Evaluation of Fungicides for Controlling Alternaria Leaf Spot of Broccoli in Arizona, 2025

Alternaria leaf spot, caused by Alternaria brassicicola, is a major disease that affects all cultivated brassicas worldwide. The typical symptoms are characterized by expanding small black lesions into large lesions with a ‘target-spot’ pattern of concentric rings. Stem and petiole infections manifest as dark, elongated lesions, while head infection results in black spots and rot across curds, significantly reducing harvest quality. This report evaluates the efficacy and crop safety of fungicides in controlling Alternaria leaf spot. The field trial was conducted in 2025 on Brassica oleracea var. italica ‘Castle Dome’. The results from this trial will help broccoli growers in the southwestern US make informed decisions when developing spray programs.