Alternaria Leaf Spot
Alternaria brassicae, A. brassicicola
Most crucifer plants are susceptible to Alternaria leaf spot and plants at all growth stages may be affected. Symptoms caused by the two pathogens are very similar and both may be found on the same plant. Infection of seedling stems may result in damping-off or stunted plants.
Leaf spots vary in size from pinpoints up to 5 cm in diameter. Typically lesions begin as small yellow areas that enlarge to about 1.5 cm in diameter and are dark colored spots with concentric rings. A brown discoloration of cauliflower and broccoli heads is caused by infections with these pathogens. The pathogen causes elliptical necrotic spots on seed stalks and seedpods. Pod lesions may extend into the pod interior and attack the seed causing them to shrivel.