Indianapolis, Indiana
June 19, 2007
Source:
Dow AgroSciences LLC
Western bean cutworm will return
to Midwestern cornfields this summer. Exactly where and in what
numbers remains to be seen.
“It has established itself in Iowa; it will not go away,” says
Marlin Rice, extension entomologist at Iowa State University.
“It is a permanent resident of our corn now.”
While the northwest quarter of Iowa has been hardest hit by
western bean cutworm since it became a pest of Iowa in 2000,
Rice says Iowa State has documented the pest’s presence in
nearly all of the state’s 99 counties.
And with moths captured in Michigan and Ohio in 2007, it appears
western bean cutworm is continuing its march east through the
Corn Belt. Last year, significant numbers of moths were trapped
across northern Illinois and parts of southwestern Wisconsin,
meaning extension entomologists in those states are paying close
attention to the pest this year.
“Right now, I wouldn’t call it an established pest in Illinois,”
says Kevin Steffey, University of Illinois extension
entomologist, “but it will most likely be one.
“We have watched what has transpired in Iowa the last several
years and we want to see if the trend is mirrored in Illinois.
We should have expectations for ever-increasing numbers unless
something drastic happens to suppress populations.”
The theory of pest replacement — where one insect grows in
numbers and replaces a pest that has seen populations fall
dramatically — could be a reason for the growth of western bean
cutworm. In this case, European corn borer populations have
fallen dramatically with the introduction of in-plant traits.
“I’ve got a theory. I don’t know how good it is yet, but I have
to ask myself why western bean cutworm became a pest of Iowa in
2000,” Rice says. “We know it was in the state for the previous
30 years, but it was rare.
“What has changed during the years prior to 2000 that would
affect these insects, in my mind, is transgenic corn, which
decreased European corn borer populations and allowed western
bean cutworm, which is not affected by YieldGard® Corn Borer, to
expand. I have some data that supports that, but I’d hate to say
that’s the singular reason. We know the insect is affected by
disease, and maybe diseases aren’t as severe here as in other
states.”
Steffey adds: “YieldGard Corn Borer has been planted on a lot of
acres and is not effective against western bean cutworm. It’s
very effective on European corn borer and has some impact on
corn earworm, so it may have cleared out a niche for western
bean cutworm because its competitors — European corn borer and
corn earworm — are no longer as prevalent.”
In the last several years, the introduction of hybrids
containing HERCULEX® Insect Protection has provided corn
producers with a Bt trait option that protects against western
bean cutworm. Rice says they have seen HERCULEX provide 80
percent to 90 percent control of western bean cutworm.
“It will allow a little bit of ear-tip feeding, but nothing that
causes economic damage,” Rice says. “I’ve sometimes seen
identical levels of economic damage between a conventional,
non-Bt hybrid and a hybrid with the YieldGard trait.”
While it’s possible to control western bean cutworm with
insecticides, it takes diligent scouting and timely insecticide
sprays once threshold levels of western bean cutworm larvae are
identified.
“It’s not easy to control,” Rice says. “You’ve got to have an
estimate of the egg density in a field. The field has to be
scouted; you need to know when eggs are starting to hatch,
because it’s just a matter of days before they crawl from the
flag leaf down to the ear. Once they’re in the ear, they’re home
free.”
Rice adds that the fact eggs can hatch over a five-week period
adds to the complexity of scouting and controlling western bean
cutworm with insecticides.
“Scouting and application timing are the two weak links. It can
be done, but it’s not easy,” he says.
When it comes to yield losses, the standard estimate is that one
western bean cutworm larvae per plant can cause yield losses of
3.7 bu./A, but it is highly variable. Rice saw yield losses of
up to 14 bu./A last year, and Nebraska Extension has seen yield
losses ranging up to 50 percent.
“We will have a network of moth traps this summer, which should
allow us to keep a handle on populations,” Steffey says.
“However, people need to crank up their vigilance as to what the
moth flights are doing in their area, then get out and scout
their fields.”
®HERCULEX is a trademark of Dow AgroSciences LLC
®YieldGard is a registered trademark of Monsanto Company.
HERCULEX Insect Protection technology by Dow AgroSciences and
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