RESPONSE OF COTTON, GOSSYPIUM-HIRSUTUM L, TO DAMAGE BY INSECT PESTS IN AUSTRALIA - MANUAL SIMULATION OF DAMAGE

Three experiments were done between 1984 and 1987 in manually simulated pest damage with up to 14 damage treatments in any year, involving different types and levels of damage at three stages of the season applied to three varieties, two plant populations, and two irrigation regimes. In these experiments, the cotton plant has again shown a considerable ability to compensate in terms of total lint yield for early damage, involving either the loss of the growing point or squares. Although severe damage or combinations of tip and square removal sometimes caused considerable delay in maturity, light and moderate damage had little effect. Damage treatments did not affect fiber attributes sufficiently to have incurred price penalties commercially, despite extreme delay in some cases. Damage treatments did not interact with plant populations and irrigation regimes but the locally bred okra leaf variety 'Siokra' was more responsive to damage than the normal leaf variety 'Deltapine 90', with increased yield at light to moderate levels of early damage and decreased yield at severe levels. Evidence was found in the data from these experiments for the occurrence of three out of four previously identified physiological mechanisms involved in compensation by the crop plant for damage: damage substituting for physiological shedding, increased boll weight and increased rate of flowering. There was no evidence of the fourth mechanism, increased boll set.