In the desert southwest, pink bollworm (PBW) moths emerge from late March through mid June. After mating, females oviposit on cotton stems, leaves, terminals and squares. If the presence of hostable squares were delayed to the point that moth emergence were complete, or nearly so, initial infestation levels could be substantially reduced. Ethephon (Prep) is known to cause abscission of squares, flowers, and young bolls of cotton. This is a preliminary and brief report of 1988 trials conducted in California's Palo Verde Valley, wherein Prep was applied to cotton at several rates and different stages of crop development.

Four DP-90 cotton fields ranging from 28 to 38 A and planted between 3/20 and 3/25/88 were selected. Rates of Prep employed were 0.25, 0.75, and 1.15# a.i./A. Times of application varied from initiation of squaring to early flowering. Each treatment regime was utilized for two, 6-row plots per field. Two 6-row plots were left as untreated controls in each field. Dates of harvest for the four fields ranged from 9/17-9/28/88 (average of 9/24 for first pick) and 10/13-10/18/88 (average of 10/17 for second pick.

Treatment of cotton plants at initiation of squaring, even with the high rate of Prep (1.15# a.i./A), did not appreciably delay time or extent of total flowers and infested flowers. Yield was, however, decreased by 5%. The medium rate of Prep (0.75# a.i./A) applied soon after hostable squares (one-third grown) were present delayed flowering. Yields were reduced by 31%. An additional delay in application until soon after flowers were present, magnified these effects (yield reduction of 58%). Applications of Prep at 0.75 and 1.15# a.i./A at the same time in cotton's development (about midway between hostable squares and flowers) also delayed flowering and decreased yields with the highest rate causing the greatest loss of fruiting forms and yield (yield reduction of 11 and 33% respectively).

It was expected that the medium and high rates of Prep, applied when abundant hostable squares were present, would delay the onset of flowering and the time that infested flowers were detected. It was hoped that Prep would also reduce the extent of PBW infested flowers as a result of earlier hostable square removal. Although the latter was generally the case, the marked delay in flowering and the resultant decrease in yield for most of the plots force the conclusion that, in 1988, any advantage in PBW control was more than offset by a reduction in harvestable seed cotton.