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Distribution, Reproduction, and Movement of Phytophthora cinnamomi on Sites Highly Conducive to Jarrah Dieback in South Western Australia. S. R. Shea, Western Australian Forests Department, Dwellingup. B. L. Shearer, J. T. Tippett, and P. M. Deegan, Western Australian Forests Department, Dwellingup. Plant Dis. 67:970-973. Accepted for publication 6 March 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-970.

Phytophthora cinnamomi, which causes death of Eucalyptus marginata and other species in the jarrah forest of south Western Australia, was recovered at a high inoculum density as deep as 75 cm in soil immediately above a concreted lateritic layer. It was shown that the fungus can produce zoospores in soil at the interface of the lateritic layer and that zoospores are transmitted laterally in water flowing at the surface of the layer on sites of decline. It is proposed that the rapid mass decline and death of jarrah that has been observed is a consequence of these specific site characteristics, which allow infection and destruction of the vertical root system of jarrah by P. cinnamomi.