IMPART OF MISTLETOES (AMYEMA-MIQUELII) ON HOST (EUCALYPTUS-BLAKELYI AND EUCALYPTUS-MELLIODORA) SURVIVAL AND GROWTH IN TEMPERATE AUSTRALIA

The damaging effects of mistletoes Amyema spp. on host eucalypts in ru ral Australia concern many landholders, but few data are available to evaluate mistletoe impacts or formulate management strategies. We used an experimental disinfection approach to determine the effects of a p utative pest mistletoe, Amyema miquelii, on its two principal hosts, B lakely's red gum (Eucalyptus blakelyi) and yellow box (Eucalyptus mell iodora), on pastoral properties in northern New South Wales. For each host species, pairs of nearby trees were matched for height, diameter at breast height, level of mistletoe infestation and distance to neigh bouring trees. One tree per pair was chosen at random and all the mist letoes pruned. After 33 months all treated trees were still alive, but among control trees seven of 29 red gums and one of 20 yellow box tre es had died. The difference in survival between treated and control tr ees was significant for red gum. Among surviving pairs of trees, treat ed trees of both species had significantly greater diameter increments and significantly more foliage than untreated trees. After 33 months, the average increase in relative host foliage biomass attributable to removal of mistletoes was 22% in red gum and 24% in yellow box, compa red with untreated controls. The average increase in radial growth att ributable to mistletoe removal was 55% in red gum and 49% in yellow bo x. Diameter increment was negatively and linearly related to mistletoe infestation level in control trees of both species. The differences b etween infected and disinfected trees in this experiment may underesti mate the impact of Amyema miquelii on host growth because small amount s of host biomass were unavoidably lost during disinfection. In a sepa rate experiment, loss of host biomass had a significant negative impac t on diameter increment. Although the results indicate that control of serious Amyema miquelii infestation of individual trees will be worth while in terms of immediate host survival and higher growth rate, prud ent long-term management may well allow for the loss of small numbers of farm trees to mistletoes when planning tree recruitment and utilisa tion.