What's Bugging Your Corn?

What's Bugging Your Corn?

Keep an eye out for high-cost corn crawlies - slugs, black cutworms and rootworms. They quickly get expensive, even with seed-applied insecticides and Bt corn.

As of May 15, except for a few local outbreaks, all was fairly quiet on the Northeast's invasive bug front. That was the word from John Tooker, Extension entomologist at Penn State University. But that can change quickly, he adds.

A week ago in Indiana, it did change rapidly as record numbers of black cutworm moths descended on the state in a round of storms originating in southern states. Don't be lulled into a false sense of security with seed-applied insecticides or Bt corn, warns Purdue Entomologist John Obermeyer. "These technologies don't stand up to severe infestations."

OKAY, WHERE'D IT GO? As this field shows where corn hybrids were switched, not all Bt hybrids offer the same insect protection.

The key to successfully controlling black cutworms is to scout early and often and to apply insecticides when larvae are small. Large larvae are difficult to control. For more details on black cutworm management options, click on Penn State's fact sheet.

Act quickly on slimy slugs

With recent wet conditions across much of the Northeast, no-till growers and minimum-till producers with heavy residues should have slugs in mind, cautions Tooker. "These slimy mollusks can quickly decimate newly sprouted fields. Be sure to scout low-lying fields or those with heavy residue."

If rescue treatments are warranted, act quickly, he adds. Click on this fact sheet for details.

Keep WCRW BT resistance in mind

In Illinois and Indiana, western corn rootworm larvae began hatching about three to four weeks in advance of their usual timing. That's the earliest rootworms have hatched in 35 years, notes Tooker.

As a result, rootworms may impose more feeding pressure on younger corn plants than usual. Adults are expected to be active much earlier as well.

For much of Pennsylvania, corn rootworms aren't a threat because growers rotate their crops fields annually, and rootworm populations can't establish here unless corn is grown continuously. However, where continuous corn is grown, there's potential for development western rootworm resistance to some Bt corn hybrids.

Pennsylvania and for this acreage, it is worth reminding folks of the populations of western corn rootworm from the Midwest that were confirmed last year to be resistant to some Bt corn varieties targeting rootworms. Field-evolved resistance to the Cry3Bb1 toxin was expressed in some Bt transgenic varieties.

If you see unexpected damage from rootworms in continuous corn acreage, please contact Tooker directly at [email protected].

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