Figure 4. Blacklight trap equipped with a 15-watt bulb (M. E. Rice)

Efficient and accurate procedures for detecting treatable populations of European corn borer in cotton are continually being developed. Research has shown that egg masses cannot be found readily because of relatively low egg mass to leaf area ratio, generally wide egg mass distribution, and high labor requirement to locate them. Scouting should focus on detecting early instars on the lower portion of cotton bolls between the boll wall and bract, particularly on bolls in the lower half of the cotton plant. Random samples of 100 or more large, lower canopy bolls should be examined for larvae in each field. This procedure gives a reliable estimate of infestation levels; however, larvae often are inside tunnels or are otherwise inaccessible to insecticides when discovered. If larvae have not tunneled, use a treatment threshold of 3 per-cent of plants with live larvae.

Moth abundance estimates can be made with blacklight traps (Figure 4) or pheromone traps. Flight initiation and duration are important to the timing of scouting and other management decisions. The most favorable placement of pheromone traps is within the field, with the base of the trap below the top of the canopy. Performance of in-field traps is affected minimally by insecticide sprays.

Detection efforts should be focused on fields that are attractive to European corn borer moths. Late maturing, rank growth, and succulent cotton fields are the most attractive. Cotton fields that are relatively close to alternate cultivated hosts (e.g., corn fields) as well as cotton fields infested with weed hosts (e.g., cocklebur) also may be more prone to infestation.