The combined effects of two consecutive simulated partial and total defoliations of upper, lower and total crowns of I. 7 -yearold 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 I 00% 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.
1 The sirex woodwasp, Sirex noctilio has been a significant pest of radiata pine plantations in Victoria since 1961. Outbreaks are usually associated with susceptible trees being under some form of stress including the effects of drought and overcrowding. 2 This paper reviews the spread of sirex and the history and efficacy of biological control programmes implemented against sirex in Victoria from 1970 to 2006. 3 Of the numerous biological control agents released, the most effective in managing sirex have been the nematode Beddingia siricidicola and the parasitic wasp Ibalia leucospoides. Several other parasitic wasps such as Schlettererius cinctipes and Megarhyssa nortoni nortoni have also established but provide only minimal control. 4 While rates of I. leucospoides parasitism have improved over time, it is unlikely that this improvement will continue substantially past current levels. 5 In recent years, issues have arisen regarding a decline in the infectivity of B. siricidicola necessitating a re-evaluation of strategies and development of techniques to overcome this problem. 6 Ongoing research using Random Amplification of Polymorphic DNA (RAPD) testing is underway to accurately determine nematode strains and associated infectivity present in plantations in the field in order to develop management strategies to re-introduce more effective strains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.