Olericulture (Compiled by Jennifer Tapedzisa)

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HORTICULTURE (Compiled by Jennifer Tapedzisa) Hortiuculture is a branch of agriculture derived from Latin’s Hortus colere meaning garden cultivation. It is divided into six branches:

1. Olericulture – science of vegetable production 2. Pomology – the science and art of fruit growing. Pome means fruit, and

ology means growing 3. Landscape/ornamental horticulture – primarily the art of growing flowers

and shrubs to beautify the landscape 4. Floriculture – cultivation, marketing and arranging of flowers and foliage

plants. 5. Viticulture – is the science and art of growing vines. 6. Nursery culture- Is the growing of horticultural crops seedlings for selling

purposes. The importance of Horticulture in Zimbabwe

Foreign currency earner. Creation of employment as the industry is labour intensive. Especially of

women who constitute the bulk of the unemployed in our nation (processing, marketing, agribusiness).

Some horticultural crops are of high nutritional value containing vitamins A and C; minerals like Fe and Ca; dietary fibre and are a source of energy.

Provides aesthetic value i.e in form of spices and colouring. Ornaments provide visual enjoyment by beautifying surroundings. Some horticultural crops are used for medicinal purposes e.g garlic thought

to control high blood pressure. Most crops are used in the manufacturing industry e.g insecticides

(pyrethroids), soups , stockfeed, perfumes, lotion etc. Promotes bilateral cooperation thru trading with other countries. Products sold highly competitive market- promotes spirit of

entrepreneurship: (no control on the marketing of horticultural commodities).

Contribution to GDP.

Characteristics of horticultural crops

Industry is capital intensive, complex and highly competitive. Intensive production on relatively small areas all year round. Products are sold in a highly competitive free market.

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Products are normally highly perishable because they have high water content are usually living.

Initial investment is quite expensive. Constituent water is essential to their quality. Generally grown more intensively and returns per unit area are normally

higher than with agronomic/forestry crops. Mainly consumed for the supply of micronutrients and vitamins and for their

contribution to flavour (spices) and interest of food (garnishing). They are generally not staple crops. Consumption levels depend on the selling price and the buyer’s income. Crops are normally traded in small quantities, in free marketing systems

where both supply and demand determine the price.

NB: CONSTRAINTS TO EXPANDED HORTICULTURAL PRODUCTION (own notes) Classification of horticultural crops Why classifying horticultural crops?

- There are many horticultural plants in the world. A lot of knowledge has been gathered on the plants. Classification makes summarisation of information on the plants possible hence serves time in information sharing

- It is an easy means of identification and communication on horticultural plants.

OVERALL CLASSIFICATION OF HORTICULTURAL CROPS

A) EDIBLES 1.VEGETABLES

1. Cole vegetables (broccoli, cabbage, cauliflower) 2. Legumes or pulse crops (bean, pea) 3. Solanaceous fruit crops (Capsicum pepper, eggplant, tomato) 4. Curcubits (cucumber, melon, squash and pumpkin) 5. Root vegetables (beet, carrot, radish) 6. Tuber vegetables (potato) 7. Bulb vegetables (garlic, onion) 8. Other vegetables (asparagus, okra, sweet corn)

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2.FRUITS 1) Small fruits

- Berries (blueberry, cranberry, strawberry) - Brambles (blackberry, raspberry) - Vines (grape, kiwifruit)

2) Tree fruits - Pome fruits (apple, pear) - Stone fruits (apricot, cherry, peach and plum) - Citrus (grapefruit, orange, lime, lemon, naartjie)

3) Herbaceous and vine fruits (banana, papaya, pineapple) 3.NUTS

1) Temperate ( pecan) 2) Tropical (cashew, macadamia)

4. HERBS AND SPICES 1) Flavourings (peppermint, spearmint) 2) Tropical spices (cinnamon, clove, nutmeg and pepper) B) NON- EDIBLES 5. ORNAMENTALS - FLOWERS, BEDDING AND FOLIAGE PLANTS

1) Annuals (marigold) 2) Biennials (English daisy, foxglove) 3) Perennials (daylily, rose, delphinium, iris, peony)

- Bulbs and corms (crocus, gladiolus, narcissus, tulip)

-LANDSCAPE NURSERY 1) Lawn and turf (Bermuda grass, bluegrass, fescue, perennial rye

grass) 2) Ground covers and vines (English ivy, Japanese spurge, myrtle) 3) Evergreen shrubs and trees

- Broadleaf (Holly, rhododendron) - Narrow leaf (fir, juniper and yew)

4) Deciduous shrubs (dogwood, forsythia, lilac, viburnum) 5) Deciduous trees (ash, crabapple, magnolia, sugar marple)

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VEGETATIVE PROPAGATION TECHNIQUES OF HORTICULTURAL CROPS

1. GRAFTING

Grafting is the art of joining separate parts of plants together so that they unite permanently and continue to grow as one plant

Parts of the graft Scion – this is a short piece of detached shoot containing several dormant buds in shoot grafting or a single bud in bud grafting, which when united with the stock, comprises the upper portion of the graft The scion is the source of characteristics such as; (i) Fruit quality, maturity time, disease and pest resistance (ii) Productivity, tree canopy shape

Rootstock/stock This is the lower portion of the graft on which the scion is grafted (attached) and develops into the root system of the grafted plants Rootstocks determine characteristics such as plant vigour, root system development, disease and pest resistance. Reasons for grafting

Preservation and perpetuation of clones not conveniently propagated by other means.

To obtain benefits of certain rootstocks and interstocks To change varieties of established plants To hasten growth of seedling selections To study viral diseases To repair damaged parts of trees To facilitate pollination of self-compatible trees by growing several kinds of

fruit on one tree Symptoms of graft incompatibility

1. Complete failure of the graft union to form 2. Very low percentage of graft success, poor off-take rates 3. The union occurs, growth occurs, but eventually the tree dies either in

nursery or in the field 4. Degeneration of tissues at the graft union, yellowing of foliage and pre-

mature defoliation




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5. Small stunted growth and general ill-health /poor vigour of the graft 6. Deficiency symptoms or nutritional disorders 7. Overgrowth or undergrowth of the stock or scion 8. Excessive swelling at the graft union 9. Breaking off of the tree at the union leaving a clean break

Conditions for a graft union to occur

1. The stock and scion should be in proper physiological state 2. The stock and the scion should be compatible 3. Ideal temperatures should be provided (7-32oC) 4. Cambium of the scion must be in intimate contact with the stock plant 5. Cut surfaces must be carefully protected from desiccation

2. BUDDING

Budding is a grafting technique in which a single bud from the desired scion is used rather than an entire scion containing many buds.

Budding is sometimes called bud grafting The major difference between budding and grafting is that budding

uses a single bud as the scion whereas grafting uses a piece of plant material that has several buds

Most budding is done just before or during the growing season. However, some species may be budded during the winter while they

are dormant. Budding requires the same precautions as grafting. However, budding is less involving and much easier to accomplish

than grafting Be sure that the scion and rootstock are compatible, the scion has

mature buds, and that the cambia of the scion and rootstock match. Special care to prevent drying or contamination of grafting

materials. With practice, the speed at which the process can be performed and

the percentage of successful grafts those that "take" - should equal or surpass those of other grafting techniques used on the same species.

Generally, deciduous fruit and shade trees are well suited for budding.

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Examples of budding are T-budding and patch budding

3. TISSUE CULTURE

The term plant tissue culture broadly refers to the cultivation in vitro of all plants

( single cells, tissues and organs) under aseptic conditions Plant tissue culture allows the propagation of plants from very small

numbers of cells within a tissue system or in the extreme case, from single isolated cells (protoplast culture).

There are various tissue culture techniques

Micropropagation Micropropagation is the application of tissue culture techniques to the propagation of plants starting with very small plant parts grown aseptically in a test tube or other container Micropropagation differs from traditional propagation in that the biological components of each procedure are separated into stages to produce a good degree of control over each aspect of regeneration and development processes. Micropropagation refers to in-vitro propagation of plants under aseptic conditions. Micropropagation can be described by four developmental stages namely:

1. establishment

2. multiplication

3. rooting

4. acclimatisation

Advantages of micropropagation

1. small pieces of plants are used to produce a large number of plants in a small space.

2. plantlets can be stored in vitro in a small area and less space and labour are required for the maintenance of stock plants

3. Plantlets produced are usually free of bacteria and fungi. In some cases they are virus free as well.




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4. nutrient levels, light , temperature and other factors can be more readily controlled to accelerate vegetative multiplication and regeneration

5. In most cases micropropagation is independent of seasons.

4. CLONING

A clone is a group of plants originating from a single individual and are propagated by vegetative means

Cloning is a powerful procedure both as a plant selection tool for breeding and as a plant propagation tool for reproduction.

Benefits of cloning Cloning enables the exploitation of a single superior plant with a unique

genotype Such plants maybe selected from a variable population of seedling plants,

from a single variant tree or branch with a group of vegetatively propagated plants

Population tends to be highly uniform phenotypically (all members having the same appearance, size, shape, blooming time etc) and this allows easier management

5. LAYERING

The plant part to be cut is rooted before it is completely cut away from the parent plant

Roots/stems maybe propagated by layering This method promotes a high success rate because it prevents the water

stress and carbohydrates shortage that plague cuttings

Examples: Tip layering Simple layering Mound layering Air layering Serpentine layering

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VEGETABLE PRODUCTION (OLERICULTURE) Site selection When choosing a site for vegetable production, it is important to take into account a number of factors which include topography, soil, climatic conditions, accessibility, labour and security.

I. Topography : the sited land must be fairly flat with the slope between 2% and 12%.

II. Water availability and quality: the site should be near an abundant, reliable and permanent source of water for irrigation. The water source should be tested for toxic materials such as excess boron, sodium, chloride and fluoride ions..

III. Soil : soil conditions need to favour crop growth for different vegetables. Fertile soils that are slightly acidic to neutral are best for most crops. Avoid saline soils. Deeper soils are more preferred than shallower soils. Avoid heavier textured soils as they have poor drainage and are difficult to work on when wet. Light textured soils have a poor water holding capacity and are prone to leaching.

IV. Climatic conditions – full sunlight facilitates growth of crops, therefore areas prone to shadows for most of the day should be avoided. Areas exposed to high winds are not suitable for vegetable production. Strong winds cause crop lodging. Dry winds during flowering will desiccate flowers and hampers bee activity resulting in poor fruit set. Avoid frost prone areas.

V. Accessibility - the area should be easily accessed for easy management. VI. Labour - the site should be where there is abundant and consistent supply of

labour at reasonable rates since vegetable production is labour intensive and requires proper timing.

VII. Security – the area must be secured against stray animals and unauthorized persons. The area must be fenced and where necessary bio-security measures must be put in place.

VIII. Land history – the previous use of the area should be considered. A previously dumping site of chemicals should be avoided.

CROP ROTATION -is alternating crops one after another on the same piece of land for maximum utilization. Principles of crop rotaion

Crops from the same family must not follow each other in a rotation. Crops that feed in the same root zone should not follow each other. A legume crop must included in the rotation Crops that are affected by the same diseases must not follow each other.




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Recommended rotation sequence is as follows: Fruit crop -------------legume-----------leaf--------------root/tuber/bulb Challenges of rotation in vegetable production

o Difficult to maintain soil fertility in crop rotation o Sanitation under irrigation is difficult to mantain. o Chemical weed control is sometimes difficult due to herbicide

persistence. o Labour available as well as labour skills available can determine the

crops to grow. o Market availability and prices can determine the crops to grow. o Climatic and water requirements differ per crop. o pH requirements differ with vegetables therefore sometimes difficult to

meet pH requirements of the next crop in the rotation. o Pest control difficult especially if an insect pest or diseases affect a wide

range of vegetables. o High cost of producing some vegetables may cause the farmer to opt for

cheaper vegetable not in the rotation plan. Drought alleviation strategies Many vegetable crops have high water requirements. When prolonged drought conditions occur, plan to conserve water and manage irrigation practices carefully. Use cultural practices that conserve soil moisture and allow plants to use water efficiently.

Reducing planted area may be ideal if irrigation water is in short supply. Select less drought sensitive varieties where possible. Consider transplants where less water can be used for irrigation. Use mulches and row covers to increase temperature for rapid plant growth.

Mulches can also save water by reducing surface evaporation. Maintain proper soil structure and fertility. Proper soil structure permits

infiltration and water holding. Proper soil fertility encourages the best plant growth and use of available soil moisture. Encourage soil organic matter accumulation to conserve moisture.

Good weed control reduces competition for soil moisture. Irrigation planning and management is generally critical for profitable vegetable production.

Good irrigation scheduling is essential for all irrigation systems to apply the correct amount of water at the correct time. Irrigation scheduling requires

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careful attention to soil type and moisture, crop growth stage, climatic conditions.

Drip or microjet irrigation is expensive but efficient system of irrigating high value crops. These systems may be combined with mulches and row covers for added efficiency.

1. CABBAGE PRODUCTION Family……………..Crucifereae Genus……………...Brassica Species……………..olereceae Sub species………...capitata Other members of the same genus

1. Rape…………………. (Brassica napus) leaves 2. Cauliflower………….. (B. oleraceae var botrytis) flowers 3. Broccoli…………........(B. oleraceae var italica) flowers 4. Chinese cabbage…….. (B. oleraceae var chinensis) leaves/head 5. Mustard ……………… ( B. oleraceae var juncea) leaves/seed

Origin Cabbage is believed to have originated from Mediterranean Center and Asia Minor. First consumed in 600BC. Some Brassicaceae crops commonly known as crucifers are widely recognised for their contribution to human nutrition and for other possible healthful benefits such as some crucifers may have cancer-preventative attributes Nutritional Values Component Value / 100g of cabbage Water 90g Carbohydrates 5g Proteins 1.5g Fibres 1.0 Fats 0.2 Vitamins 41.5mg Phosphates 0.28mg Calcium 0.24 mg Iron 0.05mg Uses Primary use is for salads but can be boiled or fried.




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Botany Cabbage is a shallow rooted vegetable to about 30cm with a short stem with compacted internodes. Early leaf growth is elongated and subsequent leaves are progressively sorter, broader and more erect. Leaves alternate and are folded together to form a rounded or conical head. Leaves are relatively thick but succulent. The leaf colour and head shape are variable depending with the variety grown. Varieties New varieties are continuously being produced on the market. These are some of the varieties already on the market: Star varieties, Drumhead, Marcanta (Blackrot tolerant), Hercules, Copenhagen market, Bardot (black rot tolerant). Climatic requirements Cabbage grows well in cool moist conditions with daytime temperature ranging from 16-24oC. The average minimum temperature is 4oC. Several days of cold temperature (-1 to 4 oC) induce bolting and production of seed. Temperatures greater than 25 oC adversely affect head density and shape. Dry spells followed by very wet conditions induce bursting of the head. Very hot dry conditions cause development of an undesirable bad flavour. Soil requirements Cabbage requires well drained fertile soils with adequate organic matter, slightly acidic soils with a pH of 5.5 - 6.1 (CaCl2). Soils with pH below 5.5 should be limed especially if clubroot disease is a problem. Soils should also have good water retaining capacity. Cabbage is fairly tolerant to soil salinity. Fertilizer requirements Cabbage is a heavy feeder and response well to organic manure which must be applied at least a month before planting to ensure decomposition. The crop responds very well to sulphur and is very sensitive to magnesium and boron deficiencies. Magnesium deficiency is shown by yellowing of marginal areas of leaf blades. Boron deficiency is characterized with hollow stems with brown necrotic areas. Soil analysis is essential to apply the correct amounts of fertilizers and lime. The following are general recommendations where soil analysis has not been done: Component Rate/Ha Organic manure 25 – 50t/ha Basal Fertiliser 1000kg/ha compound S/ Vegfert at planting Topdressing 100kg/ha of A.N twice at 3wk

Intervals. 1st application at 3 wks after transplanting. Boron Borate at 30 - 35kg/ha if deficient 3kg/m2 of manure

80g /m2 of basal fertilizer

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Seedbed Seed required to cover a hectare is 300 – 500g. If the seed is not certified, it may require Treatment in hot water at 50oC for 25 minutes, dried and dusted with 2g of Thiram/kg of seed to guard against black rot which is caused by Xanthomonas campestris It is recommended not to use the same seedbed more than once in 3yrs. Sowing depth of 0.5 -1.5cm is ideal. Seed may take 6 -10 days to emerge at a temperature 20 -22oC. Seedlings are ready for transplanting from 4-6wks after emergence at a height of 100 – 150mm. Transplanting should be done early morning or late afternoon. Spacing depends on soil type, size of the head and maturing time of the crop. Spacing Variety In row (mm) Inter row (mm)_____ Early season 300 – 450 450 Mid season 450 – 500 500 -600 Late season 450 -600 600 – 750 Watering Cabbage does well with generous irrigation throughout the growing season. Soil water depletion levels must not exceed 35mm in sandy soils or 45mm in heavier soils. Moisture stress should be avoided from head development until harvest as this will significantly affect the yield and quality of the cabbage. The evaporation rate can be more than 4 mm per day. 30-40mm of water can be applied per week. Crop protection 1. Weed control The land must be kept weed free by using either herbicides and or shallow cultivation to prevent root damage. Herbicides that can be used are:

Trif – 1 -2l/ha applied 14 days before transplanting, disced into the soil and remains effective for 4 months.

Alachlor (Lasso) – 4l/ha applied after 1st transplanting irrigation but before the weeds emerge and it is effective up to 2 months.

2. Insects pests Pest Damage Control Bagrada bug

Both adults and nymphs feed on the leaves and the leaves oftenly wilt. Young plants die out completely.

Dimethoate 40 E.C

Cabbage aphid

Suck sap on the leaves. Seedlings become stunted.

Dimethoate, Metasystox, Malathion




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Diamond back moth

Feeds on the leaves leaving the veins and the upper skin of the leaf resulting in a window appearance. The skin tears off as the leaf grow causing a ragged holey appearance.

Malathion 25 WP at 10 days interval, Endosulfan , Tamaron. DDvep

Webworm Feeds on the heart of the cabbage

Same as Diamond back moth

Leaf miner Burrow into the leaves leaving them not suitable for sale.

Carbaryl 85 WP

Cutworm Young larvae often feed on the leaves but older caterpillars feed at night at the base of the plant or on the roots or stem just underground. Seedlings are typically cut at the ground level. One caterpillar may destroy many seedlings in this manner in a single night.

-Spray with Fenveralerate. -Drench with Karate around the transplanted seedling. -use bait made up of 100kg of mealie meal and 625g of Endosulfan 50WP. Apply the bait on the ground before planting or near the plants in the late afternoon.

Red spider mite

Suck sap causing the mottling of leaves.

Dimethoate, Mitac, Dynamec, Dicofol in rotation

3. Diseases Disease Symptoms Control Bacterial black rot

Small water soaked brownish spots with chlorotic (yellowing) centre. They join together and cause interveinal

No curative chemicals. Use certified seed, rotation, seed treatment with Thiram, sterilize seedbed. Dip seedlings in

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necrosis of the leaf. Dithane M45 or Copper oxychloride at transplanting. Routine sprays with the above chemicals as preventatives

Damping off

.Patches of seedlings will collapse. Poor emergence.

Dress the seeds with Thiram. Avoid over watering. Routine spray with copper oxychloride

Downy mildew

White fluff fungal growth on the underside of the leaves which may later turn into dark irregular markings on maturing plants.

Avoid over watering, sow thinly, routine precautionary sprays with Dithane M 45.

Integrated pest management strategies 4. Physiological disorders Physiological disorder Cause Cracking Erratic supply of water; dry spells

followed by very wet conditions. Tip burn Inadequate calcium; sudden

increase in growth rate; variety Harvesting The crop is ready when the heads are sufficiently full and firm i.e. approximately 80-110 days after planting. This is variable with varieties. Delayed harvesting result in excessive stem elongation, loss of textural quality, and head bursting may also occur. During harvesting the stem is cut well below the base of the curd. 3 - 4 wrapper leaves are retained.

Yield Open pollinated varieties - 30 -35t/ha Hybrids - 50 -75t/ha Head weight including the wrapper leaves varies from 1 -5kg Storage and marketing Field packaging of individually plastic-film-wrapped trimmed curds is practiced in many countries but may not be necessary for product marketed close to production areas. The post-harvest life for cabbage is relatively good in terms of how long the product quality can be maintained. The crop can be kept for 3 -6wks at 0 oC , 98 – 100% relative humidity.




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2. TOMATO PRODUCTION

Family……………Solanaceae Genus…………….Lycopersicon Species……………lycopersicum

Tomato originated Mexico. Tomato is the second widely grown solanaceous vegetable after potato world wide. Other related crops are egg plant, irish potato, tobacco and peppers. The acid sweet taste and unique flavours account for its popularity and diverse usage. Tomato is high in pro-vitamin and Vitamin C content. Varieties There are two types of varieties i.e. determinate and indeterminate. Bushy varieties are determinate i.e. More compact and bear flowers from nearly every node. Indeterminate varieties grow taller and bear flower clusters at every third node. Varieties can be for fresh market (table) or processing (for canning and making of soups or sources) Soil requirements Tomatoes are grown successfully on a wide range of well drained soil types, from sandy to fine textured clays as well as in soils of high organic content. A Ph range from 5.5-7 is usually satisfactory. If the Ph is below 5, lime should be applied to neutralize the soil. Climatic requirements Day temperatures of 25-30oC with night temperatures between 16-20oC are optimal for growth and flowering of tomatoes. High temperatures at fruit ripening stage cause blotchy ripening. Low day temperatures reduce growth rate and can cause badly shaped poor quality fruits. Tomatoes are very susceptible to frost. Hot dry spells followed by heavy rain cause fruit cracking. Moist overcast conditions are ideal for fruit splitting, foliar and fruit diseases and delayed ripening. In Zim the greatest challenge is production of tomatoes in winter except in the lowveld as well as high humid summer months in the highveld. Fertilizer requirements Soil analysis is essential before any adjustments to the nutrient status of the soil. Generally the crop responds very well to manure applied at the rate of 25-50t/ha. In the seed bed, 1:4 compost to soil mix ratio is desirable. In the seedbed, 100-135g/m2 (4 – 5.4kg/40m2 ) Compound S (6: 17:6) is ideal.

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Compound S is used as a basal fertilizer at the rate of 1000-1500kg/ha. A third of the fertilizer is broadcasted and incorporated into the soil and the rest is banded. . Top dress with A.N and S.O.P at the rate of 100 - 150kg/ha. Begin top dressing when the 1st fruits are at marble size. This should be done at 2-week intervals. The numbers of top dressings will depend on the vigour of the plant. Seedbed The soil must be free from nematodes and diseases. Fumigate the seedbed using EDB to control nematodes. Seed is treated in hot water at 500C for 25 minutes if not certified. Dust with Captan or Thiram to reduce damping off and bacterial diseases e.g. Bacterial canker 120 -250g of seed is required for a hectare. This quantity can be sown on a 40m2 bed. The seed is sown to a depth of 10mm in rows that are 75-100mm apart and in row spacing of 50mm. seedlings sown thinly and removed weeds produce vigorous plants which are more likely to withstand pests and diseases. Water/irrigate immediately after sowing, thereafter water twice daily until germination. Between 25 0C and 300C, seedling emergence occurs in 6-9 days after planting. Tomatoes are susceptible to water-logging especially shortly after germination as excessive moisture is conducive to damping off and root rot diseases. Water/irrigate once in the morning, after germination and emergence. Older seedlings should be watered twice or three times a week. Under very hot conditions, the seedbed may be mulched or shaded to reduce soil temperature. The mulch should be removed gradually when the seedlings emerge. In some cases, pots and speedling trays are used in the production of seedlings. These methods are costly but seedlings are easier to handle and plants suffer less root damage at transplanting. On the seedbed, seedlings should be hardened by with-holding water for a least 1 - 2 weeks before transplanting. Seedlings are ready for transplanting 4-6 weeks after germination. Transplanting Seedlings are transplanted when they are 10 -15cm in height. Transplanting is best done in cool weather on an overcast day or late in the afternoon. Avoid transplanting when the leaves are wet as bacterial canker entry is greater under these conditions. Spacing depends on the growth habit, purpose of the crop, growing season and harvesting method. As a guide spacing is 300-600mm in row and 1500- 2000mm inter row. In rainy season, tomatoes can be grown on raised beds and ridges, whilst in the dry season they are grown in furrows or on flat ground. Watering Generally overhead irrigation encourages fruit and foliar diseases. Drip or flood irrigation systems are preferred methods. After transplanting, water immediately. A second watering is required at least 5 -6 days later. Once established, watering can be




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applied once every 6 -14 days depending on the soil type. Watering should be increased once fruit start to set. General management practices Mulching, pruning, frost protection and staking/trellising can be done to improve yield and or quality of tomatoes. Crop protection Weed control Weed control is important throughout the whole growing season. This can be done physically by hand hoeing or chemically i.e. by use of herbicides such as Trifluralin, Nitralin, Sencor and Fusilade forte can be used. Weeding should however be stopped after vines cover ground if the crop is not staked or trellised. Pest control Pest Damage Control Red spider mites Suck sap on the

underside of leaves causing them to be silvery and mottled. A splin fine web is seen on the underside of the leaf. Under heavy infestation growth is completely retarded.

Remove infested plants and burn -Avoid entering in free areas form the infested areas. - spray with Apollo, Dimethoate, Dicofol

Heliothis bollworm

Hollow out buds and fruits

Thiodan, Carbaryl, Endosulfan

Aphids Suck sap on the underside of leaf.

Thionex, Malathion, Dimethoate

Nematodes Cause root knots on the roots of the plants resulting in retarded growth.

-Rotation -Fumigation using EDB

Whitefly Suck sap on the underside of leaves.

Confidor. Actara

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Disease control Disease Symptoms Control Bacterial canker The leaves wilt

and rotting seen when leaves are cut off flash on the stem.

-rotation -hot water treatment of the seed. -destroy crop residues as soon as harvesting (sanitation) -avoid transplanting when leaves are wet.

Bacterial spot Dark brown raised pustules on the fruits which become sunken and scarby.

-rotation -Hot water treatment

Bacterial wilt Plants wilt suddenly, woody tissues turn brown and bacterial slime oozes out at the lower parts of the stem or the root.

-rotation -sterilize equipment using formalin. -destruction of crop residues.

Early blight Dark brown leaf spots with concentric markings appearing on lower most leaves at 1st. It causes defoliation while infected fruits show some damage on the attachment to the stalk.

-use disease free seeds. -rotation -destroy crop residues soon after harvesting -Spray with Dithane M 45 and Copper oxychloride during the early stages of growth at 7-14 days intervals. -Spray with curative fungicides e.g. Ridomil,




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Milraz Late blight -Grayish green

water soaked areas which rapidly turn black appear on the leaves. -Dark brown lesions appear on the stem. -large mottled areas appear on the fruit and will later turn brown as the fruit rots.

Same as above

Viruses Stunted growth with mottled leaves.

No cure. Control vectors such as aphids and whiteflies

Integrated Pest Management Physiological disorders Physiological disorder

Symptoms control

Blossom end rot Necrotic dark brown sunken area at the fruit blossom end. If severe, it can affect the whole fruit.

-Maintain steady soil moisture. -balanced fertilizer programme including Calcium Nitrate.

Sun scald Area of the fruit facing sun fails to turn red at maturity and turns yellow. In severe cases the area becomes whitish and flattened.

Stake or trellis the plants to avoid direct exposure of the fruit to sunlight.

Blotchy ripening Uneven ripening of the fruit

Stake the plants -to allow even light penetration. -control viral diseases.

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-balanced fertilizer programme including K.

Cat face Deformed fruits with deep cavities.

-resistant varieties

Cracking Fruits crack. -resistant varieties -steady soil moisture -balanced fertilizer programme with correct levels of Nitrogen.

Harvesting Harvesting commences between 2-3 months after transplanting. Optimum temperatures for fruit maturation and colour development are between 200C and 240C. Below 130C, fruit ripening is very poor and slow. At 100C chilling injury can occur. At temperatures greater than 320C or less than 100C, lycopene (red colour) synthesis is inhibited to a greater extend. Harvesting is carried out at various stage depending on season and market. The crop can be picked at the pale blossom end, pink blossom end, pink, ripe and red stage.

1. pale blossom end : When cream coloured streaks are noticed at the blossom end . At this stage the fruit will last a week or more before fully ripe.

2. pink blossom end: fruit has a pink colour at the blossom end. The fruit will ripen in 4 days.

3. pink stage: The whole fruit is pink and will fully ripen in a day or two after picking.

4. ripe stage: The whole fruit is red but still firm and must be marketed immediately.

5. Red soft stage (over ripe): The fruits are red and soft and are very difficult to transport.

Indeterminate varieties can be harvested up to 6 months depending on the management. Yield Can range from 75-100t/ha or even more. Indeterminate varieties grown in controlled environments such as green houses and tunnels can yield as much as 150-200t/ha. Marketing Tomatoes are graded after picking on the bases of size and uniformity of colour. The fruits should be clean and free from blemishes before being packed in trays, crates punnets or boxes. Storage




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Firm red fruits can be stored for 7-10 days at 5-70C with a relative humidity of 80-85%. POTATO PRODUCTION Family Solanaceae Genus Solanum Species tuberosum Origin Potato originated in the Andean Region of Peru. During its early introduction to European Countries tenant farmers and rural population were encouraged to produce potato because of ease of preparation, palatability and its nutritional value. Nutritional value Potatoes are a component of carbohydrates 18%, protein 2%, substantial amounts of minerals and Vitamin C. Yellow fleshed varieties contain some carotene. Toxic components Potato tubers contain toxic glycoalkaloids, alpha-solanine and alpha-chaconine. When tubesr are exposed to light, chlorophyll along with glycoalkaloids are synthesized. These compounds taste bitter and ingestione can cause illness and death in extreme cases. However, toxicity depends on the amount ingested. Mechanical injury also induces the formation of these substances. Botany Potatoes are dicotyledonous short-lived perennials that are cultivated as annuals for their edible enlarged underground tubers. They are both sexually (true potato seed) and asexually propagated (clonal system). The use of tubers (clonal system) remains the best method for potato production in Zimbabwe. Introduction Potato is a high input and a high returns crop. The success of potato production is use of quality seed at the correct time with the right growing environment and adequate management skills. The main factors determining potato yield are choice of quality seed, time of planting, fertilizer application, land preparation, planting method, irrigation and crop protection. Soil requirements Potato can be grown on a wide range of soils provided they are well-drained, deep medium textured loamy soils with good aeration.

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Potato can tolerate slightly acidic soils of pH 4.2 -5.0 Cacl2 but optimum pH is 5.0 – 5.5. if the pH is too acidic liming is encouraged on the preceding crop as application of lime just before planting the potato crop will affect the quality of the tuber. High pH promotes development of potato common scab. Climatic requirements Potato is a cool season crop very susceptible to frost damage. It performs well under warm day temperatures and cool nights. Optimum temperatures range from 16 - 200C. temperatures above 290C, tuber initiation is greatly reduced. Best tubers are formed at 180C. Long periods of high day temperatures >350C cause crop injury while high night temperatures are more often responsible for low tuber formation. Fertilizer requirements Pre-plant soil analysis is critical to estimate fertilizer needs. As a guide, the general recommendation of basal fertilizer is 1500kg -2000kg of Compound C or Compound S and top dressing 100kg – 150kg of Ammonium Nitrate. Apply all the basal fertilizer at or before planting as all the potash and phosphate should be applied at or before planting for maximum utilization. Basal fertilizer can be broadcasted or applied by banding. Banding is most commonly used and is cheap and fast. The fertilizer is applied in the furrow and is slightly covered before planting. When the soil is inherently fertile broadcasting can be used. Nitrogen can be split applied if there is a risk of leaching. 50% of the Nitrogen can be applied at planting and the balance as top dressing. First top dressing is done 2 3- weeks emergence or when the plants are 20cm in height and the last top dressing before ridging. Late applications of nitrogen may lead to physiological disorders such as hollow heart, secondary tuber growth and tuber cracking. Large of nitrogen will lead to rank growth at the expense of tuber formation. Land preparation Early deep ploughing up to a depth of 30cm is recommended to allow for deep root penetration and maximum decomposition of organic matter. Discing must follow to break big clods. At last a fine seedbed should be prepared as clods and stones cause deformation of tubers. Varieties Potato varieties differ according to their combination of characteristics; yield potential (low, moderate and high), maturity period (early, medium orlate), their purpose (eating, processing or both), disease and pest tolerance, tuber characteristics (skin colour, flesh colour dry matter content and tuber shape). Some of the varieties registered by the Crop Breeding Institute are Montclare, BP1, Amethyst, Pimpernel, Diamond, Jasper and Garnet. BP1




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It is the early maturing commercial variety (14 -15weeks) available on the market. BP1 produces many blue flowers. It also produces oval, smooth, white skinned and white fleshed tubers with shallow eyes and of excellent quality. It has a medium sprouting habit. BP1 is a good yielder, +/- 25t/ha both in summer and winter in all regions of the country. BP1 is moderately tolerant to late blight but very susceptible to early blight in summer. Montclare It is a late maturing commercial variety (17 -19weeks). Montclare produces many purple flowers but rarely gives berries. It also produces large, oval to pear shape, white skinned and white fleshed tubers. It is a good yielder, +/- 40t/ha both in summer and winter in all regions of the country. It has most tolerance to early and late blight. Pimpernel It is a late maturing commercial variety (17 -19weeks). Haulms (stems and leaves) are upright with a red tint. Pimpernel produces few purple flowers and sometimes with few berries. It also produces small to medium, oval shaped, red skinned and yellow fleshed tubers with deep eyes. Yield +/-20t/ha but has outstanding processing characteristics. It is the country’s first choice processing variety normally grown under contract with the processing companies. It has moderate tolerance to late blight and is fairly tolerant to viral diseases. Amethyst It is a late maturing commercial variety (17 -19weeks). Amethyst produces many purple flowers and gives a lot of berries. Haulms are upright with dense canopy of small dark green leaves. It also produces flat oval shaped, white skinned and white fleshed tubers with shallow eyes and rough skin. Sprouting is quick. It is a good yielder, +/- 35t/ha to +/- 60t/ha depending on the season in all regions. It has high tolerance to late blight. Presently is the most widely grown potato variety in the country. Garnet It is a late maturing commercial variety (17 -19weeks). It produces thin haulms with narrow leaves and white flowers. It also produces white skinned and yellow fleshed round and medium sized tubers. Garnet combines high yield and good crisping qualities therefore can be used for processing. It is a good yielder, +/- 26t/ha. Can be produced both under rain fed and irrigated plantings. It has high tolerance to late blight. Jasper It is a late maturing variety with upright haulms. It has white skinned and white fleshed round to oval tubers with shallow eyes. The skin has some roughness but the tubers have a good appearance. It has some tolerance to late blight and frost.

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The yield is +/- 30t/ha especially as an irrigated winter or spring crop. Diamond Diamond is a medium to early maturing variety with good tuber distribution and high yields. It has a vigorous growth and an open canopy. It has moderate tolerance to late blight but very susceptible early blight. Seed selection Potatoes can be grown from true potato seed but use of tubers remains the best method for commercial potato production. Potatoes grown from seed tubers (clonal system) have highest crop vigour, shortest growing period, the highest potential yield with larger tuber size when compared to the crops grown from true potato seed. The use certified seed cannot be over emphasized as uncertified seed is the source of viral and bacterial diseases. Good seed ensures good crop quality and good yields. Certified seed is normally packed in 30kg pockets with the label showing grower’s number, crop number, harvesting date and seed grade. Certified seed is never sold directly the producer’s farm, open markets or by dealers but only through certifying agent or identified market dealers. The seed should be purchased in time two months before the targeted planting time to allow for sprouting at the farm. Seed rate The seed rate is generally 2 to 2.5tonnes per hectare. The actual weight depends on the seed size. The smaller the seed, the less the weight. However, it has to be noted that there is no yield advantage to use small seed over large seed except under adverse conditions. Tubers smaller than 25mm diameter should not be used as seed for commercial purposes because the yield return does not make it economical. Sprouting Potato seed is usually sold unsprouted (dormant).the dormant tuber will start sprouting with time. The potato dormancy period is variety dependent and can vary in length. Sprouting is the breaking of the dormancy period and initiation of the germination process. This can occurs naturally with time or can be induced by several methods:

1. Seed is sprout by being placed in small wooden trays or boxes called chitting trays with dry finely chopped grass under warm conditions of 30 -350C.

2. Seed tubers are placed in an air tight room e.g. by covering them with a tarpaulin.

3. Seed potatoes can be dipped into a mixture of water and gibberrelic acid (G.A) for 10 minutes. They are taken out, dried totally and can be put in chitting trays or packed in pockets left to sprout in few days in a dark area. Make sure the pocket or tubers are not in contact with the ground surface. If temperatures are low, the air circulation should be limited to allow the temperatures to rise. This is the most common method being used in Zimbabwe currently.




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Well sprouted seed will ensure an optimum stem density (15 to 20 stems/m2) for high yields and good tuber size distribution. Not all sprouts planted will develop into main stems but generally 30% of planted sprouts will develop into main stems. Fumigation This is done to control nematodes. The soil fumigation with EDB is done 2-3weeks before planting. With chemical such as Nemacur and Temik fumigation is done at planting. Planting Potatoes can be grown with inter-row spacing of 50 to 100cm. Narrow spacing geives better stem distribution but makes it difficult to makes ridges. Standard spacing is 90cm between rows and 30 to 40cm within rows. After seed purchasing, sprouting, land preparation, fumigation, the following steps can be done. Steps for planting

o Open furrows and apply all the basal fertilizer requirements. o Slightly cover the fertilizer. o Irrigate to moisten the soil for planting. o Treat the soil with a nematicide if fumigation was not done before. o Place the seed in furrows at the determined spacing. o May treat the soil against white grub and wireworms. o Cover the seed to attain a flat surface. o Irrigate to field capacity o Cover all exposed seed tubers.

Planting times In Zimbabwe, potatoes can be grown throughout the year in the Highveld and Middleveld but it is important to avoid frost. In the Lowveld avoid planting in high temperatures. There are three common planting times in Zimbabwe:

1. summer crop Planting is done in November and the crop will be harvested between February and April. It is recommended to plant blight tolerant varieties as there are high chances of the disease during this period. Lifting and tuber storage may be difficult if rains persist to the harvesting period.

2. Winter (1st irrigated crop) Planting is done in February to April. Planting dates should be adjusted to avoid frost in frost prone areas. The chances of blight infection are still high and preventative sprays should be carried out.

3. Spring (2nd irrigated crop) Planting is done from late July to early August after the risk of frost has passed in frost prone areas. The crop if fairly free from blight but preventative measures should be taken. This is normally the highest yielding crop due to low disease pressure. In the Lowveld, harvesting should done early to avoid the high temperatures experienced in September and October which may affect tuber quality.

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Weeding and ridging The land must be kept weed free as potatoes are very sensitive to weed competition. As a shallow rooted crop, cultivation should be kept to the minimum. Herbicides can be used. Some of the pre- emergence herbicides which can be used are Lasso 48EC (Alachlor), Dual Magnum 960 EC (Metolachlor), Sencor (Metribuzin 480SC or 70WP). The use of herbicides should be according to the manufacturer’s instructions. The optimum distance between the seed tuber and the top of the final ridge should be around 20 -25cm. A well shaped ridge has a wide and round tip. Ridging should complete by the time plants are 25cm high. Earthing up effectively will reduce tuber greening, potato tuber moth damage and infection of tubers by late blight. Irrigation requirements The potato crop should be adequately watered from tuber initiation to maturity. Irrigation schedules should have small but frequent applications since potato crop is shallow rooted. Too much water soon after planting can cause seed rots due to oxygen shortage. If the crop is supplied with adequate moisture before tuber initiation, number of tubers will be high. Irrigation after tuber initiation increases tuber size while before it increases number of tubers. Water after tuber initiation must be avoided as the results in malformed tubers. Potato common scab is reduced if the soil is kept moist. A general guide to irrigation frequency and water requirements is given below: Soil type Hot month (days) Cold months (days) Water requirement (mm)Light 3 – 4 5 -7 30 Medium textured 5 -6 10 -12 40 -45 Heavy textured 6 -7 12 -14 50 -55 Harvesting Lifting should start when the tuber skin is no longer peeling off easily to reduce physical skin damage which will eventually reduce post harvest life. This can be achieved by leaving the crop in the ground 12 -15 days after 95% of leaf defoliation or haulm destruction. Haulm destruction can be done to achieve early harvesting (to target a good market) or when the severe attack of late blight if feared. Under normal situations, the haulms should be allowed to die naturally. Harvest when the soil is neither too wet nor too dry to reduce tuber damages. Generally potato tubers should be marketed unwashed but if they are to be washed, they should be thoroughly dried before storage as this creates conditions conducive for soft rots to occur. Harvested tubers should not be exposed to direct sunlight as they will “green” (accumulation of solanin) which is bitter, poisonous and eventually eating quality declines. Storage After picking, potatoes can be stored in small heaps for a week to allow for curing. After curing the potatoes should be graded according to size and quality before




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transportation to the market. Once harvested, potatoes will start losing weight and quality therefore long storage for potato is not encouraged. Potato should be kept under low temperatures, below the optimum for sprouting but sufficient to maintain life and avoid high rates of respiration which causes weight and quality loss. Potatoes for consumption need to be stored in dark, cool, humid and well-ventilated stores. Exposure to light must be avoided as it causes greening which indicates the beginning of the conversion of starch to sugars causing a decline in eating quality. Potato tubers can be dusted with Malathion 1% Dust at 25g/10kg. Common insects (pests) Insect Crop stage Damage caused Control measures Nematodes Planting ,

emergence, vegetative

Infected tubers have a blister like lumps orwarty appearance. Rotting of tubers before lifting or in storage in severe cases.

-use clean seed. -fumigate with EDB after land prep but before planting.

Whitegrub Planting Shallow holes on the tubers.

- treat the soil with insectide such as Dursban at or before planting.

Wireworm Planting Bores numerous small shallow holes on tubers and sometimes mines into tubers.

- treat the soil with insectide such as Dursban at or before planting.

Cutworm Emergence Chew through the stem and chop the stem at the surface level.

Spray with Carbryl 85WP, Karate 5EC over the crop at emergence.

Aphids Seed storage, vegetative

-Transmit viral diseases. -sap suck. -produce honeydew which will attract fungal development.

-encorauge development of aphid enemies such as ladybirds, hoverflies and lacewings by not using strong insectides. -chemical spray Dimethoate

Tuber moth Seed storage, emergence, vegetative, maturity,

Larvae tunnels between the upper and lower leaf epidermis eating

Destroy volunteer potato plants. -good rotation with non solanaceous plants.

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storage out the green matter. Larvae may tunnel into the stem. Larvae tunnels into the tuber releasing grey/white frass on the point of entry.

Always cover tubers with soil during growth. -do not expose harvested tubers overnight after lifting. -chemical control- carbaryl 85 WP, Tamaron, Dursban

American Leaf miner (Liriomyza spp)

Vegetative stage

Mines through the leaf causing thinner numerous mines than those of tuber moth.

Spray with Trigard 75WP

Common potato diseases Diseases Conditions

favoured Damage caused Control measures

Late blight (Phytophtora infestans). Greatly feared as it spreads very fast through the crop

High relative humidity with free water on the surface for 14 hours +. Develops rapidly at temperatures between 15 to 200C

-small brown leaf lesions with a pale green border. -foliage destruction in short time. -White mycelium may form at the edges of the lesions on the underside of the leaf.

-use of certified seed. -Plant less susceptible varieties. -Diseased plants should not form foliage on rubbish piles or in the open. -prevention is better than cure therefore chemical use should be started before disease appearance from 15cm height depending on weather conditions. -alternate fungicides to be used such as Dithane, Copper oxychloride, Ridomil Gold, Bravo.

Early blight (Alternaria solani) In Zimbabwe most problematic fungal disease than late

Temperatures between 10 – 350C

Early stage is characterized with small lesions with concentric rings

-use of certified seed. -Plant less susceptible varieties. -Diseased plants should not form foliage on




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blight because favours a wider range of temperature. Can cause a yield of 50% or more.

on the leaves starting on older leaves after flowering. Can wipe the whole plant depending on stage of infection and environmental conditions.

rubbish piles or in the open. -prevention is better than cure therefore chemical use should be started before disease appearance from 15cm height depending on weather conditions. -alternate fungicides to be used such as Score, Dithane, Copper oxychloride, Ridomil Gold, Bravo.

Common scab (Streptomyces scabies) Affect the quality of the tuber with no significant loss on the yield quantity.

High pH levels and dry conditions increase chances of the disease.

Tubers develop superficial tan to light brown lesions of various shape and sizes.

-Avoid infected soils as the pathogen affect many crops. -Keep the soil moist throughout the growing period. -Avoid high pH levels

Soft rots (Erwinia carotovora subsp carotovora) Very important potato post harvest disease that may cause losses up to 90 -100%. The bacteria that causes soft rot is normally found in the soil.

Wet and anaerobic conditions in the field often when water logged conditions occur. Too humid conditions in the storage room.

Tubers become soft, water soaked and cream coloured becoming darker later with a bad smell. Rots highly spread from one pile to another.

-ensure good drainage. Avoid water logged conditions to occur in the field. Quickly separate affected tubers from healthy ones in storage. Keep the storage area dry.

Viral diseases -The major potato viral diseases are potato leaf roll, potato virus A,M,Y,X and S, tobacco necrosis virus. -Of importance is potato virus Y

Most viruses require a specific vector for transmission e.g. aphids, nematodes, fungi.

Loss of crop vigour.

-Use of certified seed. -Control the vectors.

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because it is easily transmitted and cause serious yield losses. Potato pests (harmful insects and diseases) Potatoes are susceptible to many pests. Some of the diseases affect the quality e.g. late blight, scab and black leg. Some potato diseases are transmitted through air for example early and late blight. Some diseases are transmitted by vectors such as potato virus X and potato virus Y are transmitted by aphids. The use of certified seed reduces the incidences of pests and diseases. A good crop rotation sequence and frequency will avoid potato pest and disease build up. As a recommendation, potatoes should not be grown more than once in four seasons on the same piece of land. Within that rotation solanaceous crops should be avoided. These include egg plant, tomatoes, paprika and tobacco. The best way to manage potato other means. The following crop/land hygiene procedures are recommended:

o Burn all trash and tops from the previous crop. o Ensure correct rotation – to exclude other solanaceous crops that would be

host to potato diseases. With correct rotation diseases such as fusarium, rhizoctonia, verticillium and scab will be eliminated or greatly reduced.

o Avoid transmission of soil from one land to another on implements as much as possible.

o Destroy solanaceous weeds that are host to potato diseases and pests – both within and surrounding of the crop.

Physiological disorders These are not caused by pathogens therefore are not diseases. They occur because of certain prevailing conditions. Physiological disorder Appearance cause Hollow heart A hollow cavity formed

inside the tuber. Affected tubers do not have external symptoms and the disorder is only noticed after cutting.

Excessive enlargement of the tuber due to high temperatures during tuber development.

Knobbiness Misshapen tubers sometimes with a secondary growth.

Period of interrupted growth by high temperatures. -irregular supply of water.

Greening Tubers turn green with bitter taste

Exposure of tuber to direct sunlight during the




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growing period or in storage.

4. ONION PRODUCTION Family Alliaceae Genus Allium Species cepa Origin Onions were cultivated in India about 600B.C. The Greeks and Romans were using onion as early as 400 – 300B.C. introduction to Europe occurred about 500 A.C. Onion has been cultivated for many years for food flavour and also health and religious purposes. Nutritive value Yellow and red onion and shallots contain high levels of dietary flavonols and quercetin glycosides (about 200-1000mg/kg). These compounds have antibacterial and antifungal properties and other health benefits (Rabatzky 1997). In plants, the above mentioned properties form part of a defense mechanism to prevent microbial infection, “blood thinning” and repel some insect pests. Carbohydrates are present mainly in form os sucrose, glucose, fructose. Protein, fat and fibre contents are low. Onion also provides caloric energy to human diet. Green onion tops have a high pro-Vitamin A and fair vitamin C content. Use Onion is mainly used as cooked vegetable and significant amount are consumed raw in salads, sandwiches and many other dishes. Onion can be canned, frozen, dehydrated and dried and pound to make different soups. Botany Onion is a herbaceous biennial monocot cultivated as an annual. Each leaf consist of a blade and sheath, the blade may or may not be distinctive. The sheath develops to encircle the growing point and forms a tube that encloses younger leaves and the shoot apex. The leaf blades are tubular, slightly flattened on the sides, hollow and are closed at the tip. Climatic requirements Onions are a cool season crop that have some frost tolerance but are best adapted to a temperature range between 130C and 240C. Optimum temperatures for seedling growth are between 23-270C. At temperatures above 300C, growth is slowed. Day length influences bulb formation. Onion form bulbs faster at comparatively high temperatures. If the temperatures are too low, no bulbs are formed and this influences the incidences of bolting.

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Soil requirements Onion does well in a wide range of soil type from light sands to heavy clay loams, however best results are from fairly deep sandy loam soils. The soils should be well drained with an optimum pH of 6.0-6.8 (Cacl2). Onion is very sensitive to water logging. At low Ph Molybdenum deficiency occurs. However, onion is very sensitive to salinity. Fertilizer requirements The fertilizer recommendations given are just a guide line only. The crop reacts very favourable to kraal manure applied at the rate of 40t/ha. Application of manure however cause considerable weed problems and may lead to thick or bull heads because of late release of nitrogen. Preferably, kraal manure should be applied to the previous crop. Applied nutrients levels should be 100 -150kg N, 150-220kg P2O5 and 120-160kg K2O [per hectare. Adequate applications of phosphorus and potash are essential more than for most vegetables for rapid growth and high yield. Potash in form of Potassium Sulphate improves storage qualities. A top dressing using Ammonium Nitrate at the rate of 100kg/ha should be applied 3 -4 weeks after transplanting. A further similar top dressing may be necessary if the plants look yellowish. Excessive application of nitrogen must be avoided as this causes thick/ bull necks, multiple centres and even bulb splitting. With the use of mineral fertilizers alone, trace elements deficiency may be evident. 1. Zinc deficiency This is characterized by poor growth and the occurrence of bright yellow, clearly defined stripes which extend along the length of the leaves. In addition, the leaves tend to curl up from the tips. To rectify this problem, apply Zinc oxide at the rate 1kg/ha in 100 litres of water or Zinc max at 1litre/100 litres water as a foliar spray. 2. Boron deficiency This deficiency is indicated when the leaf colour changes to blue-green and later the leaves become yellow and mottled with distorted shrunken areas. The lower become stiff and brittle. The use of fertilizer mixtures containing boron will prevent this deficiency. Varieties Most seed houses have more updated information on varieties. De wildt, Dessex hybrid F1 and Early premium F1 are some of the early maturing varieties. Texas grano and Bon accord are some of the late maturing varieties Propagation There are three methods which are used for production of seedlings in onion production i.e. transplants from the seedbed, sowing directly into the land and use of sets.




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The use of transplants is the most common method of production used in Zimbabwe. When using transplants and onion sets, the initial procedure is the same. The seedbed must be well prepared with a very good tilth and be as level as possible because onions on high areas develop very slow, weak and are the first to be attacked by thrips. Seedlings in the low areas remain yellow and stunted and are prone to water-logging. The seedbeds should be about 10cm above the pathways and 1.2m wide and 15m long. Although, it is claimed that onion can be grown for many years on the same piece of land, the use of virgin lands or disease free site is recommended to minimize the chances of infection by Rhizoctonia or Fusarium. The seed rate of 2 - 3.5kg is enough to cover a hectare. For calculation purposes, 28g of seed contains 7 000 seeds. Apply 2kg of Comp S or L per bed. In light textured soils, a top dressing with 0.5kg of A.N per bed may be necessary at 1 -2 weeks after emergence. The seed may be sown 12mm deep or may be broadcasted at a rate 200g/20m2 bed. After sowing, the seed should be lightly covered and the soil must be kept moist by two light irrigations per day until germination is complete. Optimum temperature for germination is 240C. Seedlings will emerge 8 -10 days after sowing. Thereafter, reduce watering to once every three days. On light sand soils, it is advisable to mulch the seedbed soon after planting to maintain the surface moist. Seed is usually sown late February up to end of April depending on the variety chosen and the locality. 1. Transplants Seedlings must be hardened 2 weeks before transplanting. Transplanting is done 6-8weeks after emergence when seedlings are 5-7mm in diameter (pencil thickness). Rough grading is done where very big of very small seedlings are left out. Depending with the weed control method to used, the distance between rows should be 300-450mm and 50-100mm within the rows. Generally, wider spacing tends to produced big onions which may be undesirable. Seedlings are planted in shallow furrows because bulb development is reduced with deep planting. The seedlings are placed at a slant on the sides of the furrows and only the roots are covered with soil to a depth of 10mm. After planting, seedlings will lie flat for a few days and then start growing upwards. The onion grown by this method will be ready for harvesting 6 -8 months after sowing. 2. Onion sets The use of onion sets is another method of production which is used as a way of producing onions for winter market. Sets are small bulbs, their growth having been intentionally arrested for the purpose of resuming growth at a later period. Short-day varieties are commonly grown out of season i.e. during long-day conditions to produce sets. In Zimbabwe, onion for sets is sown early August up to mid September. This climate during that period induces early bulb formation. Plant competition in the seedbed limits the bulb size. The seedlings are left in the bed until they mature in December i.e. approximately 3 months.

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At maturity the leaves start drying from the tips and the weak stem collapses. When the majority of the tops collapse the bulblets are lifted. Direct exposure to the sun must be avoided as they are easily damaged. The sets are dried in a shade preferably on a half-inch wire mesh and then stored in a dry place. The dry roots and leaves are removed before planting out. Ideal sets must have a diameter of 15-20mm weighing 2 -3g each. Sets greater than 25mm are likely to be sensitive to low temperature and will prematurely bolt after growth resumes. Sets bigger than 40mm in diameter tend to produce a higher proportion of split bulbs. The sets are planted in the field at the beginning of February at the normal onion spacing of 300 -450mm between rows and 50 -100mm within the row. The sets are planted into shallow furrows. Sprouting starts after a few weeks and then they grow rapidly since the food reserves in the sets are high. Harvesting commences about mid June. NB: This method of onion production has problems of split bulbs, thick necks and uneven ripening causing the final quality of the onion to be comparatively poor. However, these onions are well accepted at higher prices because they will be on the market during the high shortage period. 3. Seed sown directly This method is commonly used in United States. Seed may be sown directly on land which is sprinkler irrigated. The crop matures earlier than with transplanted seedlings and there is also less premature bolting. Soil must be thoroughly and finely prepared for good germination. The soil must be kept moist until germination occurs. Sprinkler irrigation must be applied every two days in the field. Onion seedlings are extremely tender and will only develop normally when conditions are favourable in early stages of growth. Efficient small seeders can be used and seed rate is approximately 4 - 6kg per hectare. A uniform stand is desirable. Advantages of direct sowing are the elimination of transplanting labour costs, no transplanting shock and maturity is hastened. However, considerable labour is required for thinning. The thinned seedlings may be transplanted. If the onions are not thinned high yields may be obtained but the bulbs will remain very small. Time to sow The successful growing of onions depends mainly on the correct time of sowing. In the seedbeds, onions are normally sown between late January and end of April. Onions are grown during winter but bulbing will only occur from August onwards. Harvesting takes place form September to December. The tendency is to try to sow earlier but it must be appreciated that early sowing do not necessarily mean harvesting any sooner. Bulb formation is determined by day length and temperature; therefore the crop will only commence bulbing at the onset of spring. The warmer the spring, the quicker the crop matures. Irrigation




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Light irrigation should be applied daily after transplanting until the seedlings are standing straight (normally in 3 -5days). Thereafter reduce irrigation depending with the soil type. Water consumption is low in first 10weeks after transplanting but very critical during bulb formation. During this period, the crop must not be allowed to wilt. Total water requirement of the crop is 500 -600mm Crop protection Weed control Onions remain in the land for a long period and weeds can become a problem. Hand weeding is necessary in the rows as mechanical cultivation is often not practical because of the close spacings and that the soil should not be worked deeper than 50 -75mm. The most satisfactory method of weed control is by the correct use of herbicides. The following herbicides are registered in Zimbabwe for use on onions: Herbicide Time of

application Weeds controlled Remarks

Goal 24 EC Pre -emergent Annual broad leaf and some annual grasses. Can affect nutsedge.

Apply 10 -18 days after transplanting. White spots may appear on the onion leaves after application. 4 months persistence.

Ramrod Pre -emergent Annual grasses in seedbed.

Apply after the first irrigation. 6-8 weeks residual effect.

Afalon 50 WP Pre -emergent Most annual broad leaf and some annual grass weeds excluding shamva grass.

Use on transplanted or sets onion. Apply 5 -20days after transplanting. Do not use on seedbeds or where clay content is < 20%. Persistence is up to 3 months. Light irrigation or

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rain should follow soon after application.

Round up Pre- crop establishment

Non- selective No residual effect in the soil.

Gramoxone Pre- crop establishment

Non- selective No residual effect in the soil.

Pests Thrips It’s a sap-sucking pest that can cause severe damage in onion, especially poor crops. Plant growth is reduced with silvery colour of the leaf. Thrips normally hide in the youngest leaves. The mature thrip is yellowish-brown while the larva is light yellow in colour. They multiply fast in warm weather. Thrips can be controlled by Thionex or Thiodan as a full cover spray at 10 -14 day intervals, commencing at the first sign of infestation. Harvest interval is 10 days. Disyton 5%G applied at planting will prevent thrips. Diseases Disease Symptoms Control Downey mildew Patches of purplish-grey

spots on the leaves appearing a few days after raining or heavy dew. Spreads fast in humid, cool weather

Spray every 4 -7 days in cool, humid weather with Dithane M 45. Once the weather becomes dry, the spraying must be discontinued. Harvest interval is 14 days

Alternaria blotch Uneven white patches on the leaves which may later turn brown or purple. The patches will be characterized by concentric circles surrounded by black fungus spores.

In humid and warm weather, spray with Dithane at 7-14 day intervals.

Pink root The roots are pink in colous and are usually dead. Ultimate bulbs are usually small.

Rotation, especially of the seedbeds.

Fusarium bulb rot

Old plants tend to die prematurely towards ripening. The bulb will be rotten at the base to a watery-brown consistency and roots will be dead. High

-Rotation.




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temperatures with wet conditions promote the spread of the fungus.

White rot Bulbs rot at the base and roots die. Outer skin is affected and mycelia can be clearly seen between the infected skins. Cool temperatures and humid conditions promote the spread of the disease

Transplant disease-free seedlings. Seedlings should be dipped in a solution of Brassicol 75WP at transplanting. For sets wet the bulbs completely with the mix.

Harvesting Onion bulb continues to increase in size until the foliage collapses. At this stage, the bulb will be at its maximum weight. The collapse is caused by a weakening and shrinkage of the stem immediately above the bulb when the plant is mature. Harvesting must commence when >60% of the foliage has collapsed. The mature onion will keep better. Onions are usually lifted by hand. When the soil is dry a light irrigation prior lifting is encouraged. Drying/curing Following bulb harvesting, curing is important to improve post harvest handling characteristics. Curing enhances the formation of well-coloured intact outer skin. Onions for immediate sale are not dried and are usually marketed within a week of lifting. Onion for storage must be thoroughly dried. When the weather permits, the bulbs are dried in the field. This is achieved by stacking in windrows in the field. The foliage must protect the bulbs from direct sun. In the event of rain, these windrows should be turned to facilitate drying. Air circulation should be encouraged during this period. Moisture or sunburn can affect the outer skin tissues leading to poor bulb appearance and lower market value. Curing or drying can also be accomplished with forced circulation of warm (300C), low-humidity air through the bins or piles of onion placed on slatted floors for 12 -24 hours. Large piles should be avoided. Temperatures are then reduced to avoid dark colouring the bulbs. Best skin colour develops at temperatures between 24 -300C. During curing onions can lose as mush as 5% of initial harvest weight. Yield The world average yield of bulb onion is about 16t/ha, but with excellent management, yields of 50 -60t/ha can be achieved. In Zimbabwe, yields of 30t/ha are normally achieved with good management. Storage and marketing Storage extends the availability of bulb over long periods. Mature onion bulbs store best at or near 00C and at 65-70% relative humidity. Bulbs are stored on wire netting ensuring good air circulation. Depending with the varieties, cured onion can be stored for 3-6 months in a dry and well ventilated building. Care should be taken to protect onions from rain. Smaller onions tend to store better than big ones.

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However, there are possible losses which include sprouting and rotting if proper conditions are not met. Dry onion can be marketed in pockets while green onions are sold in bundles. 5. CARROT PRODUCTION Family umbelliferae Genus Daucus Species carota Sub/species var sativa Origin Afghanistan is considered to be the center of origin. Uses It has been first cultivated for medicinal purposes. It was first consumed in 600A.D. Carrot is a common root vegetable which is eaten fresh or boiled. Although infrequently used, young tender foliage is also edible as a cooked vegetable. Carrots are highly regarded for their nutritional value because they are important source of pro- vitamin A which is provided by the carotene present in carrots. The carotene can also be extracted for colouring margarine and also added to poultry feed to intensify skin and egg yolk colour. The carrot seed is extracted for flavouring. Climatic requirements Carrots are grown under a wide range of climatic conditions and can be produced all year round in Zimbabwe with optimum temperatures between 15 and 300C. Carotene synthesis is affected by temperature and is optimum from 160C -250C. The pigment synthesis lags behind root growth, a reason why young roots are pale in colour. At temperatures in excess of 250C, colour deteriorates. Under cooler conditions germination and growth are slow and frost may damage the crop as it approaches maturity. Bolting (production of flower stalk) may occur if the plant is exposed to temperatures of 5-140C for a considerable period. Soil requirements Deep well drained sandy loams are the best for carrot production. Carrots can grow successfully on soils with a pH range of 5.5 -7.0 on CaCl2 scale. Acidic soils must be limed in accordance with the recommendations based on soil analysis. Fertilizer requirements Carrots are heavy feeders and responds particularly well to potash and high organic matter but quality is affected if fresh manure is used as this causes hairiness and branched/forked roots. Heavy application of manure should be given only to the crop that precedes carrots. Fertilizer applications should be based on the soil analysis.




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However, as a guide, Compound D is applied at the rate of 600kg/ha, SSP 450kg/ha, MOP 100kg/ha. Fertilization is usually adequate when: 75-150kg/ha of N, 50 – 100 kg/ha of P and 50 – 200kg/ha of K is supplied. Carrots generally have a relative high uptake of K. excessive nitrogen application have a tendency to promote foliage growth compared to root enlargement. Top dressing is usually not required after planting, but only for carrots showing signs of nitrogen deficiency should be given 150kg/ha of A.N at 4 weeks after emergence. Varieties Most varieties differ in the morphology (shape and size). Different countries have preference for certain carrot types and root colours e.g In Japan, carrots are seldomly eaten raw, long reddish – orange coloured roots and cylindrical carrots are preffered. In Europe, relatively short, slender and yellow-orange preferred. In North America, long deep orange types are preferred. A good variety should have the following characteristics:

Uniformity Increased growth rate Good yield Improved flavour Resistance to bolting, cracking and pest.

Some of the varieties grown in Zimbabwe are: i. Chantenay (thick base and short)

ii. Nantes (slender and relatively short) iii. Oxheart (heart shaped) iv. Imperator (slender and long) v. Kuroda (thich and long)

Sowing Carrots are normally sown in-situ but in some cases, pre-germinated seed seeds are planted using water or gelly-like material as a carrier medium. Specialized planting equipment can also be used for precision planting using uniformly coated seed. Fine tilth seedbed is a must. Where there is soil crusting non-uniform stands are achieved. Sprinkler irrigation can be used to aid emergence, Spacing in-row is difficult to maintain at planting but later through thinning. To reduce thinning labour carrot seed and sand can be mixed at a ratio 1:6 by volume. The rows can be 300mm – 400mm apart and thinned 50mm -75mm within row. Emergence may vary from 7 – 20 days after planting. Early growth is very slow and the first true leaves may develop 3 -4wks after planting. Mulching of rows is encouraged under very hot conditions or during the period of heavy rains to improve germination. The mulch should be removed gradually after emergence.

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Irrigation Most carrots varieties require 30 – 50mm of water per week or 450 -600mm for a cropping season. Low moisture causes development of strong root flavours while high moisture causes roots to split or crack and inhibits colour development. Uniform moisture levels are important. Best yields and water efficiency is obtained whenever about 40% of available moisture has been depleted from the root zone. Weed control Slow growth of carrots during the early growth stage makes it a poor competitor with weeds. If weeds are left uncontrolled during this period, they may overwhelm carrots seedlings. Some selective herbicides can be used effectively for weed management. However, root damage has to be avoided during wed control as this may be the entry of some diseases especially bacterial disease e.g. bacterial soft rot. Disease control Disease Symptoms Control measures Alternaria leaf blights (Alternaria dauci)

Irregular brown spots with yellow centres on the leaves. Under hot conditions the disease can quickly kill the crop top.

Difficult to control once the disease has affected the crop. Routine sprays with copper based fungicides on weekly basis. - Use of clean seed. - Hygienic practices

Bacterial blight (Xanthomonas campestris pv carotae)

Yellowing of leaves from the oldest leaves upwards.

Hygienic practices. No curative chemical control. Hot water treat uncertified seeds at 510C for 30minutes.

Bacterial soft rot (Erwinia carotovora)

Affected roots develop into soft slime mass either in the field or in storage especially under warm humid conditions.

Ensure adequate soil drainage in the field.

Crown rot (Rhizoctonia solani)

Rotting of the stem and crop crown.

Sterilize the soil before planting. Seed dress with Thiram.

Powdery mildew (Erysiphe polygoni)

White coating of spores resembling white powder on leaf surfaces.

Do not grow carrots immediately after susceptible crops. Remove and destroy debris after harvest. Avoid dry conditions i.e. environment wet Spray with sulphur and copper based fungicides.




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Insect control Carrots are usually less troubled by insect pests than other vegetables, nevertheless, the following insects are known to cause substantial damage

1. Armyworm (Spodoptera spp.) 2. Cutworm (Agrotis ipsilon) 3. Mearly carrot aphid (Dysaphis foeniculus) 4. Nematode (Meloidonyne spp)

Harvesting Carrot harvesting is not determined by a clearly defined maturity stage. For various reasons, crops are often harvested before potential full root size or maximum yield is obtained. Depending on the variety and prevailing growing conditions, the period from planting to harvest can be less than 70 to more than 150days. Occasional roots are field stored and harvested as needed. Carrots for processing are grown for longer time to increase weight, colour, sweetness and dry matter. High dry matter is associated with better storage and handling. However, extensive delay in harvesting increases fibre. Both machine and hand harvesting can be done. For hand harvesting, strong and health foliage and soil texture are important features for efficient harvesting. Yield A yield of +/_ 25t/ha is achievable Storage and marketing Soon after harvesting, carrots are washed to remove soil from the roots. Carrots should be cooled to 10C or 20C as soon as possible to retain quality and reduce wilting especially for bunched carrots. Carrots store best at 00C and 95% RH. Sugars increase during cold storage. Film – packaged carrots can store 6-7 weeks under these conditions. Bunched carrots store poorly and roots lose firmness because moisture is extracted by the tops thereby reducing shelf- life to as short as 7 days. However, bunched carrots show freshness of the product provided the foliage is attractive and intact. Exposure to ethylene in storage results in bitter taste, hence carrots should not be stored together with ethylene producing commodities (climacteric fruits) such as apples, bananas, melons etc.

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6. PEAS PRODUCTION Family : Leguminosae / Fabaceae Genus : Pisum Species: sativum Origin Not known but among the first cultivated plants more than 6000 years. Uses Eaten as fresh and also can be frozen, canned and dehydrated. Wrinkled seed cultivars are normally frozen while smooth seeded ones are canned. Dried peas can be processed into soup powders. Nutritional value Peas have high protein content, good amino acid balance and high digestibility making them most ideal for animal feed especially dried peas. Europe (38%) and North America (28%) are the leading green pea producers. Dry pea production is more than three times that of fresh peas. Climatic requirements Pea is a cool season crop which can tolerate light frost before flowering young plants are more tolerant to low temperatures but susceptible to frost damage from flowering onwards. Germination can occur on a wide range of temperatures bur it best achieved at 200C. Peas are very responsive to temperature especially during vegetative phase. Vegetative growth is best at temperatures between 13 -180C. Temperatures >290C stops vegetative growth and cause flower abortion if these temperature prevail after flowering. General optimum temperatures for growth are between 7 and 240C. Flowering is accelerated by long day length. Soil requirements Peas can be grown on a wide range of soil types from sandy loams to heavy clays as long as the soils are deep and well drained. Poor soil drainage strongly impair productivity and increase susceptibility of peas to root diseases. A pH of 5.3 – 6.5 on a CaCl2 scale is acceptable. Fertilizer requirements




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As a guide apply 400 -500kg of compound D incorporated before planting to avoid direct contact of seed and fertilizer at planting. Top dress at 3 weeks after planting with 100kg A.N. nitrogen must be carefully managed to avoid excessive (luxurious) foliage growth which competes with pod and seed development. Varieties VARIETY SEED RATE

(KG/HA) TYPE DAYS TO

MATURITY Greenfeast 120 -130 Determinate 110 Lancet 110 - 170 Determinate 65 Centenary 110 – 170 Determinate 65 Dark Skin perfection 110 – 170 Determinate 65 Onward 110 - 170 Indeterminate 110 Sowing Peas can be machine or hand planted to a sowing depth of 30-50mm. Inter-row spacing 300 – 600mm and in-row spacing of 30-50mm. In temperate climates, peas are planted in spring or in late or early winter (if heavy frosts do not occur). In Zimbabwe peas are generally sown/planted from mid March- mid May. Late planted crop is severely affected by powdery mildew. Water requirements Peas have a relatively low moisture requirement (75-150mm) depending on the seasonal conditions. Peas are susceptible to lodging and excessive moisture, so water logging conditions should be always avoided. Critical water requirement periods for peas is just before flowering and during pod development. Weed control A pea plant is a poor competitor with many weed species unless given a headstart. Disease control Peas are affected by common fungal diseases such as powdery mildew, downey mildew, botrytis and fusarium root rot. Bacterial diseases such as bacterial blight and aphid-vectored viral diseases such as pea stunted virus, pea streak virus and pea seed borne virus. Crop rotation, controlling vectors, proper irrigation and growing the crop in cool temperatures will lower the disease occurrences. Insect control Insect pests which normally affect peas are cutworms, aphids, thrips and nematodes. The use of any normal control methods can be successful .

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Harvesting Peas can be harvested at different stages depending on the market targeted. The following are stages at which peas are harvested:

a. When pods are immature and succulent (both the pod and seed are edible). b. When pods are well filled and the seed is still soft and immature. c. When the seed have fully matured and dried.

As the seed matures, firmness increases and seed coat thickens and become tough. Sugars are converted to starch. Peas mature rapidly during high temperatures therefore select varieties and planting dates in order to predict harvest periods as well as to achieve. For most fresh markets, multiple harvests are made by hand labour. Although very labour intensive, hand harvesting minimizes physical damage and help to retain quality longer. Dry peas for processing can be machine harvested. Marketing and storage During marketing peas are retained in the pods and not removed until ready for preparation and consumption. When removed from pods, pods have a greatly reduced post-harvest life.




Olericulture (Compiled by Jennifer Tapedzisa)

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Transcript of Olericulture (Compiled by Jennifer Tapedzisa)