Abstract
Summary The distribution and severity of pine needle blight disease (PNB), caused in spring 1989 by an outbreak of the needle cast pathogen Dothistroma septospora, was assessed within a 10 km radius of two study sites near Myrtleford in the Wangaratta Pinus radiata plantation complex of north-eastern Victoria. Areas of severe needle cast were located on colour aerial photographs in spring 1989, then checked by ground survey for the percentage of visible crowns infected. Population levels of the Sirex wasp (Sirex noctilio), rated in terms of the cumulative percentage tree mortality induced by the wasp since 1989, were estimated in autumn/winter 1991. Twenty-one unthinned plots, each of 400 trees aged 14–15 years, were examined for S. noctilio and associated symptoms of D. septospora. The effectiveness of parasitoids was evaluated in the laboratory by monitoring total insect emergents from 222 billets (0.8 m long), cut in winter 1991 from 100 herbicide-injected ‘Sirex’ trap trees. All emergents of S. noctil...
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