Timing and frequency of fungicide applications for the management of sugarcane brown rust

The frequency and application timing of fluxapyroxad + pyraclostrobin fungicides for management of sugarcane brown rust, caused by Puccinia melanocephala, was evaluated during two growing seasons (2016 and 2017) in Belle Glade, FL. Although the rust epidemic duration was longer in 2017 than in 2016, three applications of fluxapyroxad + pyraclostrobin during early, mid, and late epidemic season at three week-intervals resulted in 40-42% decrease of disease severity on the top visible dewlap leaf (expressed as the area under disease progress curve). These fungicide applications were also associated with a 27-35% increase in mean stalk weight as compared to untreated control plants. Two fungicide applications during early and mid-epidemic season resulted in similar stalk weight gain (25-32%) and 30-39% reduction of disease severity as compared to untreated control. Single applications either during early or mid-epidemic season were the least effective in reducing rust severity and increasing mean stalk weight. Therefore, at least two applications of fluxapyroxad + pyraclostrobin initiated during early epidemic season are necessary for best management of sugarcane brown rust in Florida. Based on increase of estimated commercial yields, the most beneficial chemical control was achieved with two rather than three fungicide sprays at three to four weeks intervals.