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Black rot on cabbage caused by the seedborne bacterium Xanthomonas campestris pv. campestris. Note the large yellow-orange "V"-shaped lesions extending inward from the margin of the leaf. Veins in the infected area will turn black.
All crucifer crops are susceptible to black rot, including cabbage, broccoli, cauliflower, Brussels sprouts, Chinese cabbage, kale, radish, turnip, mustard, rutabaga, watercress, and arugula. Black rot is favored by warm, wet weather. These bacteria spread by means of water (surface water, irrigation water or splashing rain) and enter the plant through natural openings (stomates and hydathodes) or wounds.
Downy mildew is caused by the fungus-like pathogen (Oomycete), Peronospora parasitica. Initial symptoms consist of small yellow spots on the leaves that eventually turn brown as the disease progresses. Downy mildew is favored by cool, wet weather and may predispose plants to bacterial soft rot. Image courtesy of Clemson University.
Head rot of cabbage caused by the soilborne fungal pathogen Sclerotinia sclerotiorum is often referred to as "white mold." The most favorable conditions for disease development are cool, wet weather combined with high humidity and heavy dew.
Alternaria leaf spot caused by Alternaria spp. Elliptical necrotic lesions with a "bull's-eye" pattern are characteristic of this disease. Infected leaves eventually turn yellow and drop. Image courtesy of Clemson University - USDA Cooperative Extension.
The LSU AgCenter and the LSU College of Agriculture
