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Some Good News for Corn Producers: Fewer Rootworms

Some Good News for Corn Producers: Fewer Rootworms
Purdue University entomologists cite several reasons for the trend.

The mighty corn rootworm may have two strikes on him in the ninth inning, but don't count him out just yet. He's an insect, and they have miraculous ways of staging comebacks. And besides, he's been in this predicament borer. All he did hen was figure out how to invade first year corn.

However, at least rootworms weren't a big deal this season. It's one bit of encouraging news for Indiana's corn farmers. Because although there may still be a decent crop on the way, too much heat, inconsistent rainfall, too much humidity, and too many diseases may take the top end out of production. Lately, the news has seemed all negative.

Not so on the rootworm front, says Christian Krupke, a Purdue Extension entomologist. He believes that Bt hybrids explain part of the reason for low corn rootworm numbers this season and in several recent seasons. Typically, a BT rootworm hybrid kills 90% of the rootworm larvae that try to feed on them.

Granular herbicides can protect the roots and crop, but didn't seem to have the population-lowering effect on rootworms that Bt corn has had so far, However, there are other factors that may be contributing to the dip in rootworm numbers in Indiana recently.

Frequent, heavy rains and saturated soils during egg hatch for the past three seasons in a row haven't done the insect population any favors, at least not for rootworms. What would be interesting would be to know what numbers would have done with the advent of more Bt rootworm corn acres if springs had been more normal.

However, Krupke provides a big word of caution to those who think they can forget about rootworms from now on. Remember this is the pest that figured out how to lay eggs in soybeans and become a pest on first-year corn, in about two-thirds of Indiana. Until then, it was primarily a pest of corn after corn. That's no longer the case, especially in hard-hit areas when the new threat first arrived, such as northwest and west-central Indiana.

Growers must continue to embrace the recommended refuge strategy so that Bt rootworm corn remains an efficient, effective tool, Krupke believes. Refuge requirements are growing more complicated as Pioneer introduces 10% refuge in a bag and Monsanto has applied for 5% refuge in a bag for SmartStax hybrids. However, the bottom line is that the refuge requirements are there for a reason.

If rootworms break through Bt control, looking back to the early 90's when they first laid eggs in soybeans, which no one thought possible at the time, won't do any good either. One leading entomologist of the day actually advised ignoring reports of the first few cases of rootworms in first year corn in Illinois, believing the problem was isolated and would go away. It didn't.

So be thankful that rootworm numbers are at low tide. But don't assume you can do anything you like without them someday making a comeback, because it could happen.

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