There are several species of cutworms that attack young corn seedlings, and black cutworm is the most prominent of all species to cause damage to corn. Here’s what you need to know about managing this disease, in case it shows up in your fields.
The first generation of black cutworm is the only generation to have an impact on corn production. The life cycle of the black cutworm begins with the adult moths arriving from Southern states where they overwinter.
This first generation of Black Cutworm moth flight begins in early April and continues to the end of May. The moths are attracted to and deposit eggs on growing vegetation, such as winter annual weeds, grasses and cover crops. If the moth cannot find growing vegetation, it may deposit eggs on corn crop residue. The eggs then hatch and the larva begin to feed on plants. If corn was planted and the weeds were destroyed (providing a clean seedbed), corn may be the only growing vegetation for larva to feed on. This sets up the perfect scenario for corn stand reduction by black cutworms.
Larva continue feeding until mid-June and pupate from late-May to early-June with the second generation moth emerging from the soil beginning around the first of July. The third generation adult moth emerges in mid-September.
Black cutworm feeding can reduce corn stands to less than acceptable populations and impact final yields if not dealt with quickly.
Traited seed, a seed insecticide treatment, and a soil-applied insecticide treatment typically only suppress black cutworm feeding. Rescue treatments continue to be the most reliable way to get acceptable control.
Diligent scouting on a weekly basis is a must. Concentrate your scouting efforts on areas of fields that have a weed history, high crop residue or cover crops. Cutworms are nocturnal, meaning they feed in darkness and hide under crop residue or soil during daylight hours, making them difficult to see when you’re scouting.
If you see plants with erratic leaf margins, or wilted plants, try to confirm you’re seeing cutworm feeding—search for the cutworm itself within a few inches of the corn plant base by carefully digging or removing bits of soil and crop residue. (Cutworms tend to roll up into a ball when disturbed.)
Traited corn shows variable cutworm control at best, including black cutworms and most other species of cutworms as well. That means gaining control of cutworms requires a good scouting regimen accompanied by rescue insecticide treatments when certain thresholds have been met.
When 3-4 percent of corn plants show leaf feeding and/or 1 percent of plants have been cut off, a treatment for cutworms could be needed. There are many rescue insecticides labeled for cutworm control in corn, such as those with the active ingredients bifenthrin or imidacloprid. Remember to always read and follow label use directions.
Sources: 1. https://cropwatch.unl.edu/2016/nebraska-perspective-efficacy-cry1f-bt-corn-against-wbc
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