Never have you had more options to control insects in corn--transgenics;
seed treatments; soil and foliar insecticides; and, of course, crop
rotation. But so many choices can create confusion when evaluating which
options will best solve your bug problems.
Andy Scholting, farm manager for Mead Cattle Co. at Mead, Neb., has a
clear plan for battling corn pests on continuous corn fields harvested
primarily for silage. For corn borers, he plants YieldGard and Herculex
Bt hybrids on two-thirds of the corn acres. Scholting scouts the
remaining acres planted to conventional hybrids and applies Pounce as
needed.
Corn rootworms are a huge problem on the eastern Nebraska operation.
"It's not uncommon to have 10 to 12 rootworm beetles per plant, even
after an insecticide application," says Scholting.
Before he arrived on the farm three years ago, corn was treated with
Regent. "It just wasn't providing enough control for our heavy rootworm
infestations," explains Scholting.
He switched to Aztec 4.67 granular insecticide in the SmartBox closed
handling system. A 3.27-pound-per-acre rate costs about $16.
"Aztec is doing a good job," says Scholting. "In June you can still see
some feeding on the roots, but it's not causing a yield loss and we
rarely have any goosenecking. Plus the SmartBox system provides added
handling convenience and safety."
He is hesitant to try seed treatments for corn rootworm control. "The
university data I've studied show seed treatments don't work well for
heavy rootworm pressure," he says.
Ideally, Scholting would like to plant a Bt rootworm-resistant hybrid,
but the trait is not yet available in the tall, leafy hybrids that are
ideal for silage. "We have to plant genetics first, then by traits," he
says.
Scholting's experience underscores the importance of matching the insect
control to the right pest, as well as to pest pressure.
"It's important to remember that soil insecticides generally have a
broad insect-control spectrum, while some of the newer options like Bt
hybrids and seed treatments can be more narrowly focused," reminds Larry
Bledsoe, Purdue University entomologist.
"Depending on the insects in your fields, you may have to use a
combination of treatments to get the job done," he adds.
Corn rootworm. You could almost hear the roar of applause from corn
farmers when YieldGard rootworm hybrids were released in 2003. The Bt
trait has lived up to its hype. However, the University of Illinois
reported that a test plot in 2004 with a YieldGard rootworm hybrid
showed root feeding (see "Dent in the Bt Armor?")
"In our trials, under heavy corn rootworm infestations transgenics
typically are at the top of the list in consistency and level of
control. (They are followed by soil insecticides and seed
treatments--Cruiser 1.25 mg of insecticide) and Poncho 1250," says
Purdue's Bledsoe.
Iowa State University trials show similar results under heavy rootworm
pressure. Jon Tollefson, ISU entomologist, says Bt hybrids have a
performance consistency of about 90%. Performance consistency for
top-ranked soil insecticides is 60 to 70%, and for seed treatments it is
about 25%.
To broaden YieldGard rootworm's control spectrum, Monsanto introduced
YieldGard Plus in 2004. The trait stack is a combination of the
company's corn rootworm resistance and European corn borer resistance.
In addition, all YieldGard rootworm and YieldGard Plus rootworm hybrids
are sold with either Poncho 250 or Cruiser seed treatment. This is to
protect seeds and seedlings from an army of secondary insects.
No matter what corn rootworm program you choose, be sure it's based on
sound crop scouting. University of Illinois entomologist Kevin Steffey
says you should use counts of rootworm beetles from the previous year on
corn and compare them to existing thresholds.
If a field is below threshold, you don't need to treat the following
year. But he recommends a Bt rootworm hybrid or soil insecticide if the
count is significantly above the threshold. And he says you should use a
seed treatment (higher dose formulation) for light to moderate numbers.
European corn borer. You can't forecast corn borer infestations. "It's a
hit-and-miss situation on whether you should pay for the protection,"
says University of Missouri entomologist Wayne Bailey.
"In Missouri, we usually see high populations of European corn borers
one out of every four years," he explains. "In other states where the
insect is more prevalent, many farmers will buy hybrids with the Bt
trait for peace of mind. Using a transgenic eliminates scouting fields
and worrying later in the season about proper and timely insecticide
application."
Bt options include YieldGard corn borer, YieldGard Plus and Herculex l.
Bailey says Herculex l is a popular option for many farmers because it
provides additional control of cutworms and fall armyworms.
Secondary insects. Secondary pests such as wireworms, white grubs and
flea beetles are a growing problem in many Corn Belt states. Cruiser and
Poncho seed treatments offer good control of the pests. The same is true
for many of the soil insecticides.
Check labels carefully. Of the Bt traits, only Herculex l is labeled for
control of both cutworms and fall armyworms.
"For any corn-insect control, your regimen should be a program that
provides the best economical performance and takes into account your
risk level," emphasizes Bledsoe. "Insecticides and transgenics are not
substitutes for good scouting and knowing field history."