Corn Earworm

Trichogramma pretiosum egg parasitoid wasps attack corn earworm eggs before they hatch — release weekly during silking at 50,000-200,000 per acre or equivalent garden scale. These are available from insectaries and are one of the most cost-effective biological controls for caterpillar pests. Tachinid flies parasitize larvae. Support both by planting dill, fennel, and sweet alyssum nearby. Predatory stink bugs (Podisus maculiventris) eat earworm larvae — they are beneficial, distinguish them from pest stink bugs by their pointed "shoulders" and predatory posture.

Corn earworm moths lay single eggs on corn silks — the larvae burrow down the silk channel into the ear where no spray can reach them. The window to act is narrow: from silk emergence to when larvae tunnel in (about 3-5 days). Pheromone traps monitor moth flight — when catches peak, silk protection must begin immediately. Tight-husked corn varieties provide some physical protection. In the home garden, applying a few drops of mineral oil or vegetable oil to the silk tip after pollination is complete blocks larval entry effectively.

Plant corn in a tight planting window rather than staggered plantings — extended silk periods extend your exposure to multiple moth flights. Destroy crop residue immediately after harvest — pupae overwinter in soil under corn debris. Interplant with diverse flowering plants to support parasitoid populations. Corn earworm also attacks tomatoes, peppers, and beans — monitor all these plants when corn moths are flying.

For home garden corn, apply mineral oil with a dropper to silk tips after 80% of silks have browned (indicating pollination is complete) — this blocks larval entry without affecting pollination. Individual ear bags applied after pollination physically exclude moths. Hand-pick larvae from tomatoes and peppers where they bore into fruit — look for entry holes and frass at the stem end.

Bacillus thuringiensis kurstaki (Bt) sprayed on silks every 2-3 days during silk emergence kills newly hatched larvae before they tunnel in — this is the critical window. Once larvae are inside the ear, no spray reaches them. Spinosad provides stronger knockdown and slightly longer residual — apply at dusk to minimize bee exposure. Neem oil deters egg-laying when applied to silks and foliage but has minimal effect on larvae already tunneling.