Pests and diseases management

Black rot (Xanthomonas campestris pv. Campestris)

Black rot is one of the most serious cabbage diseases during high rainfall and heavy dew conditions. The black rot bacterium can over-season on infected cabbage seeds, in weeds from the family Cruciferae or in infected plant material in the soil. Disease is common during wet conditions with high temperatures.

Symptoms:

• Yellow, brown or black v-shaped patches at the edge of the leaves. 
• In later stages, head turns black with an offensive foul smell. Bacterial ooze also will be visible on the surface of diseased tissue

Symptoms of black rot on cabbage

Management:

• Disease-free transplants should be used.
• Remove all infected plants and debris from the field and destroy by burning
• Spray the remaining healthy plants using a copper-based protective fungicide (eg. Copper-oxychloride: 250g/250ml water/has) to suppress further damage

  Bacterial soft rot (Erwinia carotovora var. carotovora)  

The disease may be found in the field, but is most severe during storage.  On cabbage, an initial infection occurs on the outer petiole (leafstalk) which is in contact with the soil, and then progresses to its head. An infected head is watery and often has a complete head rot. The affected area becomes soft and mushy and generally turns dark in color.

Photo. Cabbage infected by bacterial soft rot

Management:

• Plant on ridges or raised beds to prevent water-logging around the plants and respect crop rotation.
• Prevent other diseases (e.g. black rot; damping-off) or damage that may provide opportunities for soft rot to develop.
• Avoid harvesting when conditions are warm and moist. These conditions favor the development of soft rot.
• Harvest healthy cabbage heads first and store in a cool, dry, airy place.
• Wash hands and harvesting knives.
• Remove and destroy diseased crop or left over stems in the field after the crop has been harvested.
• Spray of fungicides including Copper Oxychloride (such as FUGURAN) at the early stage of head formation and after heavy rain is also recommended.

Downy mildew (Peronospora parasitica)

The characteristic symptoms are appearance of purplish brown spots on under-surface of leaves. Upper surface of leaves has lesions in tan (yellowish brown) to yellow color. Infection exposes heads to soft rot.

Photo: Symptoms of downy mildew on cabbage

Management:

• Destruction of diseased debris after harvest of the crop
• Spray the plants using Mancozeb or a copper-based protective fungicide at 15 days interval soon after appearance of the disease.

Cabbage Aphids

Several species of aphids attack brassicas in East Africa: the cabbage aphid (Brevicoryne brassicae), the false cabbage aphid (Lipaphis erysimi), the green peach aphid (Myzus persicae).  In particular, the cabbage aphid is a major pest in the region. Cool, dry weather is most favourable for aphid development. Large numbers of aphids may kill small plants. Their feeding can distort leaves of older plants and causes leaf curl.