Recent Invasions of Australia and New Zealand by Pathogenic Fungi and Counter Measures1

Abstract

Despite the relative isolation of Australia and New Zealand and the strict quarantine regulations long imposed, many plant diseases have been introduced in recent years. The article analyzes 26 cases since 1960 which seem certain to be new arrivals, and have some economic significance. Wind‐borne introduction from the islands to the north seems likely in several cases (Cochliobolus heterostrophus, Peronosclerospora maydis, Puccinia arachidis, Mycosphaerella fijiensis var. difformis) and air currents are certainly responsible for many arrivals in New Zealand from Australia (acacia rusts, Puccinia menthae, P. helianthi. Puccinia melanocephal (sugar cane rust) is one case of possible intercontinental movement west to east on prevailing air currents (from Africa to India and the Far East, then Australia and Central America). However, accidental introduction by air travellers, or illegally introduced planting material, seems most likely to explain the recent appearance in Australia of Puccinia striiformis and Melampsora spp. on poplar, even if these have since spread naturally to New Zealand. Dothistroma septospora, causing a needle blight of Pinus radiata, is unusual in that it apparently moved from New Zealand to Australia (around 1975). Internal restrictions can limit further spread in some cases. Otherwise, the « cost » of these introductions has mainly arisen from the need for fungicide treatments and from the abondonment of valuable, but susceptible, cultivars. Introduced fungi may not behave as expected on the basis of earlier biological studies. Thus, P. striiformis survives the harsh Australian summers while D. septospora which necessitates costly fungicide treatments in New Zealand, has remained isolated and unimportant in Australia.