BLOOMINGTON, Ill. — “Wait until next year” is a phrase often
attributed to unsuccessful sports teams, but it shouldn’t be a farmer’s pest
management approach after corn reaches maturity.
Now is a good time for root digs to get a better handle on
what happened and what could be changed next year.
“It doesn’t hurt to dig up a few plants and just see what
kind of root system we have this year,” said Tom Kelley, Syngenta’s central
Illinois agronomy service representative.
“The corn plant in central Illinois did not have to put on a
lot of roots this summer because it was sitting in a greenhouse essentially. It
had plenty of moisture, plenty of nutrients, so we don’t have a large root
system to begin with, so it doesn’t take much rootworm feeding for that root
system to be compromised.”
The Iowa rootworm rating scale is recommended to determine
the extent of larval damage on crown roots.
“That’s the zero to three rating and it’s fairly easy to do
and if you need help, you can get a hold of your seed adviser or your Syngenta
agronomist and we can show you how to scout fields,” Kelley said.
“Now is a perfect time. It’s not the easiest job, but for
August our temperatures are not normally what they are in the mid-90s. It’s not
a bad job to help make plans for the future.”
If a field has heavy insect pressure after the corn reaches
maturity, it’s too late to apply insecticide, but not to use that information to
tweak next season’s pest management.
“I call those revenge sprays,” Kelley said of applying
insecticides after brown silk. “You’re basically taking revenge against the
insect, and you cannot put a big enough dent in that population to make a
difference for next year.
“A lot of the beetles you’re seeing have probably already
laid their eggs or a getting ready to lay their eggs, so they’ve already set the
stage for next year.”
There are numerous tools available to manage pests, ranging
from seed treatment and insecticides to traits.
“Syngenta is introducing a new trait next year called
Agrisure Duracade, which is a new mode of action that we’re very excited about,”
Duracade trait expresses a unique protein — eCry3.1Ab — for
control of corn rootworm.
“It kind of gets us out of that same arena that all of the
other corn rootworm traits are operating in. It gives us something new with
higher efficacy to bring to the Midwest farmer,” Kelley said. “It breaks that
cycle of resistance with a new mode of action.”
He also offered pest management recommendations for this
year’s corn crop that was planted late and has yet to reach full
“At Syngenta, one product that we consider kind of a base
product is Warrior insecticide. That not only controls corn rootworm adults, but
it also controls earworm, European corn borer, western bean cutworm and a lot of
other insects that it does control,” he said.
“If you have a really bad infestation, a lot of people are
also tank-mixing other insecticides with Warrior to give it a quick knockdown if
they’re in that critical of a situation to get pollination. We have such a small
window on pollination we have to knockdown all those bugs that we can to get
In terms of determining at what point in the plant growth
stage it no longer is beneficial to apply a fungicide, Kelley said, brown silk
is the turning point, but a closer examination of the plant may be necessary.
“Go out and evaluate your fields. I would encourage
producers to cut that ear open. That’s really how you tell,” he said.
“Most people go by brown silk, but even with a completely
brown silk, a lot of times you’ll see several more green silks coming out. The
only reason they’re growing out green silks is because it hasn’t pollinated
“I’d encourage producers to cut the husk open with a pocket
knife and gently pull off the corn husk and shake it. It is complete pollinated
when the silks separate from the kernel.
“If you shake it and still one-third of those silks are
connected to the kernels, you’re not fully pollinated yet.”
Kelley said it wasn’t a bad year thus far for insect
pressure in corn across the 10 counties he serves between Champaign County and
“As you move west and as you move north from that area, corn
rootworm pressure does increase. I did not see the corn rootworm pressure in my
area that I was expecting this year,” he said.
“So it hasn’t been that bad. Now that’s not to say that we
don’t need to be scouting our fields and evaluating the performance of either
the trait or the traditional chemistry practice that farmer used to try to
manage corn rootworm.”
For the late-planted corn that has yet to reach maturity,
Kelley said the three-part threshold to consider for corn rootworm adult beetles
in determining a need for insecticide are whether pollination occurred, five
beetles per plant and silk-clipping within a half-inch of the ear tip.
“We have to have all three of those happening before it
warrants a spray for the control or management of corn rootworm adults,” he
“For the most part, we’re well past that, but it doesn’t
mean that we can’t go out there with our shovels and evaluate what kind of
beetle pressure we have, evaluate what kind of silk-clipping that we did have.”