Developing a profitable and sustainable fungicide program to control northern and southern corn leaf blights on sweet corn in Florida

Northern (<i>Exserohilum turcicum</i>) and southern (<i>Bipolaris maydis</i>) corn leaf blights threaten fresh-market sweet corn in Florida, yet region-specific data on efficacy and economics of fungicide programs are scarce. Four replicated field trials were conducted in Belle Glade, FL (spring 2023, spring 2024, fall 2024, spring 2025) comparing eight treatments with foliar programs that contrasted early pre-tassel (V3/V7 growth stages; mancozeb mixed with single-site fungicides) with systemic-only programs beginning at tasseling/silking (VT/R1). Yield was collected in 2023 and 2025. Under high disease pressure (disease severity > 80%), early fungicide programs reduced relative area under disease progress curve (rAUDPC) more than VT and R1 programs. Results were consistent across independent epidemics: in southern corn leaf blight epidemics, programs initiated at V3 and V7 limited mean rAUDPC to 19% versus 47% in non-treated; in northern corn leaf blight epidemic, V3/V7 programs averaged 6% versus 36% in non-treated. Yield responses paralleled disease control. The best programs protected yield by 2.44 t ha⁻¹ in 2023 (two pass V7 and R1) and by 1.93 t ha⁻¹ in 2025 (four pass grower standard). Treated plots showed greater kernel filling, which mediated most of yield response. Economic results were favorable, with typical program costs covered by ≤0.4 t ha⁻¹ of protected yield, and top programs demonstrated ROI of 92 to 762%. In subtropical sweet corn, starting protection by V7 and maintaining coverage through VT/R1 maximizes blight suppression, safeguards kernel fill, and improves profitability. Streamlined two-pass programs can match three- or four-pass schedules while reducing inputs and stewardship risks.