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Pest, Disease & Weed Timing CalendarsCorn Earworm Calendar
Corn earworm risk in sweet corn peaks around silking, and trap catches of moths tell you when to pay closest attention.
Key points
- Silking is the critical window, and trap catches show when moth pressure is rising.
- Use pheromone traps and write counts next to silking dates for each planting.
- Moth arrival can vary with weather systems, so use local alerts.
- Use your state's interval or threshold tables, and follow the label.
Why does silking set the corn earworm calendar?
Corn earworm moths lay eggs on fresh, green silks, and the hatching larvae move down the silk channel to feed on kernels at the ear tip. Once larvae are inside the husk they are hard to reach, so the weeks of silk emergence are the period when timing counts most. Penn State and Utah State extension pages describe this relationship between moth flights, egg laying on silks and ear damage.
That means two clocks run side by side: the crop clock, which is the date silks appear in each planting, and the moth clock, which is the flight recorded in traps. Your calendar tracks both.
For example, if your first planting silks in mid-season and your trap catch is rising that same week, that planting deserves the closest checks, while a later planting that has not yet silked can wait for its own turn.
How do you monitor corn earworm moths?
The standard tool is a pheromone trap, which attracts males of the species. Many extension services give guidance on trap placement, such as setting traps near the crop before silking and checking them on a regular schedule. The University of New Hampshire's fact sheet on trapping sweet corn insects explains setup and checking routines.
Record the number of moths per trap per night or per week. A rising catch as silking begins is the key signal. A low catch with steady weather suggests lower risk, though it is still worth checking silks.
- Trap placed before silking begins
- Same checking day each week, or more often when flights rise
- Lures replaced on the schedule the supplier states
- Counts written next to silking dates for each planting
How do weather and migration affect timing?
In many northern areas, corn earworm moths do not overwinter successfully and arrive from the south on weather systems in summer. That makes the timing of first flights vary from year to year, and it is why local trap networks and extension alerts are valuable. In warmer states, local populations can persist through the year.
Warm nights speed up egg laying and larval development, so late summer plantings often face more pressure than early ones in many regions.
Write the date of your first catch each year and compare. Over several seasons you will see whether first arrival in your area is early or late relative to your plantings.
What should you check on the crop itself?
Look at fresh silks for eggs, which are tiny and cream to tan, and at the ear tip for small larvae. Pull back a few husks from sample ears at the stage your extension service suggests. Check several ears in several spots, not only the edge rows.
Different plantings silk at different times. Treat each planting as its own calendar, since moth pressure can differ across the same week.
Ear tip damage is often limited to the top few inches, and many buyers tolerate it better than damage in the middle of the ear, so judge the loss against your market.
How do extension thresholds work for sweet corn?
Many state programs link the interval between treatments, if any, to the number of moths caught in traps. A low catch may permit longer intervals during silking, while a high catch shortens them. These tables differ by state and by the market you serve, so use the version your extension service publishes.
Fresh market sweet corn usually has less tolerance than corn for processing, so ask your extension office what fits your market.
What cultural and variety choices help?
Varieties with tight husk coverage past the ear tip can reduce damage in some conditions. Planting dates matter too, because planting so that silking avoids peak moth flights can lower pressure where flight patterns are known. Natural enemies such as predators and parasitic wasps provide some control of eggs and small larvae.
Field corn is damaged less in many seasons, though earworm still occurs. Scout in the same way if ear feeding has been a problem.
What does the label say?
Any insecticide used during silking must follow the label, which is the law. Pre-harvest intervals apply, pollinators such as bees collecting pollen from tassels must be protected, and applicator licensing varies by state. Resistance in this species has been documented for some products, so rely on current local advice.
Record each trap check, each silking date and any decisions made. The record becomes your best reference for next year.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.