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

Abstract

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.