Use of metham sodium to eliminate Phytophthora spp. from roading gravel
Lateritic gravel is used for road building in Western Australia, with about 8 million m3 required annually. The introduced, soil-borne pathogen Phytophthora cinnamomi, which is associated with mortality of native plants, has been widely spread by using gravel from infested pits. Uninfested gravel is in demand, and in short supply. The biocide metham sodium is registered by the Australian Pesticides and Veterinary Medicine Authority (APVMA) as a soil fumigant, but the registered application method is unsuitable for treating gravel. In moist soil metham sodium decomposes into the fumigant-like pesticide, methyl isothiocyanate (MITC). Field experiments in which metham sodium was applied during the construction of 4 m3 gravel stockpiles, showed Phytophthora spp. are killed within 2 weeks of treatment with 80 mL m3–1 metham sodium. MITC is sealed within the stockpile by surface crusting; it was only detected 5 m downwind within the first 24 h of treatment. It was not detected in gravel 28 days after treatment. This application method that can safely eliminate Phytophthora spp. from infested gravel has been registered by the APVMA, allowing scaling-up trials to be considered.
KeywordsChemical control Dieback Gravel pits Plant disease
We thank Main Roads Western Australia, Nufarm Australia Limited, B&J Catalano Pty Ltd. and the Minerals and Energy Research Institute of Western Australia for financial support; Nufarm Australia Limited and B&J Catalano Pty Ltd. also provided in kind support. We thank the Department of Agriculture and Food Western Australia for allowing us to conduct the field trials at their Medina Research Station under the Australian Pesticides and Veterinary Medicines Authority Permit Number PER 7250, and Research Station staff for assistance with the field trials and the loan of personal protective equipment. The Department of Conservation and Environment is thanked for the gift of inoculated pine plugs, additional pine plugs, and cultures of Phytophthora cinnamomi. They are also thanks for discussions of how this process could be used operationally. L. Kupsky is thanked for preparing agar and L. E. McGurk assisted with preparing the field inoculum. Two anonymous referees are thanked for their constructive criticisms which have improved the manuscript.
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