Production Blog

DECATUR, Ill. (DTN) -- There are years when early planted crops grow quickly enough to escape black cutworm feeding. This may not be one of those years.

Cool and wet conditions in late April and early May kept planters idled in some areas of the Midwest and slowed the growth of the crop already planted. Several states have recently issued alerts about black cutworm moths captured in pheromone traps -- an early indicator of what can come next. A migratory pest in Midwestern areas that experience winter freezes, black cutworm arrives with spring storms from southern states. Damage risk increases when the offspring (larvae) of those moths coincide with small and emerging crops.

Black cutworm is a low-down, dirty killer. It inflicts damage when farmers are in a planting-time crunch and distracted. It is also nocturnal and known to cut young plants off below the growing point during the night and drag plant parts into holes or under dirt clods to feed during the day.

Corn is more susceptible to the stand loss that cutworms dole out, but larvae can also cut soybeans below their growing point, noted University of Illinois entomologist Nick Seiter. The soybean crop's ability to compensate for stand loss makes it slightly less of a risk.

"This year we have had a relatively long period with warm enough temperatures for moth flight in Illinois, despite the cooler temperatures we've seen recently," Seiter told DTN via email. "I think this was conducive to moths arriving early, which often means higher moth numbers."

A significant flight of black cutworm is generally defined as the capture of eight or more BCW moths over a two-night period. Entomologists use historical growing degree day (GDD) data and the occurrence of significant flights to determine when larvae might start feeding on crops.

Females lay eggs on grasses, weeds and crop debris. Eggs hatch in about a week, depending on temperature. Larvae typically pass through seven instars and feed on plants for 4-5 weeks before pupating. Fully-grown larvae burrow into the soil and form an earthen cell to pupate for approximately two weeks. Late summer temperatures experienced during the pupal stage trigger the moths to migrate to southern overwintering sites. The entire life cycle takes 35-60 days, depending on temperature and food quality. Depending on the time of spring arrival and summer temperatures, black cutworm may undergo one or more generations.

"Certainly, the cooler temperatures we are seeing now could leave emerged corn in a vulnerable state for longer this year," Seiter said. Wet, late planted, or weedy fields are more susceptible, too. Larvae tend to be less active when the ground is dry, often feeding below ground to escape dry conditions.

Black cutworm larvae typically cut corn from plant emergence until it reaches the V5 stage (five leaf collars), with the most severe damage occurring when larvae reach the 4th through 7th instar stages, roughly 1/2 to 2 inches long.

NOTE SUSCEPTIBLE FIELDS

Black cutworm moths tend to lay eggs in fields that might have had heavy vegetation such as henbit, chickweed and other winter annual weeds or cover crops prior to planting.

"Winter annual weed pressure during egg lay (often followed by a herbicide that pushes the larvae to corn) is a key risk factor," Seiter noted.

He recommended scouting in areas where infestations have been found in the past or near these grassy/weedy areas. Black cutworm infestations can be scattered within a field or found throughout the field. Low areas within fields are a good place to focus on scouting, he added.

EARLY BIRDS SPOT THE WORM

Seiter said the habit of feeding at night is a survival tactic by the insect to avoid being consumed by birds.

"If you want to catch them in the act, get out early or when it is cloudy. Otherwise, you might need to do a little digging to find the actual larvae," he added.

If you miss that early or late scouting window, look for small, irregular holes in leaves that indicate early instar feeding. Wilting, leaf discoloration or missing or cut plants are indications of larger larvae at work.

Don't rely on Bt traits to completely protect your corn fields, Seiter added. While some Bt traits supply suppression of these pests, they cannot necessarily withstand a heavy infestation. See more on Bt traits and their target pests here: https://www.texasinsects.org/….

Black cutworm isn't the only cutworm species to feed on crops, but it is the most common. The Crop Protection Network estimated 2025 total corn yield losses to cutworm (black and other cutworms) in the United States at 5,358.8 (thousand bushels) (https://cropprotectionnetwork.org/…).

Iowa State has a good description of cutworm identification in a recent release: https://crops.extension.iastate.edu/….

Some states have black cutworm alert networks, however not every agricultural county may have boots on the ground. So scouting is still recommended and ahead of the predicted cutting date.

As noted in a recent Iowa State release, some cutting date predictions have already passed, so it is important to scout fields as crops emerge, especially in areas with green plants at the time of planting that could harbor cutworms. For an explanation of how predictive cutting dates are established go to: https://crops.extension.iastate.edu/….

Here are links to some state resources:

Iowa -- https://crops.extension.iastate.edu/…

Kentucky -- https://ipm.mgcafe.uky.edu/…

Ohio -- https://agcrops.osu.edu/…

Michigan -- https://www.canr.msu.edu/…

Minnesota -- https://swroc.cfans.umn.edu/…

Missouri -- http://agebb.missouri.edu/…

Wisconsin -- https://datcp.wi.gov/…

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social media platform X @PamSmithDTN

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