Rape (Brassica napus) is the most
widely eaten vegetable in Zambia. Rape (Brassica napus) is a versatile leafy
vegetable that can be used in a variety of recipes. The most common way it is
prepared is by slicing it thinly then cooking them in oil with some tomatoes
and a pinch of salt. Rape and kale
are then enjoyed as a side dish with the staple pap and meat.
What makes this a must-have vegetable
in your garden or farm is that it can be grown all year round (though it is
better suited to the cool season), and it is a steady, high-yielding vegetable
that can guarantee you a constant supply of income. It is also suitable for
urban farmers because it requires limited space.
If you are ready to grow these luscious
green leafy vegetables then follow the guide below.
Climatic and soil requirements
It is typically planted in early
February but April is considered the best time to plant it. It does best at
temperatures of about 15 to 20°C during the day and night temperatures of 10°C.
Kale can withstand lower temperatures compared to rape.
While the cool season is the best time
to plant, rape can be grown year round though hot summer periods can be
challenging due to increased pest pressure.
Rape can be grown on a wide range of
soil types, but the best results are obtained on sandy loamy soils if they are
well drained and not subject to the high water table. The optimum soil pH range
is 5.5 to 7.
Choose a site with full sun for best
growth.
Varieties
Rape
1. Giant Essex English Giant: This is the
most popular variety of rape and is adapted to local conditions. It is selected
for its hardiness. It's dark green; provides immense growth and has large broad
leaves.
2. Hobson: This is a rape variety. It is dark green with large leaves and great taste. Resistant to powdery mildew.
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| Hobson |
Kale
1. Chou moellier/Choumoellier: A tall
growing kale variety with a thick, fleshy stem. Hardy variety.
2. Thousand-headed Kale: Similar to
choumoellier though the stem is not thickened. Tall, leafy indeterminate
variety. Cold tolerant and hardy.
3. Curly Kale: Blue-green hybrid kale. Vigorous growth.
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| Chou moellier/ choumoellier |
Planting and propagation
When choosing a site to plant your rape
crop practice crop rotations by not planting where other crucifers/brassicas
were previously planted in the past 2 to 3 years. Brassicas include cabbage,
cauliflower, broccoli
and brussel sprouts.
Prepare seedbeds for planting by
removing weeds and debris and ploughing and discing to a fine tilth.
The seed rate is usually 3 to 5kg/ha,
if sown in the seedbed the rate is reduced to 0.5kg/ha. Final field spacing
should be 75 to 150mm by 450mm. This is ideal if cultivation is to be done by
hand, but for tractors, the row spacing should be increased to 600mm the
seedlings are thinned when they are 150 to 200mm tall. The seed is planted 12
to 35 mm deep, depending on the soil texture.
Seeds germinate fast in about 4 to 7
days. If transplanting, seedlings are transplanted when they are about 15cm.
Transplant hardened seedlings when it is cool (early in the morning or late
afternoon) to avoid seedlings wilting.
Fertilization
Rape is a heavy feeder and responds
well to the application of well-rotted organic manure (e.g. chicken
or cattle manure),
supplemented with a compound or straight fertilizer. Soil
analysis is also
required.
Basal-dressing, Compound L (5:10:10)
700 to 800kg/ha, should be incorporated into the soil 4 weeks before planting.
Top-dressing Ammonium Nitrate (AN)
100kg/ha should be applied every 2 to 3 weeks from planting for 2 to 3 times.
This is because rape is continuously harvested and nitrogen contributes to good
yields.
Rape is sensitive to boron deficiencies
just like any other brassica, Borate can be applied at 20 to 40kg/ha with
compound fertilizer in the basal dressing.
Management
The crop should be kept weed
free, especially in the early days when competition for nutrients and space is
high. Cultivation must be shallow to avoid root damage.
Before planting the soil should be
brought to field capacity to a depth of 500mm since planting into dry soil
followed by irrigation
is seldom satisfactory.
As the crop is grown predominantly in
winter, irrigation is necessary. As a guide, the crop should be irrigated when
available soil moisture has been depleted by 50%. You can apply mulch to
conserve water.
Pest and disease management
Rape succumbs to most of the insect
pests and disease that attack other brassicas. Scout for pests weekly because
early disease detection helps with controlling pest and disease outbreaks and
reducing losses or yields.
Insect pests
1. Bagrada Bug: These are black and orange bugs that
suck plants causing the leaves to wither and young plant to die. They are the
most serious pests in brassicas. They can also cause plant stunting and can
turn leaves yellow with a rough texture. You control them by applying Dichlorvos
50EC.
2. Red Spider Mite: These are small orange to red
mites that cause silvering and mottling of leaves. You control them by applying
Endosulfan 35% EC.
3. Diamondback
Moth: Small bright green caterpillars causing shot hole on
leaves, small pale cocoons. What to do: Endosulfan 35% EC, Malathion 25 WP,
Orthene 75 SP, Tamaron 600 SL, or Bacillus thuringiensis are effective.
Bacillus thuringiensis, however, is the most effective.
4. Cutworms: These are greyish brown caterpillar which attacks the stem of the ground level in the seedbed or at transplanting time. The damaged plant wilts and withers. What to do: Apply Karate, Dursban 4 E or Dipterex 95 SP along the crop rows immediately after transplanting seedlings.
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Cutworm |
 |
| Aphids |
Diseases
1. Black Rot: Characterized
by tan coloured, V-shaped areas along margins, necrotic patches. It is common
in warm climates and prevalent during the summer rainfall period. What to do:
to avoid these farmers must treat seeds using a hot water treatment and remove
infected plants and burn them. Also, practice crop rotation and destroy all
crop debris post-harvest.
2. Downy Mildew: As a disease gives farmers problems. It is characterised by white fluffy fungal growth on the undersides of cotyledon leaves, can kill seedlings. What to do: Spray Diathane M 45 every 7 to 10 days. Practice crop rotation.
 |
| Downy mildew |
Practice Integrated Pest Management
(IPM) to help reduce pests and disease. These include:
1. Removing all
crop debris after harvesting.
2. Ploughing deeply
to destroy or bury previous crop residue.
3. Selecting
disease-free transplants.
4. Practising crop
rotation.
5. Keeping fields
free of weeds as they are potential hosts of insect pests and diseases.
6. Ensuring that
plants get optimal fertilization.
7. Using certified
seeds.
8. Using chemical
control if necessary.
Harvest and post-harvest management
1. Depending on
the variety and the conditions it is ready for harvesting about 4 weeks after
transplanting and usually lasts for 3 months. Only mature leaves that are
acceptable for market should be harvested.
2. Rape is
harvested continuously and yields can range from 25 to 50t/ha (fresh weight)
over the harvest period though they have been known to reach as high as 75t/ha
under optimal conditions.
3. Harvest early
in the morning or at dusk when it is cool. Harvest leaves individually by hand
by pushing leaves downwards and snapping them off or using a sharp knife to cut
the leaves away from the stem. Start with lower leaves first.
4. Do not leave
the leaves out in the sun after harvesting, place them in a cool area or take
them immediately to market. Traders typically spray cold water on the leaves to
keep them fresh. To package rape and kale for market bundle the green leaves
together in up to 35 leaves depending on the target market (retail or
wholesale). Discard any yellow or yellowing leaves.
Marketing
There is a steady market for staples such as rape. Prices are however highly volatile due to supply and demand. Look for markets (e.g. supermarkets, traders and wholesalers) before selling because rape is highly perishable. It can be sun-dried for value addition or to reduce perishability.
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