Effectiveness of metalaxyl, fosetyl-Al, dimethomorph, and cymoxanil against Phytophthora cactorum and P. citrophthora of peach tree

Metalaxyl, fosetyl-Al, dimethomorph and cymoxanil were applied as a soil drench to evaluate their ability to control in vitro and in vivo Phytophthora cactorum and P. citrophthora, agents of crown rot of peach tree. In the in vivo assays, metalaxyl, applied as soil drench at 2 g/tree, was the most effective, reducing growth of P. cactorum and P. citrophthora. Fosetyl-Al was less effective against both pathogens, while cymoxanil and dimethomorph did not inhibit growth. When scraped stem cankers were painted with metalaxyl, fosetyl-Al or dimethomorpth at 150 g/l Phytophthora colonization was inhibited, but cymoxanil applied in the same way was ineffective. In the in vitro tests, metalaxyl and dimethomorph at concentrations as low as 100 mg l-1 completely inhibited growth of P. cactorum and P. citrophthora. Fosetyl-Al only did so at concentration of 1500 mg l-1 and over. Cymoxanil was less effective since even at 2000 mg l-1 it did not prevent mycelial growth of P. cactorum and P. citrophthora. This study demonstrated that Phytophthora diseases of peach tree can be controlled by metalaxyl applied as a soil drench and by metalaxyl, fosetyl-Al and dimethomorph painted on scraped stem cankers.