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Causal Agent: Bacteria (Xanthomonas campestris)

Symptoms: V-shaped necrotic lesions around the tip of leaves. Dark veins extending downward into the mid-rib. Cabbage, broccoli, cauliflower, kale, kohlrabi, Brussels sprouts, rutabaga, turnip, collards, radish, mustard, watercress, and other plants in the Crucifer (Brassica) family are susceptible. Vegetables other than crucifers are not susceptible.


Disease Development: The bacteria is know to survive from year to year and spread in a number of ways. Sources of infection include:

  • On/in seed
  • Nearby infected cruciferous hosts (ie weeds/volunteer plants)
  • Decaying crop refuse in the soil
  • Equipment/hands infested with bacteria

Plant to plant spread is usually caused by rain and irrigation splash and wind. Bacteria usually enter through natural openings called hydathodes at the tips of the leaves that function in transpiration. Wounds created by insects can also be a way in which the bacteria can enter the plant. Once inside the plant, the bacteria will work itself into the leaf, through conductive vessels, and into the main stem where it can work its way up and down the entire plant.

The disease develops best under warm, wet conditions. Temperatures of 80 to 86 degrees F favor infection and colonization. Free moisture, in the form of rain, dew, or fog, is required for infection to occur.

Control: Following the strategies below will reduce the incidence and severity of black rot.

  • Inspect transplants each day for black rot. If black rot appears on a plant, immediately removing and destroying that plant, as well as plants surrounding the infected plant for a distance of 3 – 5 feet has shown some benefit.
  • Purchase and plant disease-free seed and transplants.
  • Disinfest trays and boxes after use with a bleach solution.
  • Rotate away from cruciferous crops for 2 years or more.
  • Consider the use of direct seeding of crucifers in the field. This practice minimizes handling and exposure areas and reduces the chance of black rot spread, compared to transplanting.
  • Plant in fields with good drainage and air movement.
  • Irrigate from a well if possible. Well water tends to contain less contaminants.
  • Apply a balanced fertility program.
    • Excessive fertilizer causes rapid, lush growth especially when warmer temperatures arrive. The combination of lush growth and warmer temperatures are ideal for infection, especially when a rain or irrigation event occurs.
  • Control cruciferous weeds (i.e. Swinecress, Shepherd’s purse, and wild mustard/turnips).
  • Do not work field when plants are wet.
  • Use a copper containing fungicide.
  • Plow-in crop debris soon after final harvest.
  • Plant resistant varieties. This management practice has been shown to be more effective  than weekly applications of fixed copper or copper hydroxide beginning before development of symptoms. Resistant varieties have fewer infection sites and/or  the affected area is much smaller compared with susceptible varieties.

Hope you have found this information useful. Call me if you need anything!

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