Die-back in the mixed hardwood forests of eastern Victoria: A preliminary report

Abstract

The distribution and symptoms of die-back in the mixed-species eucalypt hardwood forests of eastern Victoria are described. The disease was recognizedin 1952 in small patches of forest situated in the flat, badly drained sandy coastal soils and has spread rapidly. This spread was associated with above-average rainfall during spring, summer, and autumn. Disease symptoms were similar to that caused by drought, and were observed best during dry periods following summer rain. The lupin bait of Chee and Newhook was used to isolate Phytophthora cinna- momi from the diseased areas, and the field symptoms seen on susceptible eucalypts of the subgenus Renantherae were similar to those observed on young saplings inoculated with P. cinnamomi in the greenhouse. Species of the subgenus Macrantherae observed in the forests and tested in the greenhouse are tolerant to the disease. Estimates of population density indices of the fungus gave highest values in areas where the disease was most active. The fungus was not isolated from adjacent healthy forests. Improvements in the baiting and identification of P. cinnamomi with use of excised lupin radicles floated over a small sample of soil in a petri dish are described. Several variants of the fungus with differing growth rates were isolated.