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Expert says pesticides in growing managu should only be last resort

By Patrick Amunavi | Published Sat, August 4th 2018 at 00:00, Updated August 3rd 2018 at 23:40 GMT +3
Indigenous vegetable traders pack sagaa and managu at Magena market Kisii County. They source the vegetables from Nyangusu where large scale farming of the vegetables is done pack and transport them overnight to Nairobi. [Sammy Omingo/Standard]

Last week, we addressed environmental and ecological factors that support growing managu, this week we delve into tending to your managu to maturity to harvesting.

First, broad leaved nightshade is a heavy feeder and requires a lot of nutrients especially nitrogen.

Organic sources of manure are strongly recommended; poultry or farmyard manure could be used at the rate of 20-40 tonnes per hectare. Tithonia, dry leaf biomass at 2.5-5 tonnes per hectare can be used.

In the absence of organic sources, inorganic sources could be used: NPK, urea or sulphate of ammonia at 200 kg per hectare. These should be applied as side-dress two weeks after transplanting. Top dressing is required fortnightly or after every second harvest. However, care should be taken as too much nitrogen makes the plants susceptible to diseases and may lead to accumulation of nitrates to toxic levels.

Pests and Diseases

Leading horticulturalist Prof Mary Abukutsa says aphids, red spidermites and whiteflies are the main pests that attack broad leaved African nightshade “causing leaves to curl, stunt their growth and may transmit viral diseases.”

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To curb it, she recommends an integrated pest management system. Pesticides she says should only be used as a last resort because they often kill the natural predators, thus creating problems for the future. She notes that they are easy to get rid of by spraying with the right insecticide.

Diseases of potatoes and tomatoes like late blight, bacterial wilt and nematodes also attack the related nightshades so crop rotation is essential.

Cases where the soil has been affected by bacterial wilt, no Solanum crops should be grown there for at least three years.

Several indigenous methods of pest and disease control commonly used include use of wood ash on the leaves or the use of some plant formulations from Tithonia and neem tree. Try these before using chemical control.

Harvesting and post-harvest

The crop takes about four to five weeks from (Trans) planting to the first harvest and this can go on for up to 9 months.

To optimise leaf yield the lateral and main stems should be cut 5-10 cm from the tip to stimulate the development of side shoots, which are harvested in subsequent harvesting. Harvesting is done weekly or fortnightly. Ratooning can be done by cutting stems at 10-15 cm above the ground to allow new shoots to develop.

Picking should be done in the morning before the sun becomes too hot but after the dew has evaporated from the leaves, or late in the evening. With good management, leaf yield of between 20 and 40 tonnes per hectare can be obtained. Harvested leaves/shoots can be kept fresh for longer periods by wrapping them in bundles using plastic sheets, or can be solar dried and preserved for use during periods of scarcity.

Seed Processing

Mature berries of African nightshade are harvested and processed by wet seed processing method. The wet processing method entails, crushing  the fruits before or after fermentation, extraction of the seeds, separating seed from chaff then washing the seeds thoroughly before rinsing  several times to remove  growth inhibitors. The washed seeds should be dried under shed to remove surface water, then dry under the sun and ensure moisture content is about 8-10 per cent.

The dried seeds are then weighed and packaged.

Nutritional Value

African nightshade is grown for its leaves and shoots, and is used as a cooked vegetable often mixed with other vegetables. It is rich in vitamin A, vitamin C, protein, calcium and iron and has high anti-oxidant activity.

The presence of compounds such as phenolic compounds needs to be investigated further for their effects on the consumers for health and as anti-nutrients.

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