Eggs of Heliothis virescens (F.) were placed on cotton terminals at different times to determine the effects that the resulting larval damage would have on first harvest and total yield. Each year of a two-year study, eggs were placed on terminals on three dates or combinations of the three dates. In 1982 the dates were July 14, August 5, and August 18, and in 1983 the dates were June 30, July 15, and August 18. Within a year, all combinations of 0, 1, 2, and 3 infestations were evaluated. The eight treatments consisted of one treatment with no infestation, three with a single infestation, three with two infestations, and one with all three infestations. The treatments were applied to four cultivars, 'Stoneville 825', 'Stoneville 506', 'Deltapine 90' and LaHg 1488. The infestation rate was 5-6 eggs/terminal for 16 terminals in a 5.5 m row. The experimental design was a split-plot with infestation rates used as whole plots. There were eight replications each year.

The average first harvest lint yields were 449, 392, 461, and 445 kg/ha for the check (no infestation), first, second, and third dates of infestation, respectively. The average total yield for the check, first, second, and third dates of infestation was 644, 589, 648, and 634 kg/ha, respectively. The only consistent effect detected was the earliest infestation. Various combinations of infestations sometimes resulted in yield reduction equal to the first infestation alone, but none of the combinations were greater in yield reduction than the earliest infestation date. No infestation date X cultivar or infestation date X cultivar X year interactions were detected. This study indicates that one infestation date at about the pre-flowering to first flower stage is sufficient to result in significant reductions in first harvest and total yield.