Activity of metalaxyl-M+mancozeb, fosetyl-Al, and phosphorous acid against Phytophthora crown and root rot of apricot and cherry caused by Phytophthora palmivora

Crown and root rot, caused by the Oomycete pathogen Phytophthora palmivora, has become a destructive disease of apricot and cherry in eastern Turkey. There are no currently registered fungicides labeled for its control. In greenhouse experiments conducted in 2012 and 2013, 1-year-old potted apricot rootstock Zerdali and cherry rootstock Mahaleb plants were treated either with foliar spray of fosetyl-Al (140, 160, and 180 g a.i./100 l) or phosphorous acid (187.5, 200, and 215 g a.i./100 l) or soil drench of 100 ml of metalaxyl-M (= mefenoxam)+mancozeb (12+192, 16+256, and 20+320 g a.i./100 l) one day after wound inoculation of crowns and roots. In both years, phosphorous acid at 200 and 215 g a.i./100 l, fosetyl-Al at 160 and 180 g a.i./100 l, and metalaxyl-M+mancozeb at 20+320 g a.i./100 l significantly reduced the root rot severity on Zerdali by 70.68-80.00% and crown rot severity on both Zerdali and Mahaleb, by 68.32-91.96 and 74.21-82.60%, respectively, compared with phosphorous acid at 187.5 g a.i./100 l, fosetyl-Al at 140 g a.i./100 l, metalaxyl-M+mancozeb at 12+192 and 16+256 g a.i./100 l and control. Moreover, fosetyl-Al at 180 g a.i./100 l and metalaxyl-M+mancozeb at 20+320 g a.i./100 l significantly reduced the root rot severity on Mahaleb compared to fosetyl-Al at 140 and 160 g a.i./100 l, metalaxyl-M+mancozeb at 12+192 and 16+256 g a.i./100 l, phosphorous acid treatments and control in 2012, providing the best control of the disease by 88.00-90.68%. Two/three phosphorous acid foliar applications at 200 g a.i./100 l suppressed symptom development when field applications were made on a curative basis in 2014 and 2015.