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.

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. 1. 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.

Source: Estes, K. “Black cutworm feeding possible in coming weeks.” Department of Crop Sciences, University of Illinois, May 17, 2023.

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About the Author: Kelly Estes

Kelly is an entomologist at the University of Illinois where her role is the State Survey Coordinator of the Cooperative Agriculture Pest Survey (CAPS) program. She coordinate surveys for invasive insects, pathogens and weeds that are a threat to Illinois’ agriculture, forestry, horticulture, and the environment. She works work with the Illinois Department of Agriculture and USDA-APHIS-PPQ along with industry stakeholders, University of Illinois Extension, and many others. In addition to coordinating surveys and managing the data associated with them, she helps develop public information and educational material for these invasive pests.

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