European corn borer, Ostrinia nubilalis (Hubner), pheromone monitoring system and action thresholds for sweet corn

European corn borer, Ostrinia nubilalis (Hubner), is the primary pest sweet corn grown in Minnesota. Monitoring the initiation and duration of O. nubilalis flights is critical for pest management. Pheromone lure studies were conducted during 1992--1994 at Rosemount and Le Sueur, Minnesota, to determine the relative attractiveness of different ratios of (Z)- and (E)-11-tetradecenyl acetate isomers to O. nubilalis male moths. The timing of O. nubilalis flights based on pheromone and blacklight trap catches also were compared. The proportion of total moths captured indicated moths were highly attracted to lures with a ratio of isomers near 98:2 ( Z:E). A significant decline in attractiveness occurred in the 95:5 (Z:E) isomer range. Although first moth catch in pheromone traps usually coincided with blacklight traps, the estimated timing of 2 nd generation peak flight was significantly different between trap types. Experiments were conducted during 1995--1996 to determine the most efficient pheromone trap design. The conventional Hartstack trap, with a 75 cm base, was the most efficient pheromone trap for O. nubilalis males. Hartstack trap counts and the number of males captured in blacklight traps did not differ, however, the Hartstack trap detection of peak moth flight was delayed 4 to 15 days. Improved pheromone lures, available from Trece, Inc. and Hereon Environmental Co., were compared with our MN-lure and a blacklight trap during 1997. Both Trece and Hereon lures produced similar moth counts as the MN-lure. Although pheromone and blacklight traps did not differ in male moth counts, the pheromone trap again resulted in a delay of 4 to 8 d in detection of estimated peak flight. Action threshold studies were conducted during 1992--1996 to develop growth stage-specific action thresholds for three typical sweet corn hybrids. The probability of exceeding a 5% damaged ear threshold at harvest is quite high even at a 12.5% level of infestation. For early season hybrids, insecticide treatments should be applied at 5% infestation, regardless of plant growth stage. For mid- to late-season hybrids, treatments should be applied at 12.5% infestation level for vegetative growth stages, and 5% at tassel and silk growth stages.