Cabbage and Cauliflower (Brassica sp.)-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°F to 70°F) moist weather favors disease development.

Symptoms All aboveground portions of the plant may show symptoms. Individual lesions have dark concentric rings, from black fruiting bodies, 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.

Cultural control

  • Locate plant beds 1 mile or more from diseased fields.
  • Burn straw stacks, and plow under diseased refuse of cabbage, turnip, and rutabaga seed fields immediately after harvest and before transplanting the new crop.
  • 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.

  • Cabrio EG (Group 11) 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.
  • Chlorothalonil formulations (Group M5) are labeled.
    • Bonide Fung-onil is available for home gardens. H
  • Miravis Prime (Group 7 + 12) at 11.4 fl oz/A on 7-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days. 12-hr reentry.
  • Priaxor Xemium Brand (Group 7 + 11) at 6 to 8.2 fl oz/A. Do not make more than one (1) application of any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 3 days. 12-hr reentry.
  • Quadris Flowable (Group 11) at 6 to 15.5 fl oz/A on 7- to 14-day intervals or Quadris Top (Group 11 + 3) at 12 to 14 fl oz/A. An additive such as crop-oil concentrate or non-ionic surfactant may be used. Do not apply more than one (1) foliar application of Quadris per season. Preharvest interval is 0 day for Quadris Flowable and 1 day for Quadris Top. 4-hr reentry for Quadris Flowable, 12-hr reentry for Quadris Top.

Reference Dixon, G.R. 1981. Vegetable Crops Diseases. Westport, CN: AVI Publishing Co., Inc.