See:
Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Ringspot
Cause A fungus, Mycosphaerella brassicicola, attacks broccoli, Brussels sprouts, cabbage, and cauliflower. The disease is a problem mostly in seed production fields. 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.
Cultural control
- Locate plant beds 1 mile or more from diseased fields.
- Burn straw stacks, and plow under diseased 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
- 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 on 7- to 14-day intervals. 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.
- Strobilurin formulations (Group 11) are labeled for use. Do not apply more than one (1) foliar application of any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
- Cabrio EG at 12 to 16 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Quadris Flowable at 6 to 15.5 fl oz/A or Quadris Top (Group 11 + 3) at 12 to 14 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days for Quadris Flowable, 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.