Response of Cotton to Damage by Insect Pests in Australia: Pest Management Trials

Twenty pest management experiments were done between 1985 and 1988 at 11 sites in the Namoi valley of NSW, Australia, on four varieties of cotton, Gossypium hirsutum L. In every experiment, the control treatment, consisting of the standard action thresholds for the common insect pests of the region, was compared with higher earlyseason thresholds. Lower thresholds were tested at one site for three seasons and at three other sites for the last season. The Australian-bred okra leaf variety Siokra consistently outyielded normal leaf variety DP90 and required fewer sprays. ‘Siokra’, with higher early season pest thresholds, had yields similar to or better than the control treatment. DP90 compensated less for early-season damage and was therefore more susceptible to earlyseason damage than ‘Siokra’, often resulting in a lower yield for the treatments with higher thresholds. There was no threshold treatment that was always the best, but there was a trend for treatments with higher early-season thresholds to be more profitable than the control with the Australian varieties ‘Siokra’ and ‘Sicala’, but not with ‘DP90’, Higher thresholds early in the season, and the resultant less stringent pest control, did not consistently delay the crop or lead to more late-season applications of costly insecticides. The less exhaustively tested treatment with low thresholds always yielded well. It was the most profitable only 1 yr in 3 with Siokra but 2 yr in 3 with ‘DP90’.