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Black rot of Brassica crops

Quick facts

  • Black rot is one of the most common diseases of broccoli, kale, and other Brassica crops. 
  • It affects leaves, and often results in head rot. It can be severely yield limiting. 
  • A few cabbage varieties have some degree of tolerance, but for the most part, resistant cultivars are not currently available. 
  • Black rot is a bacterial disease that spreads through water. Managing water is key to managing this disease.
Up-close photo of cabbage leaves. There are V-shaped yellow lesions along the leaf edge that are becoming brown and necrotic.
Characteristic black rot lesions

How to tell black rot from other brassica issues

  • Initially, symptoms begin as yellowing at leaf edges, which turns into characteristic V-shaped lesions.
  • As symptoms progress, plants can develop blackened vascular tissue and head rot.
  • Plants can be affected at any stage of maturity.

Biology

Cabbage plant with rotting leaves and head.
Advanced black rot symptoms
  • Black rot is caused by the bacteria Xanthamonas campestris pv campestris.
  • This bacteria can infect any plant in the Brassica family, but tends to be most damaging in broccoli, cabbage, cauliflower, and kale.
  • Black rot often enters farms and gardens via infected seed.
  • Once present, black rot can persist in residues.
  • Bacteria enter plants through pores at the leaf margins called hydrathodes where dew accumulates in the morning. The bacteria can also enter the plant through infected seed, or wounds from hail damage, mechanical injury or insect feeding.
  • Some studies show that flea beetles and other insects may transmit the bacteria from plant to plant.
  • Black rot spreads easily by water.
  • Black rot spreads most readily in warm conditions (above 77 degrees F) with high humidity.

Managing black rot in the home garden

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Managing black rot on farms

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Author: Natalie Hoidal, Extension educator, local foods and vegetable crops

Reviewed by Marissa Schuh, horticulture IPM Extension educator

Reviewed in 2022

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