Corn borer feeding weakens plants and slows their growth. Severely damaged plants often snap off and fall over. When peppers or mature corn ears are damaged, they are prone to rot.
Corn borers have numerous natural enemies, including wasps, lady beetles, lacewings and other common beneficial insects, so growing flowers that attract borer predators is quite effective with this pest. In a large planting of sweet corn, intercropping with buckwheat, dill and coriander can prevent corn borer problems. Pupae overwinter in corn stalks, so add them to a compost pile and make sure they're actively composting by late spring.
Spray plants with a Bt or spinosad-based insecticide near where you see damage, and be sure to cover the leaf undersides while avoiding spraying the tassels. Many beneficial insects gather corn pollen from corn tassels.