GRAPES (VITIS SPP.)
It is a temperate crop and therefore limited in production by tropical climatic factors. Grapes are divided into three main classes depending on their purpose for example, wine, raisin and table grapes. There are four groups of grapes; European, American, French hybrid and Muscadine., In Kenya suitable conditions for grape production are found in Taveta, Baringo, Machakos, Yatta and lower Thika; Timau and Meru North districts. Other favourable grape regions are Kibwezi and Naivasha.
Dodrelabi (Gras Colman)
It is a blue-black, very vigorous and productive variety with medium to large clusters. Berries are large, spherical to oblong. The skin is thin and medium tough. The pulp is sweet with neutral flavour. It is susceptible to all grape diseases.
Muscat of Hamburg
It is a blue-black variety of medium vigor and productivity. Clusters are medium and loose. Berries are ovoid in shape. The pulp is soft, juicy with a distant Muscat flavor.
It is a white variety with low vigour and medium productivity. Clusters are large, tapering, shouldered and fairly compact. Berries are medium sized and ovoid. The pulp is tender and fairly sweet with a delicate Muscat flavour.
It is a blue-black variety of medium vigour and high productivity. Clusters are medium to large, very compact and requiring heavy thinning. Berries are spherical and large. The pulp is juicy and of medium sweetness.
Muscat of Alexandria
It is a green-yellow variety of medium vigour and productivity. Clusters are large, scattered irregularly, short to medium in length. Berries are large and ovoid. The pulp is sweet with distant Muscat flavour. It is grown for table and wine purposes.
Grapes can be grown from sea level up to 1900ma.s.l
At least 500mm average annual rainfall is required for the crop to do well. Irrigation is used to start the crop since grape season starts shortly before the onset of short rains. An application of 25mm/week of irrigation water is recommended until the bunches break colour. Irrigation is withheld after the long rains to force the grapes into dormancy.
The crop will grow under a wide range of soils but does best in sandy loam to clay soils provided they are well drained. The soils should also be at least 2 meters deep and rich in organic matter.
Grapes require a combination of humid and cold cycles during the production season, a condition that makes it difficult for farmers in the tropics to grow them. They require daily mean temperature range of 18-240C. Hot sunny dry weather is essential during fruit development and ripening stage.
In Kenya, Dormex (hydrogen cynamide) is recommended for breaking dormancy enabling the vines to form fruit as it offers the same effect as that of chilling winter weather in temperate conditions, where grapes are widely grown.
Grapes are commercially propagated through cane cuttings. Poor vineyards may be improved through grafting. Root stocks should be tolerant to nematodes.
The nursery is prepared to a fine tilth well before the main pruning of the dormant mother vines. Ditches 20cm wide, 30cm deep and 1.5m apart are dug along the nursery field.
- One year old canes are selected from vigorous mother vines of consistently high productivity and quality during the dormant period for nursery establishment.
- The canes are cut to 30-35cm long cuttings.
- Make a base incision 2-3mm below the bottom node and a top incision 2-3 above the top node.
- Cuttings should be spaced at 15cm a part in the ditches.
- Trenches are filled with moist soil and the whole nursery irrigated regularly for faster establishment.
No fertilizer should be applied until the nursery is established as this may inhibit root development. Once the cuttings are established, top dress with CAN to encourage vegetative growth.
Keep the nursery weed free and control diseases and pests as they arise.
Land should be ploughed and harrowed well before planting. Remove all perennial grasses and sedges. Holes of 0.3 m x 0.3 m x 0.3 m are dug and the topsoil and subsoil is separated. Each hole is filled with 40 kg farmyard manure, 30 kg compost and topsoil. The depth may vary from 60 to 90 cm depending on the soil type. The recommended spacing of vines is about 2 to 2.5m between plants and 3m between the rows.
- Seedlings are transplanted after 1 year by lifting old rooting in full dormancy from the nursery towards the end of the cool period (August-September). Lift with most of the roots attached as much as possible.
- Select the strongest shoot and prune off the others.
- Trim off the top of the cuttings with the strong shoots leaving 2-3 strong buds and also trim off very long roots so that the cutting fits snugly in the planting hole.
- Add 120g of double super-phosphate or triple super phosphate and mix well with handful of topsoil.
- Fill the hole with water and when all the water is soaked up into the ground, lower the cutting carefully into the hole. Place the cuttings such that 2-3 buds are left projecting above the ground level.
- Fill the hole with moist soil and firm around the roots without bending them.
- Cover the projecting stump with a mound of loose soil. Irrigate the vineyard immediately, then at weekly intervals. New shoots emerge in 2-3 weeks.
Field Maintenance of young Vineyards
Irrigate once every 2 weeks when the vines are properly established.
Top dress with 200g/plant of C.A.N. around each plant base 3 months after transplanting.
Formative training and pruning
This is pruning and training in the initial stages to establish the desired shape for future production. Once a fully developed vine attains the desired shape, simple annual pruning is done when the one year old vine goes dormant.
Select the strongest, straight shoots and prune off the others as close to the plant base as possible. Pinch off the growing tip when it reaches the first wire of the trellis to cause new growth at the buds closest to the pruning wound. Select two of these and train them to opposite directions on the lower middle wire.
For “T” (pregola trellis) and the veranda trellis, as many shoots as possible are allowed to grow and run across the top of the trellis. For the “T” and Veranda trellis, the shoots are pinched at the midpoint of the space between adjacent vines to stop further terminal growth. This encourages the lateral shoot formation and the laterals form the future pruning and fruiting points.
The laterals are then trained to the top wires alternately for” T” trellis and across the trellis on opposite directions for veranda trellis. When these have grown to sufficient length, they are tipped to prevent excessive growth which would spoil the form of the vine.
This is done to support the vine framework, expose the foliage to the sunlight which improves quality and quantity of grapes and for effective pest and disease control. A wide range of trellising and stem systems exist. Large frame works are preferred but have high initial capital outlays. The trellis should be established one or two years after planting. The following four trellis types are currently used in Kenya:
- Peroldor “T” Trellis
Consists of 3 wire system two of which are strained at each end. A 1m long timber cross piece is attached to the top of an upright post of 2.9m above ground level. The other wire is strung on the 90 cm from ground level. The vine is trained as a two arm cordon along the lower wire and the laterals trained on the top wires alternately to give a V- shaped frame work.
- Veranda or slanting Trellis
Consists of a cross piece attached to the top of an upright post at a slant angle of 45-50o. The cross-piece is usually longer than 1.5m and is nailed and braced to the post such that 2/3 of it projects to the front. Wires are strung along the cross pieces at 27-30 cm interval. One wire being along the top of the posts, two at each extreme and additional wires in between. The vine is then trained up to the middle wire and arms trained along this wire on either side of the trunk .The arms can then be bent over the secondary wires thus lengthening the productive wood on this system. Laterals are trained across the wires in the same direction as the cross-piece. The bunches will then hung down and be protected from sun scorch by the foliage
- Double veranda
The veranda system is modified to give a veranda on either side of the posts. It is more elaborate and difficult to work with but out yields the simple veranda system.
Overhead or Pergola
Two strong posts are erected and connected at each extreme end of the two rows. Intermediate posts are similarly erected if the rows are long. A metal cross piece is attached to join the two posts at each extreme end. Other posts are connected with strong timber pieces. High tensile strength steel wires are then strung at intervals of 30-45cm across the piece.
Standard dimension for this structure are:-
Vines spaced at 3 x 3 or 3 x 4m. Cross pieces should be 3-4m long. Height of trellis from the ground should be about 2m with a post at every fourth line. Cedar posts are recommended as they are relatively resistant to pests and weathering. Vines are trained to the trellis by a string of sisal twine from the base of the vine to the wire above. By means of this string, the vine is trained across the wire framework. Vines from the two rows should meet and cross on top of the trellis. As many arms as possible are allowed per single vine to evenly cover the available trellis space. Bunches will then hang down and be protected from sun-burn and bird damage. This is the most elaborate and expensive method of trellis.
Field Maintenance of a mature orchard
Laterals formed on the horizontal arms during formative pruning are used as bearers for succeeding seasons. At dormant pruning, these are pruned either as long or short spurs depending on the vigour and fertility of the vine. The first two or three main buds on the laterals are generally unproductive on most varieties. Shoots are therefore, generally pruned longer than three buds for fruit production and if necessary pruned short to produce vegetative shoots for the following season.
i). Green pruning and tying:
Under favourable conditions the shoots after bud break grow rapidly. There should be skilled personnel to attend to many tasks in the vineyards. Growing shoots should be spread evenly on the trellis to eliminate crowding and consequent disease. This is done by tying the shoot at reasonable intervals with sisal twine and removing of tendrils which are a nuisance when entangled with foliage.
When shoots reach a reasonable length of about 1 m, they are topped to prevent further terminal growth. This encourages an increase in size of bunches. If vegetative growth has been excessive, the lower leaves near bunches are removed to open the canopy and facilitate easier blooming and pollination and discourage disease development. Excess shoots should be thinned off in cases of favourable bud break.
ii). Bunch tipping and berry thinning
Some varieties form long clusters. The tip of the bunch should be cut before blooming to encourage better fruit set e.g. in Dodrelabi. In varieties forming compact bunches, berries should be thinned by use of blunt scissors at an early age to improve berry size and grape quality.
Later thinning should be done for all diseased, scarred and sun burnt berries. The varieties such as Office Vine and Golden Muscat need heavy thinning while Dodrelabi requires light thinning.
The following points should be considered while pruning.
- i) Pruning is done to balance wood and fruit production in the following season.
ii). As much wood as possible should be left as spurs to produce a balanced vegetative and fruit growth in the following season.
iii). The healing capacity of the vine is generally low and therefore cuts should be made as small and as clean as possible at right angles to the stem about 1.0cm above the top bud.
iv). Cover large wounds with grafting wax or bordeaux paste to prevent excessive loss of moisture.
- v) Remove all pruned parts from the vineyard to discourage pest and disease build up.
Irrigation is necessary and flood irrigation should be used once the berries break colour to avoid wetting of foliage and bunches.
Employ bird scarers from when bunches break colour to harvest. Use of fish nets, bird proof wire cages or perforated paper bags is encouraged where costs are not prohibitive.
The main plant nutrients should be applied regularly to maintain a high level of production of quality fruit.
i). Organic Matter
Organic matter is applied as manure or compost and spread immediately after harvesting. Up to 30 tons/ha can be applied.
Quantity to be applied depends on age and cropping pattern of the vine. Apply 400-600g of CAN in 2 splits for vines over 3 years old; one application after dormant pruning just prior to bud break and the second after harvest. For a heavy crop set, a light application of urea (130 g/plant) is made during berry set. Nitrogen should be applied in the form of urea and irrigated into the ground immediately after application. Over application of Nitrogen causes the plant to have more leaves than the fruit set, while under application results in low yield.
Promotes vigorous and strong root growth and hastens maturity. Phosphorous should be applied at planting time as 125g Superphosphate per plant (200kg/ha) in the planting hole. Top dress with single super-phosphate 200-400gm per plant, (300-600 kg/ha) after dormant pruning and work this well into the root zone. Regular use of farm manure or other organic manure facilitates the utilization of top dressed phosphorous. Leaves with bluish green colour with a dull tint at the edges are symptoms of phosphorous deficiency.
It influences fruit production and quality especially sugar and acid content. About 100g of muriate of potash per plant (160-200kg/ha) should be applied from the 2nd year onwards. This is applied at the time of pruning.
Disease and pest control
A routine spray programme should be started and repeated once every 2 weeks as soon as new growth emerges for the three major vine diseases.
|Disease and causal agent||Symptoms / Description||Control|
|Powderly Mildew (Uncinular necator)||There is an easily visible powdery coating on the underside of leaves and on bunches. This causes curling and shriveling of leaves which later die. The berries may also crack, resulting into total crop loss if the disease is not controlled.||The fungus can be controlled by spraying with fungicides such as Bayleton WP 25 as a full cover spray initially. Additional control measures may be required for some varieties.Planting resistant varieties|
|Anthracnose (Elsinoe amphelina||Causes small greyish black lesions with depressed centres and raised borders on shoots, tendrils and clusters. Isolated leaf spots are pale grey with reddish brown or purple borders. Spots enlarge and remain round or greyish at the centre with dark borders.||Use recommended fungicides as soon as the new growth emerges e.g. Dithane M 45, Zineb, or Antracol as soon as the new growth emerges.|
|Downey mildew (Plasmopara viticola)||Attack leaves at the centre of the vines. Initially light translucent spots form on the upper leaf surface followed by white powdery coatings on the underside of leaves. Seriously affected leaves crumble and fall off the vines. Flowers and young clusters may be attacked and destroyed and later drop off the vines. Infested berries wither, turn brown and finally shrivel falling off the clusters.|| Control as in Anthracnose
|Systates Weevil (Systates spp)||This is the major pest and usually hides in mulch or cracks in the trellis posts and emerges to eat young stakes used to train or trellis the buds and leaves at night.||Avoid mulching the vinesRemove all bark from posts and stakes used to train or trellis the vines.
Use suitable insecticide such as. Dursban 4EC as a foliar spray and around the base of the stem and mulch just before on-set of rains.
|Termites||These eat cuttings in the nursery and the vines that trail along the ground.||Mix Dursban 4EC with water then drench the soil. Pour the solution into each termite nest.|
|Red mites (Tetranychus urticae)||These attack the vines late in the season when the vine is approaching dormancy.||Use recommended miticides e.g. Kelthane, Dynamec 1.8EC, Mitac EC, Binapacryl, Omite as soon as the first sign of the attack is seen.|
|Scales (Parthenolecanium persicae)||This attack the plants causing sloughing off of the bark and may completely kill the vine. Scale excretes honeydew, which falls onto grapevine leaves and bunches leading to sooty mould development leading to reduction in growth and productivity||Prune off dead or affected parts and burn.Use recommended insecticide such as BASUDIN 600 EW|
|Systates weevil||Weevil damage|
Powderly Mildew Bacterial blight (grapes leaves
Bacterial blight (grapes stem) Grapevine scale tended by ants.
Grapes are harvested when bunches are ripe and after a uniform colour. The sugar content should be close to the maximum attainable for a particular cultivar and the acidity is low at this time. The characteristic flavor should also have been developed. Fruits do not ripen after harvesting. Harvesting should be done in the morning by cutting bunches from vines, leaving stalk for easier handling. Depending on the vine variety, density of plantation and pruning scheme, yield could range between 5- 20 tons of grapes per ha.
Place bunches in trays lined with tissue paper and deliver to packing shed. Discard diseased, damaged, unripe and malformed berries. Clean and rinse the bunches with clean water and drain of the water. Pack the dried bunches in single layers in lined cardboard boxes.
Grape fruit can be eaten fresh or in desserts. They can also be used in the production of wine, as raisins, canned grapes and for the production of grape juice. The fruit is rich in calcium, iron, phosphorous, vitamin C, and amino acids. Black and red grapes are rich in natural anti-oxidants.