Black Rot of Cabbage

Black rot is a bacterial disease that affects crucifers (vegetables in the cabbage family). The bacterial pathogen, Xanthomonas campestris pv. campestris, is particularly damaging to cabbage and cauliflower, but turnip, rutabaga, collard, kohlrabi, and Chinese cabbage are also susceptible. Broccoli is somewhat more resistant, and radish is usually highly resistant.

The first symptoms are usually yellow V-shaped lesions at the leaf margins. As the diseased area of the leaf expands and turns brown, the leaf veins in the affected area may appear black. Eventually, the leaf collapses. The pathogen may enter the stem and spread to all parts of the plant through the vascular system. Infected stems show a ring of black discoloration when cut near the soil surface. Black rot infection and spread is favored by wet conditions and temperatures in the range of 80-86 F. Crowded plants provide conditions that are ideal for bacterial spread to nearby plants.

To control black rot in the home garden:

  • Remove infected plants.
  • Remove any plant debris. (The bacteria can persist and overwinter in diseased plant parts.)
  • Fall tillage will help reduce the overwintering pathogen population.
  • Plant crucifers where air and soil drainage is good.
  • Avoid overhead irrigation if possible or water early in the day.
  • Use a 3-year crop rotation that excludes crucifers.
  • If infection is detected early, applications of copper may help reduce spread of the disease to healthy plants. However, copper products cannot cure diseased plants.

  • This article originally appeared in the August 13, 1999 issue, p. 109.


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