Optimizing management of cercospora leaf spot (Cercospora beticola) of sugarbeet in the wake of fungicide resistance

AbstractCercospora leaf spot (CLS), caused by Cercospora beticola, is the most detrimental disease of sugar beet in temperate climates. In the Great Lakes region, CLS was well managed by pyraclostrobin-based programmes using the decision support tool BEETcast™. Due to C. beticola resistance to pyraclostrobin in the region, other groups of fungicides were evaluated. Field experiments were conducted at six sites from 2013 to 2015 in Pain Court (PC) and Ridgetown (RT), Ontario. BEETcast™ application schedules for prothioconazole and mancozeb as well as carrier volume (115 and 235 L ha−1) were compared with label-based (calendar) applications. When disease intensity was high, the conservative calendar application schedule reduced the standardized area under the disease progress curve (sAUDPC) by an average of 84% compared with all BEETcast™ schedules, and the BEETcast™ 50/35 schedule (235 L ha−1) reduced sAUDPC by 48% compared with the 55/50 schedules. However, there were fewer differences among application s...