How to Grow Great Rape (Leafy Green Vegetables) in Zimbabwe

Monday, July 9, 2018


Rape (Brassica napus) is the most widely eaten vegetable in Zimbabwe. 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 sadza 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

Rape is a cool season crop; it is best suited to production in climates that are colder than those experienced in Zimbabwe.

It is typically planted in early February but April is considered the best time to plant it. It does best at temperatures of about 15-20 degrees C during the day and night temperatures of 10 degrees 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
    • 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. 
    • Hobson: This is a rape variety. It is dark green with large leaves and great taste. Resistant to powdery mildew.
  • Kale
    • Chou moellier/ choumoellier: a tall growing kale variety with a thick, fleshy stem. Hardy variety.
    • Thousand-Headed Kale: similar to choumoellier though the stem is not thickened. Tall, leafy indeterminate variety. Cold tolerant and hardy.
    • Curly Kale: Blue-green hybrid kale. Vigorous growth.
You can purchase rape and kale seeds from a number of seed suppliers including National Tested Seeds, Prime Seedco, Charter Seeds, K2 Marketing and Avanos Seeds.


Planting & 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 2-3 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 *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 three 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

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


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


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.

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.

Aphids: several species of aphids attack leafy vegetables such as rape and kale. Their plant sap-feeding can distort rape leaves and cause the leaves to curl. High infestation can cause a drop in yield and cause stunting. They also carry diseases. What to do: Dimethoate, Apron Star42M, Diazinon 30 EC or Disyston are effective. Apply Disyston 5% at planting time


Diseases

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.

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.

Damping off: seedlings are susceptible to damping off. The signs are rotting before the seeds emerge or topping over a few days after emerging. How to control: apply a seed protectant fungicide such as Apron Star 42 WS.

Practice Integrated Pest Management (IPM) to help reduce pests and disease these include:
  • removing all crop debris after harvesting
  • ploughing deeply to destroy or bury previous crop residue
  • selecting disease-free transplants 
  • practising crop rotation
  • keeping fields free of weeds as they are potential hosts of insect pests and diseases. 
  • ensuring that plants get optimal fertilisation
  • Using certified seeds
  • Using chemical control if necessary
Harvest & Post-Harvest Management


Depending on the variety and the conditions it is ready for harvesting about 4 weeks after transplanting and usually lasts for three months. Only mature leaves that are acceptable for market should be harvested.

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.

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.

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. Check ZFU Weekly Guides for price trends.

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