The Corn Earworm in Southwestern Idaho: Infestation Levels and Damage to Processing Corn and Sweet Corn Seed12

Abstract

Corn earworm damage to processing corn and sweet corn seed was determined in 2 cultivars, ‘Barbecue’ and ‘Elite’, that were silking from early July through mid-Aug. Penetration of the ear from the tip by 1, 2, 3, and 4 larvae/ear was determined for processing corn and cm2 of corn destroyed per ear for seed corn. Growing degree days (GDD), base 10° to 30°C (50°–86°F) were accumulated from Jan. 1 to silking. No significant differences were present between cultivars. Mean penetration for 1, 2, 3, or 4 larvae/ear was 4.0, 6.5, 7.3, and 7.6 cm, respectively. However, penetration by one larva/ear decreased from 4.0 cm for corn silking at 682 GDD to 2.5 cm for corn silking at 960 GDD, and then increased sharply to 5.5 cm for corn silking at 1050 GDD and remained high until late in the season. Damage to seed corn increased from 10 cm2/ear for corn silking early to a peak of 60 cm2/ear for corn silking at 1005 GDD, then gradually declined to ca. 35 cm2/ear for late silking corn. This represented a loss of 40–250 kg/10,000 ears. The regression of damage to population was calculated for both processing and seed corn.