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Frequent information updates for agricultural audiences

Black Cutworm Moth - Intense Captures - from Mike Gray

Posted by John Fulton -

Don't be lulled into complacency when using transgenic hybrids this season and assume complete protection against intense populations of black cutworm, said University of Illinois Extension entomologist Mike Gray. A stormy April across much of Illinois has led to numerous reports of black cutworm moth captures in pheromone traps.

Moth capture data from Robert Bellm, U of I Crop Systems Extension Educator, suggests the potential exists for heavy egg-laying in fields with high densities of annual weeds. This could translate into thinning of corn stands, especially those fields that are tilled and planted late. Bellm reported the following captures: Montgomery County – eight moths captured between April 11 to 12; Madison County – 11 moths captured between April 14 to 16; and Pike County – 10 moths captured on April 18.

"By using moth capture data, we can begin to project when cutting of plants may occur within a given area of the state," Gray said. "When nine or more moths have been caught over a 2-day period, which is what we consider to be an intense capture, we use this point in time as our biofix for black cutworms and begin to project when cutting of plants may begin to occur."

The first three black cutworm instars are considered primarily leaf feeders. Once the fourth instar has been reached, cutting of plants may begin. This stage typically requires an accumulation of 312 to 364 degree days (base 50 F) beyond the intense capture date, Gray added.

"Fields most susceptible to black cutworm damage are those with flourishing winter annual weed populations," Gray said. "Black cutworm moths are attracted to these weeds upon which they lay their eggs. Curled dock and yellow rocket are very attractive egg-laying targets.

"Cornfields that match these characteristics and are tilled and planted late in the spring are most prone to economic infestations of black cutworms and should be scouted carefully. Early signs of injury include pinhole-leaf feeding," he said.

In last week's issue of the Bulletin, U of I Extension Weed Specialist Aaron Hager described the common occurrence of henbit and purple deadnettle in fields this spring.

"I urge producers to scout those fields for signs of cutworm injury after corn begins to emerge later this spring," Gray said. "Even fields that have been planted to certain Bt hybrids may be susceptible to damage when heavy infestations of black cutworms are present. Rescue treatments may still be required in some instances. Continued delays in spring tillage and planting will heighten the chances for black cutworm damage this spring."

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