CASHEW (Anacardium occidentale)

 

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Cashew varieties

 

Planting materials
Cashew can be propagated by seedlings, air layers and softwood grafts. Since it is a cross-pollinated crop, vegetative propagation is recommended to obtain true to type progeny. Field establishment of air layers have been found to be poor. Hence softwood grafts, which give a high rate of establishment and early flowering, are recommended for planting.

1. Propagation by seedlings

Selection of mother trees
Select mother trees having the following characteristics: (1) Good health, vigorous growth and intensive branching habit with panicles having high percentage of hermaphrodite flowers. (2) Trees of 15-25 years of age. (3) Bearing nuts of medium size and weight (5-8 g/nut) with an average yield of 15 kg nuts per annum. (4) Bearing 7-8 nuts per panicle.

Selection of nuts
Select mother trees in February and collect seed nuts in March-April. Select good, mature, medium sized nuts, which sink in water as seeds after drying in sun for two to three days.

Raising seedlings
Raise seedlings in polythene bags during May. Use polythene bags of size 20 cm x 15 cm and fill the bags with garden soil, leaving a gap of 1 to 1.5 cm above. Soak seed nuts in water for 18 to 24 hours to hasten germination. Sow the pre-soaked seed nuts in polythene bags filled with garden soil at a depth of 2-3 cm with the stalk end up. Seeds germinate in seven to ten days.

2. Propagation by air layering
Prepare air layers during February-March, so that they will be ready for planting in June-July. Select 9-12 month old pencil-thick terminal shoots. Remove carefully a strip or ring of bark, 0.6 to 1.2 cm thick by using a sharp knife without injuring the underlying wood. Wind a string around the cut area and cover it with moist moss or wood shavings or sand and saw dust mixture or ordinary potting mixture and wrap round with 150-200 gauge polythene film of size 23 x 15 cm. Secure loose ends of film with jute fibre. When roots emerge from the ringed portion in 40-60 days, give a 'V' cut at lower end of treated shoot. After about 15 days, deepen the cut slightly. Cut and separate rooted shoot about 7 days later. Pot the layers immediately after separation from the tree into containers of size 15 x 15 cm made from coconut husk and keep them in shade. Avoid excessive watering. Plant the layers along with the container in the prepared pits with the onset of southwest monsoon. Provide shade and mulch with dry leaves to reduce sun-scorch in tender plants. It is advisable to defoliate the layers two weeks before separation from the mother plant.

3. Propagation by grafting / budding
Different methods of grafting viz., epicotyl grafting, softwood grafting, veneer grafting, side grafting, patch budding etc. have been tried in cashew with varying degrees of success. Among them, softwood grafting was found to be the best for commercial multiplication of cashew.

Softwood grafting

Selection of seed nuts

(1) Seed nuts may be collected during the peak period of harvest (February-March) and sun-dried for 2-3 days.
(2) Quality seed nuts may be selected by immersing in water or 10% saline solution. Seeds, which sink in water, may be selected. (3) Medium sized nuts (7-9 g) may be selected to get vigorously growing seedlings.

Raising rootstocks

1. Fresh seed nuts are to be used for raising rootstock. Seed nuts stored for more than one year may be avoided.
2. The seed nuts should be soaked in water overnight before sowing.
3. Use polythene bags (size 25 cm x 15 cm, 300 gauge thickness) for filling potting mixture.
4. Punch about 16-20 holes on the polythene bags to ensure good drainage.
5. Prepare the potting mixture (1:1:1 ratio of red soil, river sand and compost) mixed with rock phosphate @ 5 g per 2 kg potting mixture.
6. Fill the polythene bags up to the brim of the bag.
7. Sow the pre-soaked nuts in the centre of the bag with stalk end up, at a depth of 2.0-2.5 cm.8. Water the bags immediately after sowing and daily thereafter. Avoid excess irrigation.
9. Nuts usually germinate within 15-20 days after sowing during monsoon months and within 8-10 days during dry months.
10. Nuts should be sown at weekly intervals to get continuous supply of rootstocks.
11. During summer, provide partial shade to the seedlings till they change their bronze colour to green and then keep them in the open.
12. The seedlings will be ready for grafting in 50-60 days after germination.
13. Prevent damage to germinating nuts from squirrels, birds etc.
14. During the rainy season, damping off of young seedlings is common. To control this disease, spraying/drenching Bordeaux mixture (1%) is effective.

Selection of rootstock
Select 50-60 day old healthy seedlings having single main stem grown in the centre of the polythene bag, as rootstock.

Selection of scions

(1) Select a high yielding variety of cashew as a mother plant to collect adequate number of scions.
(2) Select 3-5 month old non-flowering lateral shoots of current season's growth.
(3) The selected scions should be 10-12 cm long, straight, uniformly round and pencil thick with brown colour having dormant plumpy terminal bud. The top 4-5 leaves should be dark green in colour indicating proper maturity of the scion.

Pre-curing

(1) Pre-cure the selected scions by clipping off three fourth portion of leaf blades.
(2) Scions will be ready for grafting in 7-10 days after leaf removal.

Collection of scions

(1) The pre-cured scions are to be cut early in the morning to avoid desiccation.
(2) The scions should be collected before the terminal buds sprout.
(3) Wrap scions in moist cloth and put in polythene covers as soon as they are cut from the mother tree and bring them to the nursery for grafting. If necessary, they can be stored for 3-4 days and used for grafting.

Preparation of rootstock
(1) Retain two pairs of bottom leaves and remove others from the selected seedlings using a sharp knife.
(2) Give a transverse cut on the main stem, 15 cm above ground level.
(3) A cleft of 4-5 cm deep is made in the middle of the decapitated stem of the seedling by giving a longitudinal cut.

Preparation of scion
(1) Select a matching scion stick (same thickness as that of the rootstock).
(2) The cut end of the scion is shaped to a wedge of 4-5 cm long by chopping the bark and wood from two opposite sides.

Grafting

1. The wedge of the scion is inserted into the cleft of the rootstock, taking care to ensure that the cambium layers of stock and scion are in perfect contact with each other.
2. The graft joint is secured firmly by a polythene tape (1.5 cm wide and 30 cm long).
3. The scion of the graft is to be covered with a wet polythene cap (15 x 12.5 cm, 100 gauge thickness) and tied at the bottom to maintain humidity inside and to protect the apical bud from drying. The polythene cap should not touch the terminal bud.
4. The grafted plants are to be kept under shade for 10-15 days to enable sprouting of the terminal buds.
5. The polythene caps are to be removed and the grafts shifted to open place. The successful grafts show signs of growth within 3-4 weeks after grafting.
6. The grafts will be ready for planting 5-6 months after grafting.
7. The success in softwood grafting is more during the period from March to September under Kerala conditions.

Care in the nursery

1. The grafts are to be watered regularly using a rose can or micro-sprinkler.
2. Remove new sprouts emerging from rootstock at frequent intervals.
3. Panicles, if produced by the grafts, may be removed as and when observed.
4. Shift the grafts frequently from one place to another to prevent them from striking roots into the ground.
5. Frequent spraying of insecticide is required for controlling the infestation of sucking insects.

Graft production under polyhouse

Softwood grafts can be prepared almost throughout the year with a mean graft success of about 60-70%. Higher success is achieved during the monsoon season. For this, low cost polyhouses (prepared from casuarina / bamboo poles / areca reapers / GI pipes / PVC pipes and covered with high density polythene sheet of convenient dimensions, preferably 20 m long and 6 m wide may be utilized for graft production. The height of the polyhouse should be 2.5 m in the middle and 1.0 m on both sides. The plants may be watered using hose. Misting units can also be fitted at appropriate points and switched on for about 5-10 minutes at an interval of two hours from 10 a.m to 6 p.m during summer season. This reduces the temperature build up inside the polyhouse. Raising of rootstock seedlings, grafting of rootstocks and maintenance of grafts can be done inside the polyhouses. These polyhouses give protection to the seedlings and grafts during heavy rains and reduce the mortality. Again during summer months the seedlings / grafts can be maintained in these polyhouses by covering with HDPE shade nets (35-50% shade).

Planting and management of grafts

The softwood grafts will be ready for planting in 5-6 months after grafting. The pits are filled with topsoil and 5-10 kg of compost or dried cowdung / pit and the grafts are planted after carefully removing the polythene bags. Care should be taken while planting to see that the graft union is 2.5 cm above the ground level. The polythene tape is to be carefully cut and removed subsequently. Staking should be done immediately after planting to protect the grafts from damage.

Planting and management of plantation

Plant seedlings, air layers or softwood grafts in pits of size 50 x 50 cm during June-July.

Planting may be done at a spacing of 7.5 m for poor and 10 m for rich and deep soils and sandy coastal area. On very sloppy lands, the rows may be spaced 10-15 m apart with a spacing of 6-8 m between trees in a row.
Initial training / shape pruning

The sprouts coming from the rootstock portion of the graft that is from the portion below the graft joint should be removed frequently during the first year of planting. Initial training and pruning of young cashew plants during the first 3-4 years is essential for providing proper shape. Thereafter, little or no pruning is necessary. The plants should be allowed to grow by maintaining a single stem up to 0.75-1.00 m from ground level. This can be achieved by removing the side shoots or side branches gradually as the plants start growing from the second year of planting. Weak and criss-cross branches can also be removed. Branches growing unwieldy may also be cut off. Proper staking of the plants is required to avoid lodging due to wind during the initial years of planting. Initial training and pruning of cashew plants facilitate easy cultural operations such as terrace making, weeding, fertilizer application, nut collection and plant protection. The flower panicles emerging from the grafts during the first and second year of planting should also be removed (deblossoming) in order to allow the plant to put up good vegetative growth. The plants are allowed to flower and fruit only from the third year onwards.

General pruning

In older cashew plantations, removal of dried or dead wood, criss-cross branches, water shoots etc. should be attended to at least once in 2-3 years. This allows proper growth of the canopy and receipt of adequate sunlight on all the branches. Pruning of cashew plants should be done during May / June.

Intercropping

Pineapple is the most profitable intercrop in cashew plantation in the early stages of growth. It can be planted between two rows of cashew in trenches opened across the slope. Paired row of pineapple suckers can be planted in each trench at 60 cm between rows and 40 cm between two suckers with in the row. These trenches can be opened at 1 m between two rows of cashew. Ginger, lemongrass and tapioca are also suitable as intercrops.

High density planting

High density planting is a recent technique recommended for enhancing the productivity of cashew plantations. This technique involves planting more number of grafts per unit area and thinning at later stages. Instead of the normal planting density of 64 to 177 plants per hectare (spacing ranging from 7.5 to 10 m in the square system of planting) or 74 to 204 plants (spacing ranging from 7.5 to 10 m in the triangular system of planting), 312 to 625 grafts will be planted per hectare, initially. During later years, as the canopy develops, plant population is to be regulated by selective felling to minimize competition.

While adopting a high density planting technique, grafts may be planted initially at a spacing of 4 x 4 or 8 x 4 m so that there will be 625 or 312 plants respectively. This population can be retained for a period of seven to nine or ten years depending upon the canopy expansion rate. If the soil is very rich the canopy development rate will be faster. High density planting would be more useful in poor soils where the rate of canopy expansion is slow. Considering the fertility status of the soil, the level of management in terms of fertilization, irrigation etc. the initial plant population is to be decided carefully for every agro-climatic condition. Later, after monitoring the canopy pressure between adjacent plants, the alternate plants are to be removed. Finally, when the plants attain full growth, the spacing between the plants will be 8 x 8 m.

If uniform management practices are adopted, during early years of yield, the per tree nut yield will be more or less the same with all the trees, in both the conventional system of planting and in high density planting. But the per hectare yield will be more from high-density plantations (due to higher plant populations) compared to the normal density plantations. During later years, when the plant population is equalized to that of normal density plantation, the productivity of both the plantations would be more or less the same. The bonus yield obtained during the early years of yield would be substantial in high-density plantations.

In addition to obtaining higher yields, substantial quantities of firewood can be obtained during thinning, which may fetch additional revenue to the farmer. The weed growth in the interspace can be effectively checked to a greater extent.

Top working

Top working is a technique evolved to rejuvenate unproductive and senile cashew trees. Top working can successfully rejuvenate poor yielders in the age group of 5-20 years. The unproductive trees are to be beheaded at a height of 0.75 to 1.00 m from ground level. The stem should be cut with a saw to avoid stump splitting. The best season for beheading trees is May-September. Soon after beheading, the stumps and cut portions should be given a swabbing with copper oxychloride and carbaryl 50 WP (50 g each per litre of water). Sprouts emerge 30-45 days after beheading. Sprouting will be profuse in young trees. New, 20-25 days old shoots should be grafted with scions of high yielding varieties using softwood grafting technique. To ensure at least six or seven successful grafts, 10-15 grafting are to be done on the new shoots of every tree. The best season for grafting is July-November. Thinning of the extra shoots arising from the stumps should be done to obtain better growth of the grafts. Removal of sprouts below the graft joint and removal of polythene strip from the graft joint should be done. Top working is simple and can be done by farmers after getting proper training.

The top worked trees start yielding right from the second year after top working. Thus precocity can be considered as one of the best advantages of this technique. The major disadvantage associated with top working is the huge casualty of trees due to stem borer attack. Intensive care and management to ward off stem borer is essential. As such, adoption of top working on a larger scale would be difficult.

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 A fertilizer dose of 750 g N, 325 g P₂O₅ and 750 g K₂O per plant is recommended for cashew. Apply 1/5th dose after the completion of first year, 2/5th dose during second year and thus reaching full dose from 5th year onwards. Broadcast the fertilizer within an area of 0.5 to 3.0 m (15 cm deep) around the tree and incorporate by light raking.

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