Cabbage

Land preparation

The site should be ploughed to a fine tilth and removed with stones, weeds and debris. The ideal field for cabbage should have not been grown with other crucifer 1-2 seasons. The field has to be ploughed at a depth of about 15-20 cm, the debris removed, and then leveled. It is recommended to prepare land well before transplanting and avoid field operations when it is wet. This will help to prevent inadvertent spread of diseases from plant to plant and movement of infested soil within and outside the field.

It is preferable to plant cabbage seedlings on the plots, each having 1m -1,20m of width and a reasonable length with 40 cm width pathway.

Propagation in nursery

Site selection

• The ideal site for the nursery should be under the sun and not previously under crucifers, and preferably away from old crucifer fields. The nursery soil should be well aerated, drained and with good pH..
• The nursery soil should also be free from diseases and pests. It should be applied with well decomposed organic manure (5kg/m²) and the inorganic fertilizer such as NPK 17-17-17 (20 g/m²).
• The raised beds of 1-1.2m width and 20cm depth are made.

Sowing and nursery care

• The quantity of seeds required is 500g for 1ha (5g for 1 are). Care should be taken to buy non expired seed and this from credited sources/seed companies.
• During the day of sowing, the bed surface is leveled and sowing lines of 0.5cm depth are made using a stick. Seeds are sown in lines at the spacing of 10-15cm x 2cm and are covered with soil. Then, the much is applied on the bed, followed by regular watering. Alternatively, seed trays can be used to raised cabbage seedlings.
• Upon germination, the mulching material is removed. The seedlings should be protected from the direct sunlight.
• When seedlings are overcrowded in nursery bed, it is recommended to do thinning to allow light penetration.
• Fungicides like Mancozeb (2.5g/L of water) and insecticides like Lambda-Cyhalothrin (1m/1L of water) can be applied when necessary.
• To harden the seedlings, watering frequency is reduced and seedlings are gradually exposed to direct sunlight 1-2 weeks before transplanting.

 

Transplanting

Well hardened, 4-6 weeks old seedlings are ideal for transplanting.  Transplanting has to be done in early morning or late afternoon to avoid negative effect of direct sunlight on young seedlings.

Before transplanting, the seedlings are watered with enough water to avoid damaging the root system while uprooting. The seedlings are uprooted with a soil ball around the root system.

During transplanting, it is recommended to make 15cm deep holes at each planting point. Then, one handful of well decomposed organic manure is applied in each hole and mixed well with the soil. The organic manure required is 200-250 kg/are (20-25t/ha). The recommended spacing is 50 cm x 40 cm.

Fertilization

Cabbage is a heavy feeder with dense and shallow root system. In addition to 20-25 t of organic manure, a fertilizer dose of 180:50:50 kg NPK/ha is recommended.

Irrigation

To maintain growth, cabbage requires a consistent supply of moisture, and should as a general rule receive a minimum of 2.5 cm of water per week. Larger quantities may be required when cabbage is grown on sandy soils or when evapo-transpiration is high.  Heavy irrigation after a dry spell leads to quit firm heads and may burst or split open within 24hours.

Intercultural operations

Since most of the feeding roots are concentrated in top 5cm layer, deep intercultural operations are to be avoided. Providing organic mulch or black polythene mulch are beneficial for increasing soil temperature and to increase yield.

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.

Cabbage is often hand-harvested when heads are firm to the touch but before cracking begins. With hand harvesting, a given field is harvested two to four times to obtain heads of uniform size and maturity. Only one to three harvests of hybrid cultivars are required because of their greater uniformity. Use of uniform transplants and consistent growing conditions also helps reduce the number of harvests.

Yields will vary with the season of production, cultivar, and production system used. With proper management, cabbage can produce 25-30t/ha.

Management:

• Intercrop with onion, garlic, spider plant, coriander to attract natural enemies.
• Avoid too much N.
• Plant in a well prepared fertile seedbed to promote crop vigour.
• Keep the fields free of weeds and alternative hosts.
• Manage the field to favour natural enemies such as lady bird beetles and hover flies.
• Mulch with wheat/rice straw or clear/transparent polyethylene sheet as reflectors of UV light discourage aphids from landing on the crop
• Use overhead irrigation to knock aphids off the leaves
• For chemical control, spray insecticides like Cypermethrine, Roket,etc.

Diamond back moth (DBM) (Plutella xylostella)

DBM is a serious pest of Brassicas and attacks all Brassica species. A full grown diamondback caterpillar is about 1cm long.Young larvae feed on leaves, leaving intact parchment like epidermis. Growth of younger seedlings is inhibited and also produces holes in leaves.

Management:

• To control DBM in small size farms, cover seedlings with row covers (fine nylon mesh) to prevent moths from laying eggs on the leaves and or next to the plant.
• Intercropping Brassicas with repellent plants such as tomato, reportedly reduces DBM infestation in cabbage. When intercropping with tomato, the cabbage crop is planted 30 days after tomato.
• Biological control of DBM using parasitoid wasp Diadegma semiclausum has proven very effective in the highlands of Kenya, Tanzania and Uganda.
• Botanicals such as neem-based pesticides are very effective for control of DBM.
• Physical protection method: dense planting of maize or sorghum around the field like a fence may be effective because the insect cannot fly over the maize and sorghum.
• Chemical control: Cypermethrine based chemicals like DUDU-CYPER and ROKET (at 1ml/1L of water) may be effective. But insecticide application is less effective for egg, mature larvae and pupae.

Whitefly (Aleyrodes proletella)

Whiteflies (Bemisia tabaci, Trialeurodes vaporariorum and Aleyrodes proletella) feed on Brassicas. Adult whiteflies are about 1 mm long.

Management:

• In East Africa, whitefly populations on Brassicas usually do not build up to such an extent that control measures are required.
• Natural enemies such as ladybird beetles, predatory mites and lacewings can play an important role in reducing whiteflies
• Proper fertilizer application because application of high doses of nitrogen fertiliser favours development of the pest

Use mineral oils, neem products or spray with soapy water solutions

Post-harvest management