Downy Mildew of Broccoli -Promising New Fungicides for Disease Control

Downy mildew of broccoli, caused by the fungus Peronospora parasitica, is a perennial disease problem affecting winter broccoli production in Arizona. During 1985-87, potential systemic fungicides were evaluated in the field for disease control. In the 1985-86 season, a period of high disease incidence, lesion development was significantly reduced by fosetyl-Al (44 %), phosphorous acid (42 %), oxadixyl + mancozeb (35 %), chlorothalonil (33 %), metalaxyl + mancozeb (30 %) and metalaxyl + chlorothalonil (28 %). During the 1986 -87 growing season, disease incidence was low and lesion development was significantly reduced by phosphorous acid (82 %), fosetyl -Al or oxadixyl + chlorothalonil (77 %), metalaxyl + chlorothalonil (68 %) and chlorothalonil (54 %). Fosetyl-Al, phosphorous acid and oxadixyl were as effective as currently available fungicides ( metalaxyl and chlorothalonil) for control of downy mildew of broccoli in Arizona.