Effects of simulated chronic defoliation in summer on growth and survival of blue gum (Eucalyptus globulusLabill) within young plantations in northern Victoria

Summary The combined effects of two consecutive simulated partial and total defoliations of upper, lower and total crowns of 1.7-year- old plantings of Eucalyptus globulus during summer on height, stem basal area and volume increment are described. One hundred per cent crown defoliation suppressed height increment relative to the control treatment soon after the second defoliation, whereas the 100% lower crown defoliation boosted height growth throughout the post-defoliation period. Stem basal area increments were significantly reduced only by the 100% total crown defoliation, which also suppressed stem volume increment relative to the other treatments. None of the treatments affected tree survival. The implications of the results for eucalypt plantation managers are that populations of insect pests likely to cause total crown defoliation during summer in young E. globulus stands prior to canopy closure should be controlled at the earliest opportunity with an effective and appropriately registered insecticide. No action is required when moderate to severe defoliation is expected in either the upper or lower crowns. Moreover, pruning of lower crown branches during summer could boost height growth and accelerate canopy closure, a condition which suppresses infestations by light-seeking leaf-consuming leafblister sawflies, leaf beetles and Christmas beetles.