EFFECTS OF DEFOLIATION ON DRYLAND WHEAT PRODUCTION IN CENTRAL QUEENSLAND

The effect of insect defoliation on grain yield, nitrogen (N) content, and gross value of dryland wheat was simulated by removing blades from the flag leaf, top 2 leaves (flag leaf plus the one below it), and all leaves, 100 days after planting the crop. When blades were removed from the top 2 leaves and all leaves, respectively, significant (P<0.05) reductions of 13.5 and 17.3% in grain yield, 9.2 and 11.9% in head weight, and 7.6 and 13.2% in 1000-grain weight were recorded. Defoliation did not significantly decrease grain number/m2. When blades were removed from the flag leaf, top 2 leaves, and all leaves, respectively, significant (P<0.05) reductions of 9.5, 17.3, and 14.0% in grain N concentration, and 14.2, 28.4, and 28.8% in grain N yield (g/m2), occurred. Gross values of the yields from different treatments were ranked (differences at P = 0.05) control > flag leaf blade removed > top 2 leaves removed = all leaves removed.