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Black Cutworm Moths Showing Up In Big Numbers

You may not have a single seed in the ground yet this spring, and already there's a pest you may need to watch for -  as soon your corn crop pops out of the ground.

Black cutworm moths have been trapped in spots around the mid-South and Corn Belt this spring, a sign that the migratory pest (more common later on during the spring and early summer) could be a bigger-than-normal problem for corn farmers this year.

Traps in Iowa, Illinois, Indiana, and Kentucky, for example, have snagged numbers of moths high enough earlier this month to show when and where exactly scouting for the larvae should begin, entomologists say.

"Seeing significant moth captures in early and mid-April is unusual and could indicate a more frequent incidence of vegetative crop injury compared to other years. There have been reports of black cutworm moth trap catches from other states besides Iowa, including Minnesota, Illinois, Indiana, Missouri, and Kentucky," according to a report from Iowa State University crop and insect specialists Erin Hodgson, Adam Sisson, and Laura Jesse. "In some places, such as Indiana, peak flights are being reported. A peak flight is a specific number of moths caught in a trap that signals when to begin adding up temperature data to figure out when to scout for larvae."

In Illinois, traps in Champaign, Fayette, Logan, Lee, Macon, Macoupin, and Madison counties have snagged moths as early as the first week of April. That's got Mike Gray, University of Illinois Extension entomologist, cautioning farmers to stay on top of scouting for the pest even with the smallest corn plants.

"This distribution of captures suggests that black cutworm moth flights have likely taken place throughout Illinois, and growers are encouraged to remain vigilant for early signs of leaf feeding when corn seedlings begin to emerge. Strong winds from the south are undoubtedly bringing many black cutworm moths into Illinois, and weedy fields will be prime targets for egg laying by this species," Gray says, adding fields with a lot of weed pressures, specifically from things like chickweed, shepherd's purse, peppergrass, and yellow rocket, are typically more susceptible to infection from egg-laying moths.

The larvae inflict the most cutting damage to plants in the 1- to 4-leaf stages, Gray adds. When scouting, look for "small pinhole feeding injury." That's a sign that you could be looking at potential economic damage, usually about 3% cutting of plants, or "the point at which growers should consider a rescue treatment," according to a University of Illinois Extension report.

If you've yet to plant corn, don't worry about the bug just yet, adds Purdue University entomologist Christian Krupke. Though there are some options for preplant treatments, it's best to wait and see what kind of damage you could be facing before you spray. Make sure you're scouting; don't lean on seed-applied insecticides, as they'll likely lose efficacy before black cutworm larvae are ready to cut into your crop.

"Because of the sporadic outbreak nature of this pest, the tried, true, and economic approach to black cutworm management is to scout fields, determine infestation and damage levels, and use a rescue treatment, if needed. Foliar insecticides are effective, especially when applied early. Producers using insecticide-treated seed may have a false sense of security concerning black cutworm control. The systemic activity of these insecticides during the seedling stage should help suppress small larvae feeding on plants," Krupke says in a university report. "Larger larvae, as with all insects, are more difficult to kill. Coupled with the fact that there is less insecticide in plant tissues at this time, efficacy declines as the spring wears on. The black cutworm flight and egg-laying period spans several weeks, and green or weedy fields may attract egg-laying moths over multiple flights. These fields can experience significant damage and stand losses, even when treated seed is used."

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