European corn borer

About

A pale pinkish or grayish caterpillar up to about an inch long, with a dark brown head and small round spots on each segment, that tunnels into corn and peppers. It reached Massachusetts in 1917 and spread across most of the eastern U.S. to the Rocky Mountains, though widespread Bt field corn has made it much scarcer.

Spotting it

Damage

In sweet corn the older caterpillars bore into stalks and ears and chew the tips and kernels; tunneled stalks can break or fall over. In peppers they enter near the stem and feed on the seed core, and pinhole entrances with sawdust-like droppings are a telltale sign.

How to find it early

Scout corn weekly from the whorl stage for shot-hole feeding on the leaves, and check peppers for small holes near the cap with frass pushed out.

When

Late spring through summer; moths of the one-generation strain fly in July in New York.

Life cycle

Full-grown caterpillars spend the winter inside old stalks and stems and pupate in spring. There are usually two or three generations a year, but some northern populations have only one.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Clean up stalks Prevent

   After harvest, cut corn stalks close to the ground and till them under, shred them or remove them, since caterpillars spend the winter inside.

2. Split and destroy By hand

   Slit infested stalks and destroy the borers inside, and remove bored peppers.

3. Trichogramma wasps Natural enemies

   Tiny Trichogramma wasps parasitize corn borer eggs and are used for biological control (Cornell).

4. Bt (Bacillus thuringiensis) Natural enemies

   Spray Bt when larvae first appear, before they bore inside where sprays cannot reach them.

   Bt carries no bee warning on its label.

Garden friends that go after it

Minute pirate bugs, Spined soldier bug, Syrphid flies (hover flies, flower flies), Tachinid flies, Trichogramma wasps

Protect these helpers: skip broad sprays when they're around.

Plants it goes after

Celery, Dahlia, Green beans (snap beans), Hops, Pepper (sweet and chili), Potato, Rhubarb, Southern peas, Spinach, Sweet corn, Tomato

Pressure by region

Found across most of the eastern U.S. to the Rocky Mountains (Cornell). In Delaware, Maryland and New Jersey, moth catches fell 72 percent after Bt field corn arrived in 1996, and damage fell about 70 percent in sweet corn and 78 percent in peppers, so it is rated moderate, not high, even in its core range. NC State still lists it as a pepper pest in North Carolina. Southern, western, Alaska and Hawaii low ratings are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.