Life History and Damage

The life cycle of the European corn borer on sweet corn is very similar to that on field corn. Large populations of larvae usually result from significant egg laying occurring between early whorl and fresh silk stages of sweet corn development. The most vulnerable time for ear infestations is when egg laying occurs during late tassel to silking. Late-planted sweet corn and long-season varieties usually have heavier infestations of larvae than do early-planted, short-season varieties. The late summer populations of larvae are generally higher in sweet corn than in field corn under similar conditions. Nearly all varieties of sweet corn are susceptible to European corn borer. Little has been done to develop sweet corn resistance to this pest as compared to efforts in field corn.

Figure 38. European corn borer larva feeding on the side kernels and ear tip of sweet corn.

The primary cause of damage by European corn borer in sweet corn is direct feeding on the ears. This affects marketability of the corn for fresh market or processing. Most ear damage occurs from larval feeding on the kernels in the ear tip or along the side of the ear (Figure 38). Many processors believe the European corn borer is a more serious problem than the corn earworm (photo), Helicoverpa zea, because of the difficulty in detecting the infested kernels on the side of the ear and, consequently, the increased chance of contamination in the final processed product. Additional damage occurs from feeding on the leaves and boring in the butt of the ear, shank, and stalk. This may reduce yield through physiological effects on the sweet corn plant.

Ear damage tolerance levels vary, depending on the processor or fresh market outlet. Some processors can tolerate up to 20 percent ears with tip damage and up to 5 percent with side kernel damage before the quality of the final food product is affected. This also depends on whether the corn will be processed as cut corn, cream style, or corn-on-the-cob. The latter has the most strict tolerance limits. Most processors prefer little or no damage and, in some cases, provide a bonus for insect-free corn. Fresh market outlets generally require less ear damage than processors.