Frit Fly is the most common pest on sweet corn plants. The larvae burrow into the plant during June and early July at the seedling stage. Small white larvae may be seen feeding in the stem and at the bases of stems. Light yellow longitudinal stripes appear on the young leaves which eventually turn brown and disintegrate into frayed strips. The plants may be stunted and the number of cobs produced later in the season may be reduced. In severe attacks the growing point is killed and the plant dies. A second generation emerges in July and August. A third generation appears in autumn which overwinter on host plants and these emerge as adults in spring.
There are no chemicals currently available for the control of this pest. Keep the surrounding area weed free as the larvae can overwinter on grasses. Where attacks frequently occur it is best to avoid sowing in the open ground and to raise the seedlings under glass for transplanting when ready.