How to Manage Pests
UC Pest Management Guidelines
The two Alternaria species, A. brassicae and A. brassicicola, cause similar symptoms;small, dark specks first develop on leaves and later enlarge into circular, tan spots (0.25-0.5 inch in diameter). The spots caused by A. brassicicola tend to be darker than those caused by A. brassicae. If conditions are favorable, dark green spores of the pathogen will grow on the spots. Such growth causes the spots to have concentric rings in them. Old leafspots become papery in texture and may tear. When the dry tissue falls out, a shothole effect results.
Alternaria leafspot is usually not an economic concern on cole crops. It occasionally is a problem on cabbage during cool, rainy months. The pathogen can also infect Brussels sprouts, broccoli, and cauliflower. Leafy crucifers that are harvested for their leaves (red mustard, Chinese cabbage, tat tsoi, and Mizuna mustard) are also susceptible to Alternaria brassicae and can be seriously damaged by this pathogen. Disease is favored by moist conditions. Spores are spread by winds and splashing water. The fungus does not survive in soil, but is carried over in crucifer seed, on weed or volunteer hosts, or on undecomposed crop residue.
Use clean seed and practice crop rotation. Fungicides applied as foliar sprays will control this disease.
UC IPM Pest Management Guidelines: Cole Crops