Black rot is a bacterial disease that affects crucifers (vegetables in the cabbage family). The bacterial pathogen, Xanthom*onas 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.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 13, 1999. The information contained within may not be the most current and accurate depending on when it is accessed.
Black rot is a name used for various diseases of cultivated plants caused by fungi or bacteria, producing dark brown discoloration and decay in the leaves of fruit and vegetables: A disease of the apple, pear and quince caused by a fungus (Botryosphaeria obtusa or Physalospora cydoniae)
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.
Use pathogen-free organic starting mix, and if you are adding compost, be certain that no diseased plant matter was used. Rotate with non-crucifers – Because the black rot bacterium can survive in debris in the soil, it is important to rotate away from crucifer crops for a minimum of three years.
Black rot is caused by a bacteria, Xanthom*onas campestris pv.campestris, that can infect most crucifer crops at any growth stage. This disease is difficult for growers to manage and is considered the most serious disease of crucifer crops worldwide (Figure 1).
Mancozeb, and Ziram are all highly effective against black rot. Because these fungicides are strictly protectants, they must be applied before the fungus infects or enters the plant.
Black rot spores love moisture, so you want to reduce the amount of moisture held in the canopy by providing great air circulation. During dormancy, prune heavily keeping only a few healthy, strong canes from last year's growth. Prune out any diseased parts of the vine too.
Other names for "pepper spot" include gomasho, meaning "fleck," and black speck, black fleck, black leaf speck, petiole spot, and vein necrosis. This disorder is cosmetic and has a negative effect on the appearance and marketability of the cabbage. It is safe to eat.
Cruciferous plants grown near infected plants and healthy plants handled with the same tools as diseased plants are at highest risk of becoming infected. How do I save a plant with black rot? There are no curative treatments available to combat black rot once the disease has occurred.
Spread within fields occurs via splashing rain, insects, wind-blown plant debris, or handling plants with infested tools or human hands. Warm (79oF to 95oF), humid or rainy weather favors infection and spread of black rot.
Disease development is favored by warm and humid weather. Symptoms of black rot first appear as small yellow spots on leaves. Enlarged spots (lesions) have a dark brownish-red border with tan to dark brown centers (Figure 1).
Thielaviopsis spreads in the soil and water via spores (conidia). Fungus gnats also help spread the spores. Due to its highly resistant overwintering spores, (chlamydospores), black root rot can be difficult to eradicate from a greenhouse with a history of the disease.
Black Fungus treatment usually includes antifungal medications. Medications like Posaconazole, Isavuconazole, and Amphotericin B can stop the growth of the fungus and bring the infection under control until the fungus is completely destroyed. In severe cases, surgery is done to remove dead or infected tissues.
The most obvious and characteristic leaf symptoms in the field are yellow 'V-shaped' lesions with blackened veins that develop from the edges of the leaves (Figures 1 and 2). As the lesions enlarge they become necrotic, pale brown and dry, due to blocking of the vascular system.
The best you can do is remove the parts of the plant that are dying (including the roots) and provide it with fresh soil. If the root rot is widespread and has affected most of the plant's roots and foliage, the plant may be beyond saving.
Symptoms. In the early stages, brown lesions appear on the plant roots then increase in size and turn black. Large areas, or all, of the roots are affected. Small roots are often completely destroyed.
Since black rot is a bacterial disease, fungicides are ineffective. Copper products are most commonly used, but overreliance on copper can lead to resistance.
Introduction: My name is Clemencia Bogisich Ret, I am a super, outstanding, graceful, friendly, vast, comfortable, agreeable person who loves writing and wants to share my knowledge and understanding with you.
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