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 metalaxyl 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 effective. Application of metalaxyl as a soil drench suppressed canker development when the treated trees were subsequently inoculated with Phytophthora cactorum. Fosetyl-Al significantly reduced the growth of fungus compared with cymoxanil, dimethomorph and control but it was not as effective as metalaxyl. Again, dimethomorph and cymoxanil did not influence 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 I-lad been drenched with the tested chemicals 20 days before, and inoculated on the cambium side with P. cactorum. Metalaxyl was the most effective fungicide and fosetyl-Al significantly reduced the development of fungus compared with dimethomorph, cymoxanil and the untreated strips. Colonization of strips treated with dimethomorph was significantly less than untreated strips. In contrast, cymoxanil did not inhibit the growth of fungus. Application of metalaxyl or fosetyl-Al as trunk paint ol a soil drench appear to be effective procedures for preventing Phytophthora rot of peach trees.