Cabbage Black Rot
Dan Egel, Extension Vegetable Pathologist, Purdue University
Last week, I observed a large field of cabbage just beginning to form heads. While the crop initially appeared healthy, close inspection revealed the disease black rot on the lower leaves. All vegetables in the crucifer family, including broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, mustard, radish, rutabaga, and turnip, are susceptible to this bacterial disease known as black rot.
Lesions of black rot may start out as chlorotic (yellow) areas before growing into necrotic (brown) V-shaped lesions with chlorotic margins (See Figures 1 and 2). In severe cases, the infected areas may extend to the base of the leaf and the entire plant may be stunted.
Fortunately for this cabbage grower, only the lower leaves were affected; the crop will probably be able to mature with minimal damage from black rot. Homeowners should also check for the presence of this disease in the vegetable garden.
To control black rot of cabbage, purchase only disease free transplants or seed that has been tested for the bacterial pathogen. Commercial growers should use fields that have been rotated out of plants in the cabbage family for 2 years or more. A copper containing fungicide will slow the spread of black rot of cabbage to uninfected plants.
More info: Black rot of crucifers - The Ohio State University
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Figure 1: Early symptoms of black rot of cabbage may include chlorotic (yellow) areas along the margin of leaves.
Figure 2: Typical symptoms of black rot include V-shaped necrotic (brown) areas at the margin of leaves. Necrotic areas are often surrounded by yellow (chlorotic) areas.