Integration of Biorational and Conventional Fungicides with Host Resistance for the Management of Alternaria Leaf Blight and Head Rot in Broccoli

Alternaria blight and head rot (ABHR), primarily caused by Alternaria brassicicola, is a significant constraint in Virginia broccoli production, reducing yield and marketability. Although no ABHR resistant cultivars are available, less susceptible cultivars can slow disease development and reduce epidemic severity. Fungicides can limit disease, but efficacy varies with environment and pathogen pressure. To evaluate integrated strategies combining cultivar selection with fungicide use, field trials were conducted in 2023 and 2024. Broccoli cultivars ‘Burney’, ‘Emerald Crown’, and ‘Abrams’ were evaluated in split-plot trials with conventional and biorational fungicide programs. Additional trials assessed cultivar susceptibility without fungicides. Across years, ‘Burney’ consistently had lower foliar severity than ‘Emerald Crown’ and ‘Abrams’, although head rot responses were more variable. Conventional fungicide programs reduced foliar disease and, during low disease pressure, kept head rot-related yield loss within commercially acceptable levels. No single fungicide program was consistently superior across cultivars. Biorational programs did not reduce foliar symptoms, but polyoxin D alternated with copper hydroxide consistently reduced head rot in ‘Burney’. Cultivar × fungicide interactions for head rot were significant, emphasizing the importance of cultivar selection. In unsprayed trials, ‘Burney’, ‘Exp3622’, and ‘Abrams’ showed lower disease levels than other cultivars evaluated. Combining fungicides with partial cultivar resistance is essential for minimizing losses, and identifying ABHR-tolerant cultivars adapted to Eastern U.S. conditions will further strengthen integrated management strategies for broccoli production in the region.