Effects of Metalaxyl, Fosetyl-Al, Dimethomorph and Cymoxanil on Phytophthora cactorum of Peach Tree

The activity of metalaxyl, fosetyl-Al, dimethomorph, and cymoxanil against Phytophthora crown rot of peach trees was examined. Application of fosetyl-Al or met- alaxyl by painting the trunk (150 g/l) of 3-year-old PR204 trees was inhibitory to growth of the fungus but neither dimethomorph nor cymoxanil were e€ective. Application of metalaxyl as a soil drench suppressed canker development when the treated trees were subse- quently inoculated with Phytophthora cactorum. Fose- tyl-Al signi®cantly reduced the growth of fungus compared with cymoxanil, dimethomorph and control but it was not as e€ective as metalaxyl. Again, dimethomorph and cymoxanil did not in¯uence canker development. Both metalaxyl and fosetyl-Al were active for at least 21 days after applications. Strips of trunk bark were removed from trees, that had been drenched with the tested chemicals 20 days before, and inoculated on the cambium side with P. cactorum. Metalaxyl was the most e€ective fungicide and fosetyl- Al signi®cantly reduced the development of fungus compared with dimethomorph, cymoxanil and the untreated strips. Colonization of strips treated with dimethomorph was signi®cantly less than untreated strips. In contrast, cymoxanil did not inhibit the growth of fungus. Application of metalaxyl or fosetyl- Al as trunk paint or a soil drench appear to be e€ective procedures for preventing Phytophthora rot of peach trees