Corn earworm is one of the most challenging pests of sweet corn. The moths are carried on trade winds from over wintering locations in the southern states. Summer storm fronts often drop large numbers of moths across Southern Ontario. Once here, the female moths can lay up to 2,000 eggs over the course of a 14-day lifespan.
Control measures must be taken during the narrow window of opportunity between when the egg hatches and when the larvae enter the protection of the husk. To further complicate matters, this pest has developed resistance to the pyrethroid family of insecticides. Depending on the year, the level of resistance can vary from 40-60% of the corn earworm population.
Research in the mid-western US suggests that the timing of the spray application is essential for good control. Apply a protective insecticide at first silk, followed by a second application 3-4 days later. Coragen Insecticide is an effective alternative to the pyrethroid insecticides.
For more information on the Corn Earworm and Integrated Pest Management of Sweet Corn visit Ontario Crop IPM at: http://www.omafra.gov.on.ca/IPM/english/index.html
 Hutchison et al. 2007. Evidence for Decreasing Helicoverpa zea Susceptibility to Pyrethroid Insecticides in the Mid-Western United States. Plant Management Network, 19th July, 2007.