Figure 40. Flow diagram of pest management decisions for European corn borer (ECB) and corn earworm (CEW) on fresh market sweet corn.

The criteria for treating fresh market sweet corn for European corn borer or fall armyworm control (Figure 40) before tasseling are 30 percent or more of the plants show leaf feeding in the whorl and have live larvae, or 20 or more unhatched egg masses are found per 100 plants. Usually one whorl application of insecticide is sufficient to prevent economic loss in the number of marketable ears. Foliar treatments of granules or high-volume sprays directed into the whorl by ground application equipment are the most effective. For early tassel infestations, treat if 15 percent or more of the plants have live larvae or fall armyworms feeding on the emerging tassels. Properly timed treatment is very important during this period. As the tassels emerge, larvae disperse to other plant parts and are more exposed to insecticide. Larvae present during tasseling also have a greater chance to invade the developing ear; therefore, surviving larvae can cause significant quality problems.

Depending on location, the criteria for treating fresh market sweet corn during silking (Figure 40) often may be based on the extent of corn earworm activity, especially in late-planted sweet corn. Cone-shaped wire mesh 75:50 pheromone traps baited with pheromone lures (Hercon¨) are very consistent in detecting corn earworm flights and usually are more reliable than blacklight traps. The 75:50 for the pheromone trap refers to the 75 centimeter diameter base of the outer cone and the 50 centimeter opening of the more shallow inner cone. For plantings that are silking when the earworm is absent, begin treatments at the first sign of silking, if European corn borer catches in blacklight traps reach 5 moths or more per night, or if egg laying and leaf feeding are evident on the presilk stages of younger plantings on the same farm. In younger plantings, levels of 10 or more egg masses per 100 plants or more than 15 percent of the plants showing fresh feeding indicate that European corn borer or fall armyworm moths (or both) are laying eggs in nearby sweet corn in the silk stage. Repeat treatments every 6 days if European corn borer blacklight trap catches are 5 to 10 per night, every 5 days if catches are 11 to 20 per night, and every 4 days if catches exceed 20, provided that corn earworm pheromone trap catches are less than 6 per night. For plantings that are silking when the corn earworm is active, begin treatments after initial silk, if corn earworm pheromone trap catches average 2 or more moths per night. Repeat sprays every 6 days if pheromone trap catches are 2 to 5 per night, every 5 days if catches are 6 to 10 per night, every 3 to 4 days if catches are 11 to 50 per night, or every 2 to 3 days if catches are greater than 50.

Maximum control during silking is achieved with high-volume sprays of insecticides using a high clearance boom applicator with solid cone nozzles dropped between rows and directed at the ear zone. Aerial application, either fixed-wing or helicopter, also provides adequate coverage if used at maximum spray volume; 4 gallons of water per acre is adequate when applied by helicopter.

Air-blast sprayers are not recommended for sweet corn because coverage is dependent on prevailing winds. Research in Minnesota indicated that only the first 3 to 4 rows of a 10-row spray received minimum droplet coverage, leaving the remaining rows inadequately treated. If this is the only option, the numbers of rows sprayed by air-blast application should be adjusted to the variety's canopy structure. Transfer extensions also can be added to certain applicators to direct the air blast down through the canopy, which improves the spray distribution across the rows. For ground application, high- volume sprays of 40 to 60 gallons per acre should be used whenever possible. High pressure also is desirable, particularly for penetrating the silks.

When treating with insecticides, be sure to observe the label restrictions for the minimum number of days before harvest. Note: application of insecticide during pollen shedding can seriously reduce bee populations. If an insecticide must be applied, select a material with low toxicity to bees. Also, apply during late afternoon or at night; research in Delaware has shown that bees usually forage corn for pollen mainly in the morning and seldom in the afternoon.