Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Cabbage and Cauliflower (Brassica) -- Ring spot (Black Blight)
 
Cause: A fungus, Mycosphaerella brassicicola, attacks cabbage, cauliflower, Brussels sprouts, and broccoli. The disease is a problem mostly with seed production. Seeds may carry the pathogen. The fungus also overwinters on infected weed and crop hosts or in residues. Spores spread by wind. Cool (59 to 70°F) moist weather favors disease development.
Symptoms: All aboveground portions of the plant may show symptoms. Individual lesions have dark concentric rings with definite edges surrounded by a yellowish zone. Under severe attack, spots coalesce, and the entire plant may be affected and blackened. In seed stalks, the fungus causes a distortion similar to the injury caused by the herbicide 2,4-D. Dark lesions may develop on stored cabbage and may penetrate deeply.

Note the dark, concentric rings surrounded by a yellowish zone.

 
Cultural control:
  1. Locate plant beds 1 mile or more from diseased fields.
  2. Burn straw stacks, and plow under diseased refuse of cabbage, turnip, and rutabaga seed fields immediately after harvest and before transplanting the new crop.
  3. Hot water seed treatment at 122°F for 30 min eliminates seedborne inoculum. Treat a small quantity of each seed lot, and test the germination before treating all the seed.
Chemical control: Some fungicides used to control downy mildew or white mold (see Cabbage and Cauliflower - Sclerotinia Stem Rot and Watery Soft Rot) also control this disease.

  1. Bravo Ultrex at 1.4 lb/A. 12-hr reentry.
  2. Cabrio EG at 12 to 16 oz/A on 7- to 14-day intervals. Do not make more than one application of Cabrio EG or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 0 day. 12-hr reentry.
  3. Echo 720 at 2 pt/A on 7- to 10-day intervals when disease threatens. Preharvest interval is 7 days. 12-hr reentry.
References:
Dixon, GR. 1981. Vegetable Crops Diseases. Westport, CN: AVI Publishing Co., Inc.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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