Use Michigan State's Handy Bt Trait table to see which Bt traits your hybrids have: http://msuent.com/….

Cry1F never fully controlled the western bean cutworm, which was added to its label years after the trait was first marketed to target European corn borer, Smith noted.

Just a few years after WBC surfaced in Ontario in 2008, field trials showed no difference between Cry1F-traited hybrids and non-Bt hybrids, she said. The rapid development of resistance may have been sped by integrated refuge practices (known as refuge-in-a-bag), as well as heavy populations of the pest, Smith said.

"As soon as we saw pest pressure go up, [Cry1F] control went down," she said.

Growers in Indiana, Michigan and Ohio saw this exact scenario play out last year, DiFonzo said. Battles watched WBC populations rise steadily in his fields in recent years before the large population last year made clear that Cry1F was no longer working there.

SCOUTING AND TREATING

This year Battles has installed a WBC moth trap. He counts its catches daily and sends weekly moth counts to Purdue University.

With help from growers like Battles, universities have developed trapping networks that can help growers track moth numbers in their area. See one from Purdue here: http://bit.ly/…; and Michigan, which uses the Canadian Corn Pest Coalition's trapping network, here: http://bit.ly/….

In the upper Midwest, moth flights usually peak in the third and fourth week of July, DiFonzo said. Growers who had fields affected by WBC last year should be sure to scout for egg masses several times over the next two weeks, she said.

Scouting for WBC eggs is difficult and uncomfortable, Battles pointed out. The moths prefer pre-tassel fields, which allow the larvae to hatch and feed on leaf, tassel and pollen tissue before migrating down into the emerging ear as larger, more damaging caterpillars. Once in the ear, they are protected from insecticide applications, which leaves growers with a small window for treatment.

If your corn plants are at eye level or higher, DiFonzo recommends an eye shield of some type to help view upper leaves more easily. Scout at least 100 plants scattered throughout five different spots in a field. If you orient yourself so that the sun is behind the leaves you're facing, you should be able to spot the shadows of egg masses on the upper canopy as you go, DiFonzo said.

Look for coin-sized clusters of tiny, white eggs, which turn purple just before they hatch. If you spot them on 5% of your plants, it's time to spray.

Keep in mind that the 5% number is cumulative, DiFonzo added.

"That cornfield will be attractive to [WBC] moths for up to two or three weeks of scouting," she explained. "So if you spot 2% one week and 3% the next week, then you're at threshold, because the eggs from last week have hatched and the larvae are still in that field."

See a video on scouting WBC egg masses from Purdue here: http://bit.ly/…. You can also find a detailed WBC scouting and lifecycle guide from the University of Guelph here: http://bit.ly/… and Michigan State here: http://bit.ly/….

You can find a list of effective insecticides from Purdue here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/AG)

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