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Donald M. Ferrin, Hadziabdic, Denita, Hollier, Clayton A., Overstreet, Charles
Alternaria leaf spot (black spot)caused by the fungus Alternaria brassicae is characterized by brown to black spots with concentric rings on the lower leaves. As the disease progresses, infected leaves turn yellow and drop.
Downy mildew is caused by fungus Peronospora parasitica. The pathogen can attack both seedlings and mature plants. Symptoms include vascular discoloration and can also predispose the plant to bacterial soft rot.
Downy mildew on the upper surface of the leaf. Symptoms initially appear as small yellow spots that eventually turn brown. On the underside of the leaf, white downy mold develops, which differs from powdery mildew symptoms.
Even though Alternaria leaf spot most commonly occurs on leaves, edible cauliflower curds can be affected also. These spots contain numerous spores that can be disseminated by wind, splashing water, people and equipment. Disease is favored by warm, moist conditions, in contrast to downy mildew.
The LSU AgCenter and the LSU College of Agriculture
