What Farmers Still Need to Know About Black Cutworm in Seedling Corn

The Agronomy Angle with The Short Bald Agronomist (Matt Montgomery, Beck’s)

A Pest Worth Remembering

Black cutworm is an easily forgotten pest for many farmers. After all, we have traits and seed treatments to help keep it in check. Occasionally though, especially in weedy spring fields, the pest can bypass traits and treatment putting the young crop at risk. Let’s spend a little time getting familiar with this once more frequent pest.

Spring Migration Brings Black Cutworm Back

Black cutworm does not winter in Illinois. Instead, the adult moths overwinter along the Gulf Coast. As spring storms work their way through Illinois, those storm fronts carry adult black cutworm moths back into the state. This annual spring migration eventually leads to young cutworms being reintroduced into area fields.

Nighttime Behavior and Life Cycle

Adult moths mate and lay eggs, at night, on the lower portions of many different plants including chickweed and curly dock. The resulting black or gray colored larvae (cutworms) also feed at night and rest during the day, curled up in a ball just beneath the soil surface or just under soil clods. 

How Cutworms Damage Corn

The pest is, of course, given its name because larvae often chew into corn seedlings, clipping those seedlings below the growing point. They can thus reduce stand which can translate into a replant scenario. 

Field Conditions That Increase Risk

Infestations of cutworm are favored by several factors. First, black cutworms are more likely to appear in late-planted corn fields. Weed infestations are more likely in delayed corn, and cutworm moths like fields with plenty of "options" when depositing eggs. In a similar fashion, broadleaf weed infestations, reduced tillage, and corn following soybeans also favor egg laying by cutworm moths and thus increase the potential for damage from the pest. The presence of substantial spring weed pressure can provide larvae a non-traited and non-treated food source, allowing larvae to reach large sizes. Larger larvae then move over to and feed upon the corn crop, inflicting substantial damage before traits and treatment kill them off.

The Threat Still Exists, Although Diminished, Today

The above scenarios mean that cutworm injury potential has not been entirely eliminated. While the potential for injury has been slashed over the past 25 years, occasional issues can still arise and growers should still watch out for cutworm issues.

Trap Monitoring vs. Scouting

Adult moth trapping can be used to track the overall movement of this pest, but trapping only provides a broad view of overall regional pressure. Scouting is still a critical need. Producers should scout corn weekly, for the first month of the young corn plant’s life. After about a month, the size of the corn plant outpaces the pest’s ability to reduce stand and scouting priority shifts to other pests.

When Rescue Treatments Make Sense

Rescue treatments are warranted when larvae have clipped around 3% of seedlings, and growers will want to consult their agronomist because a look-a-like, non-stand-reducing larva can appear in our area as well. Correct identification will make the difference between wasted dollars and dollars well spent.