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Evaluation of Three Treatments for Eradication of Phytophthora cinnamomi from Deep, Leached Sands in Southwest Australia. TOMC J. HILL, Research Centre, Department of Conservation and Land Management, Hayman Rd., Como, Western Australia, 6152. JOANNA T. TIPPETT, and BRYAN L. SHEARER, Research Centre, Department of Conservation and Land Management, Hayman Rd., Como, Western Australia, 6152. Plant Dis. 79:122-127. Accepted for publication 13 October 1994. Copyright 1995 The American Phytopathological Society 122 Plant. DOI: 10.1094/PD-79-0122.

Three treatments were evaluated against localized infections caused by Phytophthora cinnamomi in tracts of species-rich Banksia woodlands and scrub-heaths in deep, leached sands in south-west Australia. The treatments were (I) application of herbicide to kill all vegetation, (2) herbicide plus 5 or 15 g (a.i.) m-2 metalaxyl, and (3) herbicide plus fumigation with 27 or 54 L m-2 of 1% formaldehyde. The effectiveness of the treatments was assessed in 225-m2 plots in two Jandakot sand sites using buried pine branch plugs inoculated with P. cinnamomi at 0.3 m and 1.3 m depth, and from naturally infected soil cores taken lo 0.4 m depth. After 20 mo, P. cinnamomi was recovered from 77 and 87% of plugs buried at 0.3 and 1.3 m depth, respectively, in the herbicide plots, and from 4.6% of soil samples (21% in controls). With metalaxyl treatment, plug recovery was nil at 0.3 m and 3% at 1.3 m after 9 mo, and in soil samples taken after 10 and 20 mo, recovery was also nil. Formaldehyde efficacy varied with site; on one site, plug recovery was 4 and 2% at 0.3 and 1.3 m, respectively. From isolations from collar tissue of Banksia attenuata and adjacent soil samples, the fungus was retrieved from 100% of dying trees, 96% of recently dead trees and 56% of trees dead for more than 1 or 2 yr. In recently dead trees, fungal recovery from tap roots at 1.0 and 2.0 m depth was 87 and 48%, respectively. The longevity and occurrence of P. cinnamomi at deep depths precludes any attempt at rapid chemical eradication, although metalaxyl could be used to contain highly contagious sites. Confinement or eradication of the pathogen may be achieved by keeping sites completely bare for many years.