tested
just such a scenario in greenhouse studies. They found that
western corn rootworms don’t like johnsongrass roots, but they
will munch on foxtail roots.
Now the researchers are tracking isotopes to determine just how
much of the larvae’s diet comes from corn roots versus weed
roots. Results may be of particular interest to growers who
plant Bt corn for rootworm control and employ total-post
herbicide programs.
Von Kaster, entomologist with Syngenta Seeds, says field trials
with its Agrisure® RW corn rootworm trait have demonstrated
excellent rootworm control and no apparent correlation between
trait performance and early-season weed infestation.
Nevertheless, Kaster says we should not underestimate corn
rootworm’s ability to overcome control measures.
“We’ve already seen rootworms develop resistance to insecticides
and crop rotation,” he says. “It’s an incredibly adaptable and
damaging pest, so it’s in our best interest to know as much as
we can about its biology and behavior to develop measures like
planting of rootworm refuges to protect highly effective Bt
technologies.”
In the USDA greenhouse studies, researchers measured adult
beetle emergence from larvae feeding on Bt corn roots, weed
roots and a combination of the two. Glyphosate herbicide was
applied to the combination treatment to mimic a total-post weed
control program. More beetles came from the combination than
from either alone. In related studies, larval survivorship was
relatively high in large crabgrass, giant foxtail, witchgrass,
woolly cupgrass and green foxtail.
While these findings clearly demonstrate the potential for
rootworm larvae to survive the first instar on grassy weeds, the
effect on rootworm control in field trials has been minimal.
“At this point, it looks like the main reason for early-season
weed control in corn is still to curb yield-robbing competition
for nutrients and moisture,” says Kaster.
The AgriEdge® Corn program from Syngenta encourages early-season
weed control in Bt corn fields through incentives to growers who
plant hybrids with the Agrisure RW trait. Through its refuge
reward, the AgriEdge program also makes it more profitable for
growers to manage their refuge acreage with Force® 3G soil
insecticide.
More information on the University of Missouri research can be
found at www.ars.usda.gov. For more information about the
AgriEdge programs, go to
www.agriedge.com.
Syngenta is a world-leading agribusiness committed to
sustainable agriculture through innovative research and
technology. The company is a leader in crop protection, and
ranks third in the high-value commercial seeds market. Sales in
2007 were approximately $9.2 billion. Syngenta employs over
21,000 people in more than 90 countries. Syngenta is listed on
the Swiss stock exchange (SYNN) and in New York (SYT). Further
information is available at
www.syngenta.com.
Important: Always read and follow all bag tag, grower agreement
and label instructions before buying and using these products.
FORCE® 3G IS A RESTRICTED-USE PESTICIDE.
Agrisure® AgriEdge® and Force® are registered trademarks of a
Syngenta Group Company. |
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