Entomologist advises farmers on the arrival of black cutworm
Black cutworm
Black cutworm (Photo credit: John Obermeyer)

Black cutworm has arrived in Indiana, meaning farmers will need to monitor their fields as corn is planted and starts to emerge, a Purdue Extension entomologist says.

Pheromone trapping cooperators statewide reported a significant number of black cutworm moth captures during recent warm spells. The pest overwinters in warmer states, mostly surrounding the Gulf of Mexico, but migrates north starting in late February until June.

"The pleasant weather that blew in from the southwestern portions of the country also brought a mass of moths," said Christian Krupke, who specializes in field-crop pests.

While a majority of the early-arriving black cutworm moths and their eggs likely perished, Krupke said more are arriving with incoming storm systems; as happens every year around this time.

Purdue Extension entomologists track male black cutworm moths to gauge the threat to the state’s corn crops using traps baited with synthetic versions of female-produced pheromones. While the traps give some sense of pest populations, they're limited because they don't catch female moths, which lay the eggs that hatch the larvae that damage crops.

Black cutworm is known for sporadic outbreak patterns. Because of that, Krupke said the economic approach to management is to watch nearby pheromone trap counts updated weekly in Purdue Extension's Pest and Crop Newsletter (http://extension.entm.purdue.edu/pestcrop/index.html); scout cornfields prioritizing fields near locations with high catches; and then determine infestations and damage levels and use a foliar insecticide treatment if needed.

"Producers using insecticide-treated seed may have a false sense of security concerning black cutworm control," Krupke said. "The systemic activity of these newer insecticides during the seedling stage should help suppress the smallest larvae feeding on plants. However, this protection is short-lived and does little for control of larger caterpillars that may have moved over to corn after feeding on winter annual weeds.

"A large degree of overlap between dead and dying annual weeds in fields and young corn plants increases the chances of black cutworm damage."

Another issue is that when temperatures are cool, seedling growth slows, which also slows uptake of insecticides. Without the insecticide uptake necessary to protect them, seedlings become more vulnerable.

Black cutworm moths are brown with dark scales and dagger-shaped markings on their forewings. The larvae are light gray to black, greasy in appearance and vary in size from an eighth of an inch to 2 inches. They earn their name because larvae can destroy young corn plants by cutting through their stalks.

But once black cutworm feeding gets to the point of cutting, Krupke farmers have a hard time controlling the pest.

"Once the cutting stage is reached, control is difficult," he said. "Notching of leaves is the characteristic feeding of younger caterpillars and this is the stage that should be controlled with insecticide sprays when necessary."

More information about corn insect treatments are available in Purdue Extension's Corn Insect Control Recommendations - 2014 publication, available for free download here: http://www.extension.entm.purdue.edu/publications/E-219.pdf.

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