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The Bulletin

Black Cutworm Feeding Possible Throughout Illinois

Kelly Estes

Department of Crop Sciences
University of Illinois

May 13, 2024
Recommended citation format: Estes, K., . "Black Cutworm Feeding Possible Throughout Illinois." Department of Crop Sciences, University of Illinois at Urbana-Champaign, May 13, 2024. Permalink
Fig. 1. Projected cutting dates based on significant moth flights.

Black cutworms have been observed in traps across the state for the past couple of weeks. Several counties have reported significant moth flights (9 or more moths over a 2-night span). We can use the date of the significant flight to predict potential cutting dates based on degree day predictions.

Based on trap catches in late April and May, many counties in Illinois may start observing feeding, including cutting, as early as this week (Figure 1). This spring we have experienced sustained flights throughout the spring. That, combined with the wet weather and prolonged planting period, we can expect to also see prolonged periods of potential feeding with multiple life stages of cutworm. It is also important to note that feeding may still be possible in counties that did not record significant moth flights.

For more complete information about the biology, life cycle, and management of black cutworms, a fact sheet is available from the Department of Crop Sciences, UIUC. Provided below is a brief overview of some key life cycle and management facts concerning black cutworms.

Black cutworm moths are strong migratory insects with northward flights commonly observed from Gulf States into the Midwest from March through May.

Moths are attracted to fields heavily infested with weeds such as chickweed, shepherd’s purse, peppergrass, and yellow rocket. Late tillage and planting tends to increase the susceptibility of fields to black cutworm infestations. Cutting of corn plants begins when larvae reach the 4th instar — with a single cutworm cutting an average of 3 to 4 plants during its larval development. Cutting tends to occur most often during nights or on dark overcast days.

Fig. 2 . Black cutworm larvae uncovered at the base of a cut plant. Photo: Robert Bellm

Fields at greatest risk to cutting and economic damage are in the 1-to-4 leaf stage of plant development. An early warning sign of potential economic damage includes small pinhole feeding injury in leaves (caused by the first 3 instars). Producers are encouraged to look for early signs of leaf feeding as a potential indicator of cutting, rather than waiting for cutting to take place. Don’t assume that all Bt hybrids offer the same level of cutworm protection. Plants in the 1- to 4-leaf stage are most susceptible to cutting.

Cutting of plants earlier than these projected cutting dates is possible — localized intense flights may have occurred and were not picked up by our volunteers. A nominal threshold of 3% cutting of plants has traditionally been used as a point at which growers should consider a rescue treatment.

Not all Bt hybrids offer adequate protection against black cutworm damage. Growers should consult the Handy Bt Trait table prepared by Dr. Chris DiFonzo at Michigan State University to determine the level of protection provided by their chosen Bt hybrid.

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