P-700 - Fungicide Resistance to Propiconazole in Exserohilum turcicum Population from Maize in Florida

Northern Corn Leaf Blight (NCLB), caused by Exserohilum turcicum, is the most significant maize disease in Florida. Although chemical control remains a primary management strategy, persistent challenges in disease control indicate complex pathogen dynamics. Previous research has confirmed the presence of resistant E. turcicum isolates to Propiconazole in Florida and established a discriminatory dose of 1 µg/ml for resistance screening. This study assessed the fungicide sensitivity of 300 E. turcicum isolates collected from sweet corn, field corn, and sorghum grown in six Florida counties: Palm Beach, Miami-Dade, Martin, Hendry, Suwannee, and Marion. In vitro assays were conducted to evaluate fungal growth on media amended with the discriminatory dose of Propiconazole, compared to non-amended controls. Relative growth was calculated as the percentage of mycelial growth on fungicide-amended media compared to the control. Isolates were classified as resistant if they exhibited ≥50% relative growth at the discriminatory dose. This study aims to determine the prevalence and distribution of Propiconazole resistance in E. turcicum populations across Florida cropping systems. The findings will provide insight into the extent of resistance development, help explain inconsistent fungicide performance in the field, and inform more sustainable and effective disease management strategies for NCLB.