Foliar pests and pathogens of Eucalyptus dunnii plantations in southern Queensland

Abstract

Summary Eucalyptus dunnii is grown in plantations in subtropical Queensland, beyond its endemic distribution of northern NSW. As the plantation industry has expanded into subtropical Australia there has been an increase in the incidence of defoliating insects and foliar pathogens. This study measured the incidence and severity of damage (abiotic damage, fungal damage, insect defoliation, insect-induced necrosis and or other insect damage), four times over one year, in eight plantations aged 1,2,3 and 4 y where E. dunnii was the dominant species: four near Brisbane and four near Bundaberg. Multidimensional scaling (MDS) analysis showed little separation between the two regions so all data for the study were combined. During the study period, the monthly rainfall was substantially lower than over the previous 30 y, particularly in all months except September to January where higher-than-average rainfall occurred in both regions. This resulted in a strong seasonal effect. The greatest damage was caused by defoliating insects (39.6% of total damage) most notably chrysomelids, followed by insect necrosis (19.2%). The pests and diseases causing most damage (e.g. chrysomelids) were present most of the year and are known to be multivoltine in subtropical regions of Australia. Only chrysomelid damage increased over the survey period, while fungal damage decreased slightly in the same period. Insect necrosis was present all year round, with most damage occurring in winter and least damage in summer. Other insect damage was highest in 1,75–3-y-old trees, peaking in winter at 9.1% in the 1.75-y-old trees. This study has provided some interesting insights into the incidence and severity of abiotic stress, pests and pathogens over four seasons. These findings may influence future plantation management of pests and diseases in establishing plantations.