EVALUATION OF 3 TREATMENTS FOR ERADICATION OF PHYTOPHTHORA-CINNAMOMI FROM DEEP, LEACHED SANDS IN SOUTHWEST AUSTRALIA

Three treatments were evaluated against localized infections caused by Phytophthora cinnamomi in tracts of species-rich Banksia woodlands an d scrub-heaths in deep, leached sands in southwest Australia. The trea tments were (1) application of herbicide to kill all vegetation, (2) h erbicide 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 effectivenes s of the treatments was assessed in 225-m(2) plots in two Jandakot san d 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 t o 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 herbicid e plots, and from 4.6% of soil samples (21% in controls). With metalax yl treatment, plug recovery was nil at 0.3 m and 3% at 1.3 m after 9 m o, and in soil samples taken after 10 and 20 mo, recovery was also nil . Formaldehyde efficacy varied with site; on one site, plug recovery w as 4 and 2% at 0.3 and 1.3 m, respectively. From isolations from colla r tissue of Banksia attenuata and adjacent soil samples, the fungus wa s retrieved from 100% of dying trees, 96% of recently dead trees and 5 6% of trees dead for more than 1 or 2 yr. In recently dead trees, fung al recovery from tap roots at 1.0 and 2.0 m depth was 87 and 48%, resp ectively. The longevity and occurrence of P. cinnamomi at deep depths precludes any attempt at rapid chemical eradication, although metalaxy l could be used to contain highly contagious sites. Confinement or era dication of the pathogen may be achieved by keeping sites completely b are for many years.