Cabbage is one of the most important members of the cruciferous family, and grown extensively in Africa on a wide variety of soils. It is generally agreed that present-day varieties originated from the wild cabbage found growing along the chalky coasts of England and the Western and Southern coasts of Europe. Cabbage has been mentioned in ancient Greece and Egyptian literature and it was held in high esteem as a source of food. The cabbage has become one of the most important vegetables grown throughout the world, both commercially and in the home garden. Although cabbage can be grown throughout the year in most regions highest yields are obtained under cooler, winter conditions.
Figure 1 and 2: Cabbages growing in the field (left) and a cabbage ready for harvest (right)
The cabbage thrives under relatively cool, moist conditions and tolerates temperatures as low as – 3°C for a very short time but several days of very cold temperatures can induce ‘bolting’ to seed. Incidence of head bursting increases when very dry periods are followed by very wet periods, when accidental root pruning results from deep, adjacent hoeing or when excess nitrogen is applied after the head has already matured.
Irrigation is necessary to avoid excessive head bursting and ensure even and uninterrupted growth. Under warm summer conditions the plants are more susceptible to aphid attack, infestation by the cabbage moth caterpillar, both of which require regular insecticide control.
As cabbages are gross feeders, they require well-prepared and heavily fertilized soils high in organic matter and good water holding capacity. Soil tests should be carried out a few weeks before planting to determine the precise requirements for liming and fertilizer application. Cabbage grows best on slightly acid soils with a pH of 5.5 to 6.8.
For highest yields, growth should be rapid and uninterrupted. For a crop of top quality there should never be a lack of nutrients or soil moisture. A high level of nitrogen is the main requirement, followed by adequate levels of phosphorus, potassium and magnesium. There is usually sufficient nitrogen, phosphorus and potassium applied in compound fertilizers, together with side dressings of
nitrogen, but magnesium is often required in addition if the soil was not limed with dolomitic limestone. Boron deficiency will cause hollow stem and, if required, an application of about 25kg boron per hectare should be sufficient to correct any deficiency. Sulphur and molybdenum are also important micronutrients.
Since phosphorus and potassium move very little in the soil, these elements can be applied well in advance of transplanting time. Apply kraal manure or compost at 25 – 50 tons/ha, well worked into the soil, plus 100 – 150 kg Phosphorus per ha and 50 – 80 kg Potassium per ha, prior to transplanting. Alternatively, a compound fertilizer such as 2:3:2 can be applied at a rate of around 600 – 900 kg/ha, just prior toplanting.
About 4 weeks after transplanting, a side-dressing of 40 – 50 kg Nitrogen/ha should be applied and for varieties requiring a long time to mature, a second side-dressing of 20 – 30 kg Nitrogen/ha applied 8 weeks after transplanting. Liquid manure applications can replace these inorganic top dressings.
The most common method of production is by sowing the seed in specially prepared seedbeds and subsequently transplanting into the field. Seedbeds should not be made on the same soil more than once in 3 years. If root-knot eelworm is a problem, fumigation may be necessary.
Each bed is fumigated, normally using EDB or methyl bromide at each of 10 evenly spaced stations. This should be applied at 150 – 200 mm deep at a rate of 60 ml/m2. The soil should be damp to prevent the gas from escaping too quickly and the beds constructed so that they are 1 metre wide and 10 metres long. Each canister containing 480g of methyl bromide is capable of fumigating 10 square metres under plastic sheeting.
Prior to soil fumigation the seedbeds can be fertilized with kraal manure or compost at 3-5 kg/m2, or a compound fertilizer with the N: P: K ratio in the region of 1:3:1 with sulphur and boron component at 60 g/m2. After fumigation with methyl bromide the sheeting is removed and 2 days after treatment, the seed can be sown across the seedbed for a depth of 10 – 15 mm and the drills spaced 150 mm apart.
When the plants are approximately 30 mm tall a side dressing of 15g/m2 of the compound fertilizer can be watered in between the lines of plants.
Cabbage seed remains viable for up to 3 years after harvesting. Depending on the variety, 1 kilogram of seed contains between 280 000 – 350 000 seeds. 300 – 450 grams of seed are required to plant 1 hectare of cabbages.
At optimum temperatures between 20°C – 22°C cabbage seeds will germinate in 6 – 10 days. During periods of excessive heat the seedlings should be protected with a light mulch or shade for up to 2 weeks after emergence. This should be removed in time for the plants to harden up before transplanting.
Figure 3: A Seedbed
Figure 4: A Cabbage seedling ready for transplanting
The seedlings will be ready for transplanting when they are 100 – 150mm tall which is reached between 4 and 6 weeks from sowing, depending on the variety grown, prevailing weather conditions and age of the seed.
Cabbage plants grown during the hot, dry months of the year should be ‘hardened off’’ before planting into the field. ‘Hardening-off’ is primarily to condition plants so that less water will be lost from the cells of newly set plants and is achieved by withholding moisture for a few days prior to transplanting. The seedbeds are thoroughly watered immediately before transplanting. Wet sacking or newspaper can be placed at the bottom of the shallow trays or boxes. The cabbage seedlings dug from the seedbeds are placed on the wet newspaper and covered with wet sacking. Plants are then taken to the field and planted as soon as possible and watered immediately to avoid drying out the roots of the transplants.
Cabbages or crops in the same family i.e., Brassicae should not be planted on the same soil more than once in 3 years. This prevents the increase in the incidence of pests and diseases.
Table 1: Transplant Spacing for Cabbage Varieties
|Variety||Between plants (mm)||Between rows (mm)||Population per ha|
|Early||300 – 450||450||74 000 – 49 300|
|Mid-season||450 – 500||500 – 600||44 400 – 33 300|
|Late||450 – 600||750||29 600 – 22 200|
Only healthy and vigorous plants should be used, weak and sickly plants should be discarded. Transplanting should be done in cool overcast weather, or late afternoon.
Both practical experience and research results indicate that cabbages benefit from generous irrigation throughout the growing season. Heavy applications should be avoided once the heads have matured, to avoid excessive splitting. Ball-headed
cultivars are the most susceptible to splitting, followed by the conical cultivars and then the drum- head varieties. Most of the roots are in the top 600 mm of the soil. Soil-water depletion should not exceed 35 mm in sandy soil or 45 mm in heavier textured soils.
From the table below you can find an approximation of the frequency of irrigation, in days between applications, assuming that no rain falls in between applications.
Table 2: Approximate Frequency of Irrigation
|Assumed transplant date||First month after transplant (days)||Remainder of growing season (days)|
|Application of 35mm net per irrigation|
|Application of 45mm net per irrigation|
Figure 5: Irrigating cabbages
Cabbages are harvested as soon as the heads are sufficiently full and firm, as size increases very little once the heads are solid. If they are not harvested at this stage they will crack and go to waste if it should rain. Depending on cultivar, cabbages will take between 70 – 160 days to reach maturity.
Early varieties usually produce smaller heads. Harvesting is most often done by hand, cutting the head from the stem with a sharp knife. Cabbages should be harvested with 3 to 4 green wrapper leaves with the outer leaves being discarded. Improperly trimmed cabbage can be discounted by buyers on the local market.
The stumps of the plant should be removed to avoid aphid and other pest infestation. Stumps should be chopped and bruised before adding to compost heaps to facilitatedecomposition.
- Yield: Will vary considerably according to the variety grown, time of the year, and quality of seed, spoilage losses, soil conditions andmanagement.
- Usually, 30 – 35 tons/ha can be expected from older varieties although the newer crosses and hybrids produce yields in the region of 60 – 80tons/ha.
- Marketing and storage: Cabbages may be packed into clean bags, wooden crates or carted loose in lorries under tarpaulin cover. They are usually sold at the market in lots of 10 or 12 heads, in sizes of small, medium and large. Storage is feasible, but only for a period of a few weeks, at a temperature of7°C.
- WEEDS, PESTS ANDDISEASES
The elimination of weeds encourages rapid and continuous growth. Under summer rainfall conditions it is possible to use the weed killer Trifluralin (trade name Treflan) for the control of annual grasses and some broad-leaved annuals. Treflan is sprayed over the soil at 1.05 to 2.5 litres per ha, and worked into the soil by cross discing before transplanting. Hand weeding and mulching are more eco-friendlymethods.
This is a black and orange bug which causes leaves to wither. These are controlled by spraying Dichlorvos 5% at a rate of 200 ml/100 litres water or Parathion 25 WP at 125 g/100 litres water.
Figure 6: Bagrada bug
Apply Dimethoate 40 EC as a general cover spray at a rate of 75 ml/100 litres water or Metasystox
Bait made up of 100 kg of mealie meal plus 625g Endosulfan 50% WP should be applied to the ground before planting or close to the plants in the late afternoon.
Figure 7: Cutworm
· Red SpiderMite
This is a small orange to red mite with four pairs of legs of equal length. It spins fine webbing on the underside of the leaf. Silvering and mottling of the leaf results. Control is managed by using Asforaphin.
Figure 8 and 9: Red Spider Mite
· Diamond BlackMoth
These are small bright green caterpillars which cause a shot-hole effect in the leaves. Small, pale-green silken cocoons can be found. Control with cover sprays at regular intervals of no longer than 10 days using Endosulfan 35% EC at a rate of 700 ml in 500 litres of water/ha.
Figure 10 and 11: A diamondback moth larvae (left) and a diamondback moth (right).
This is a creamy pink caterpillar which feeds in the heart of the plant. Control as for Diamond Black Moth.
Figure 12 and 13: Webworms
Burrows into the leaves causing them to fall and/or become unsaleable. Control as per cabbage aphids.
NB: Careful attention must be paid to the instructions on the labels regarding handling and usage. The safety periods before harvest of any pesticides used on the crop must be observed.
· Bacterial BlackRot
Black rot caused by bacteria can be harmful during the rainy season or if an overhead irrigation system is used. Typical symptoms develop as tan-coloured v-shaped areas along the leaf edges, but necrotic patches are also produced in the main leaf lamina.
In both cases, leaf veins are darkened. Infection of the vascular system can extend through the leaf midrib into the main stem. When the latter becomes blocked, uptake of moisture and nutrients is restricted and plant growth very slow and eventually ceases. Spread of the infection is through infected seed, from plant to plant or from infected soil.
· Control for Bacterial BlackRot
Remove infected plant remains from the land and burn or bury on waste land. Do not feed infected plant material to animals as the infection can be spread through the manure. Use a seedbed site which has not previously been used for brassicas. Ensure soil fertility is adequate to keep plants growing rapidly.
Figure 14: Bacterial black rot
This is caused by a fungus which appears as a white fluffy fungal growth on the undersides of cotyledon leaves. Seedlings can be killed by the infection. Plants grown from brassica seed sown between February and April should be sprayed as a routine precaution. Infection of transplants and maturing plants shows as a small dark irregular marking, sometimes with a white fungal growth. The protection of seedlings is essential for healthy transplants.
· Control DownyMildew
Spray plants with Dithane M45 at 200gs /100 litres water every 7 – 10 days. Thoroughly spray or dip seedlings at transplanting in Dithane M45 or use copper oxychloride at a rate of 300 g/100 litres water.
Figure 15 and 16: Downey mildew on the to pside (left) and the underside of the leaf (right)
Cabbages are fairly sensitive to attack by various damping-off fungi. Seedlings assume the appearance of being pinched at soil level and collapse and wilt. Spread of the infection through the seedbed or seedbox can be quite rapid.
· Control for Damping-offDisease:
Sow seed thinly or thin-out seedlings at an early stage of growth, or drench the soil with Thiram at 10 g/5 litres of water each week. Mix seed with Thiram at 180 g/100 kg seed.
There are a number of varieties of cabbage available to both the gardener and commercial grower and vary according to the length of their growing season (days to maturity), shape of head and resistance to disease. Cabbages have either a flat round head; the drumhead type or a smaller conical head or roundedball-shaped.
Varieties are either pure bred strains or hybrids which are the first cross (the F1generation) between two pure-bred strains. Hybrids are generally higher yielding and more disease-resistant than pure- breds.
When cabbages are being grown on a commercial scale, the seed should be treated for Bacterial Black Rot as this is a seed-borne disease:
- Water is heated to 50°C and removed from the heatsource;
- The seed is placed in a cloth bag and immersed in the water for 25minutes;
- More hot water should be added to maintain the temperature at 50°C;and
- After 25 minutes at this temperature, the seed is removed, dried and dusted withThiram.
Several varieties of cabbage are available to the gardener or commercial grower:
Conical head type with various different strains. Top quality and colour but inclined to crack after maturing.
75 – 110 days to maturity. Resistant to Black Rot.
Figure 17: Cape Spitzkool (Conical shape)
Round, medium-sized heads; 110 days to maturity and; Susceptible to bacterial diseases
· Early JerseyWakefield
Early maturing good quality conical head variety; and Popular in the Western Cape of South Africa.
F1 hybrid ball-headed variety; 60 – 70 days to maturity; and Good resistance to ‘bolting’
· Glory ofEnkhuizen
Large, ball-headed variety; 75 – 115 days to maturity;
Fairly coarse in texture with pronounced ribs; and Heavy yields and good resistance to bacterial diseases.
Figure 18: Glory of Enkhuizen (large, ball-headed cultivar)
Early ball-headed type;
Short-stemmed, compact and light in colour; 65 – 90 days to maturity; and
Susceptible to bacterial diseases.
Figure 19: Golden Acre (Early ball-headed cultivar)
Red cabbage cultivar; Ball-headed; and
Slower to mature than green varieties with very hard and dense heads.
Figure 20: Red cabbage cultivar