Corn is a favorite of many pests. Prevention is usually the best defense. Plant disease-resistant varieties, encourage beneficial insects, and rotate where you plant corn each year. If cut worms were a problem in past years, drench the soil with parasitic nematodes a couple of weeks before planting. 

Use floating row-cover to help prevent damage from birds, corn borers, or slugs. Check leaves for small holes regularly. If you find holes, spray with Bt each week as long as new holes appear. If worms have been an issue, place a few drops of mineral oil into the tip of each ear after the silk turns brown.