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A few early corn insect threats

A lot of the latest weather forecasts for this summer in the Corn Belt include warmer-than-normal temperatures and the likelihood of less-than-normal precipitation. That's good news for some insect species that could damage your crops this growing season.

Already, Purdue University Extension entomologists have noted, for a couple of weeks now, an "inordinate number" of black cutworm moths in pheromone traps around Indiana. It could be the start of a year of high stress from black cutworms, making it a pest Purdue entomologist Christian Krupke warns to stay on top of this year, even now when the pest's arrival is typically not much to worry about.

"Normally we discount these early arriving moths, because they freeze out...not this year," he says. "Indiana is the new Georgia and BCW moths are loving it."

Black cutworm moths will stay away from tilled fields or those with little plant material. But, others with at least some ground cover plants, like a no-till field, for example, will be targets for those moths to lay their eggs.

"Barren fields are not appealing. Moths are particularly attracted to winter annuals, such as chickweed and mustards. But the black cutworm has a broad host range, and fields that are showing plenty of green, yellow, and purple (henbit) are at highest risk for cutworm damage. Remember, corn is one of the black cutworm’s least favorite foods, it just so happens it is the only plant remaining by the time larvae have emerged and weeds have been killed," Krupke says. "A window of weed-free ground before planting is an ideal solution."

Allowing time to pass before planting could be a challenge this year, with the "compression of field activity" on many farms with the rapid and early arrival of spring weather conditions, Krupke adds.

Even if you're putting down a burn-down herbicide before you plant, wait at least a week before you plant to ensure those weeds -- and the cutworm larvae they could be supporting -- are knocked down.

"As many producers learned last year with a black cutworm outbreak, seed-applied insecticides do not offer satisfactory control under high pressure. In addition, some varieties of Bt-traited corn do not perform well, those are cases where the label provides only 'suppression' and not 'control,'" Krupke says. "Check the fine print on the trait you are using! Weak performance (suppression) is fine under ideal environmental conditions and zero to low-moderate infestation levels. The systemic activity of the seed-applied insecticide, and/or the protein production of the Bt-corn are optimal when the corn seedling is actively growing. However, under environmental stress (i.e., cooler soils) the efficacy of these control products are greatly reduced, leaving the struggling seedling vulnerable to attack by above and below ground insect pests."

Though the black cutworms are on their way to the fields now, others, like spider mites and grasshoppers, could be a bigger problem than normal this summer, especially if the weather stays on the warm and dry side. Conditions like that are perfect for these pests, especially if there's not much major spring moisture before summer rolls around, according to Iowa State University Extension entomologist Erin Hodgson.

"The biggest problem I see with insect management this summer is if we have hot, dry weather. We didn't accumulate a lot of soil moisture this winter and so most fields are starting out dryer than normal," she says. "So if we don't get more spring moisture, fields could be drought-stressed later on when insects are really active. In hot and dry weather, I tend to think about grasshoppers and spider mites becoming problematic because they thrive in those conditions."

If you suspect these bugs may cause you problems this year, make sure you catch them early; with spider mites, for example, this requires some fairly in-depth scouting. Once you can see the damage they cause, Hodgson says it "indicates they've been feeding for a long time."

But, on the flip side, don't just treat "just in case," she adds. And, don't think a single treatment can get you by this year.

"I do think we might run into some situations of treating fields more than once, particularly if fields are treated early this year," Hodgson says. "So I recommend just treating when you need to based on a density/damage threshold rather than a 'just in case' application."

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