CROP HUSBANDRY-RUBBER CULTIVATION PRACTICES IN KERALA

RUBBER (Hevea brasiliensis)

Rubber can be grown from sea level up to an altitude of 500 m in areas of well distributed annual rainfall of not less than 200 cm and a warm, humid equatorial climate (21-35ºC). The soils of main rubber tracts in India, confined to a narrow belt on the west of the Western Ghats, running parallel to it for about 400 km, are mostly laterite in nature. Well-drained alluvial and red loam soils are also suitable for rubber cultivation.

Propagation

(i) By clonal seeds collected from approved poly-clonal seed gardens in the country and abroad.
(ii) By budded plants.
(iii) By tissue culture plants.

The clones may be planted as follows:

Category 1
Budded clone of RRII 105 and PB 260 may be planted to cover only 50% of the total area of any estate or small holding.

Category 2
Budded clones of RRIM 600, Gl 1, PB 28/59, PB 217 and RRIM 703. Three or more of these may be planted to cover up to 50% of the total area of any estate or small holding.

Category 3
Budded clones of RRII 5, RRII 203, PR 255, PR 261, PB 235, PB 280, PB 311 Tjir 1, PB 86, GL 1, PR 107, RRIM 605, RRIM 623, RRIM 628, RRIM 701, PB 6/9, PB 5/51, RRII 118, RRII 208 and polyclonal seeds of approved sources may be planted in very small scale not to exceed 15% of the total area in aggregate.

Nursery

Nurseries are maintained for raising seedlings, budded plants and bud wood. Beds are prepared 60-120 cm wide and of convenient length with path ways laid in between to facilitate manuring, watering, weeding etc.

Spacing in the nursery according to the type of planting materials is as follows:

For raising seedling stumps: 23 x 23, 30 x 30 or 34 x 20 cm
For budded stumps: 30 x 30 cm
For stumped buddings: 60 x 60 cm
For bud wood nurseries: 90 x 90 or 60 x 120 cm

Intensive care may be exercised in the nursery than in the field for the rapid production of healthy planting materials by adopting proper mulching, weeding, manuring, pest and disease control measures.

Planting techniques
Rubber plantations in India are mostly situated on sloppy and undulating lands. On such lands and hilly areas, adequate soil conservation measures should invariably be resorted to.

Planting distance
The planting density recommended is 450 to 500 plants per hectare.

Pitting and refilling
The standard pit size recommended is 75 x 75 x 75 cm. Slight variations may be made depending on the nature of the soil. While digging the pit, topsoil should be placed on one side and subsoil on the other side. Filling should be done with topsoil as far as possible. Apply manure thoroughly mixed with the top 20 cm of the soil in the pit.

Type of planting
i. Seed-at-stake planting: Planting seeds in situ is not found very successful in the country.
ii. Stump planting: Seedlings raised in nurseries are transplanted after pruning the stem at a height of 45-60 cm from the collar.
iii. Polybag plants: These plants are raised in two ways.
(a) Raise stock seedlings in polybags and afterwards green bud them at the appropriate stage and transplant.
(b) Green budded stumps are planted in polybags of appropriate size and transplanted.
In both the cases, transplanting can be done when the plants attain either 2-3 whorls or 6-7 whorls of leaves.
iv. Budded stump planting: Seedlings raised in nurseries are budded and transplanted after pruning the stem at about 8 cm from the bud patch.

Cover crop
It is strongly recommended to have ground cover crops particularly of leguminous creepers. The most common cover crop used is Pueraria phaseoloides and Mucuna bracteata. Since the seeds of cover crops often have very hard seed coats, it is advisable to have certain pre-sowing seed treatment such as acid treatment, hot water treatment, and abrasion treatment to obtain a high percentage of germination.

Mulching
This is recommended from early stage of plants using dry leaves, grass cutting, cover crop lopping etc. around the plants. Usually November is the ideal time for mulching to protect the plant from the adverse effect of drought.

Manuring
Manuring of plants is done in three important stages of growth namely nursery, young plants and mature trees.

Seedling nursery
Apply 25 kg of compost and 3.5 kg of rock phosphate per 100 m2 of the nursery bed as basal dressing.

Application of 2500 kg of 10:10:4:1.5 N:P2O5: K2O:MgO mixture per effective hectare (i.e. 25 kg per 100 m2 of the nursery bed), 6-8 weeks after planting is recommended. To make 100 kg of the above mixture, use 48.5 kg ammonium sulphate (20.6% N) or 22 kg urea (46% N), 34.5 kg rock phosphate (29.0% P2O5), 7 kg muriate of potash (60% K2O) and 10 kg commercial magnesium sulphate (16% MgO) or 4 kg magnesite (40% MgO). Use a filler to adjust the total weight of the mixture to 100 kg.

Bud wood multiplication nursery

1. Incorporate 150 kg powdered (100 mesh) rock phosphate per hectare i.e. 1.5 kg per 100 m2 of the nursery bed as a basal dressing at the time of preparing the nursery bed.

2. Apply of 250 g of 10:10:4:1.5 NPKMg mixture, the composition of which is given earlier, per plant in two equal split applications for the first crop of bud wood. The first application should be made 2-3 months after planting the budded stumps or cutting back if budding is carried out in situ. The second application should be made 8-9 months after planting.

3. Apply 125 g of 10:10:4:1.5 NPKMg mixture, per plant in one single application 2-3 months after cutting back for the second and subsequent crops of bud wood from the nursery.

Immature rubber trees
Apply compost / FYM @ 12 kg/pit and rock phosphate 175 g/pit at the time of filling the pit.

From first to fourth year, 10:10:4:1.5 NPKMg mixture may be applied @ 225, 450, 450, 550, 550, 450 and 450 g / plant at the 3rd, 9th, 15th 21st, 27th, 33rd and 39th months, respectively.

From 5th year, till tapping begins, where cover crops were grown and mulching was practiced during the initial years, 12:12:12 N:P2O5:K2O mixture may be applied @ 125 kg/ha during April-May and September-October. To make 100 kg of the above mixture, 26 kg urea, 54 kg rock phosphate and 20 kg muriate of potash are required. Whereas, in plantation without cover crops and where mulching was not practiced during the initial years, 15:10:6 N:P2O5:K2O mixture may be applied @ 200 kg/ha during April-May and Sept-October. Mix 33 kg urea, 50 kg rock phosphate, 10 kg muriate of potash and 7 kg filler to get 100 kg of this mixture.

Mature rubber under tapping
N:P2O5:K2O (10:10:10) mixture @ 300 kg/ ha or 900 g/tree may be applied every year as a single dose during April-May or in two splits during April-May and September-October. To make 100 kg of this mixture, use 22 kg urea, 50 kg rock phosphate, 17 kg muriate of potash and 11 kg filler.

Instead of the above fertilizer mixture, any of the complex fertilizers of the grades 15:15:15 or 17:17:17 or 19:19:19 N:P2O5: K2O may also be used. The quantities of these being 200 kg, 175 kg and 160 kg/ha, respectively. Ammophos (20:20) @ 150 kg mixed with 50 kg of muriate of potash can also be used for one hectare. For mature rubber, it will be desirable to follow discriminatory fertilizer recommendation based on soil and leaf analysis. This facility is available at the Rubber Research Institute of India, Kottayam and also at the Regional Laboratories at Adoor, Kanjirapally, Pala, Muvattupuzha, Thrissur, Kozhikode and Nedumangadu .
Note: Plantations where rubber trees exhibit magnesium deficiency symptoms (interveinal yellowing of leaves during September-October) addition of 50 kg of commercial magnesium sulphate per ha besides the above NPK mixture is recommended.

Weeds and weed control
The weeds commonly found in the rubber plantations are Chromolaena odorata (eupatorium), Pennisetum sp., Lantana aculeata, Mimosa pudica and Imperata cylindrica. Growing ground cover crop is the most efficient practice for weed control in rubber in early stages. In rubber plantations, the weeds can be controlled either by manual or chemical means.

The following weedicides are used in rubber plantations:

Pre-emergent: Diuron, Simazine, Cotoran, Lasso
Post-emergent: Paraquat, 2,4-D, Glyphosate

Most of the weedicides have adverse effect on growth of cover crops. Hence it may be used only on the platforms (planting lines).

Harvest
Hevea latex found in the latex vessels contains 30-40% rubber in the form of particles. Latex is obtained from the bark of the rubber tree by tapping

Tapping
It is generally economic to begin tapping when 70% of the trees in the selected area attain the standard girth of 50 cm at a height of 125 cm from the bud union for budded trees. For seedling trees, 55 cm at height of 50 cm for BO1 panel and at 100 cm for subsequent panels is the standard.

Time and interval of tapping
The best month to open new areas for tapping is March. It is necessary to commence tapping early in the morning as late tapping reduces the exudation of latex. In general, budded trees are tapped on half spiral alternate daily (1/2S d/2) and seedling plants on half spiral third daily (1/2S d/3). In the case of high yielding clones like RRII 105, third daily tapping frequency (1/2S d/3) has to be followed to reduce the incidence of tapping panel dryness.

Plant protection

Abnormal leaf fall (Phytophthora meadii)

Symptoms
During southwest monsoon period, the fruits rot. Later, infected leaves fall in large number prematurely either green or after turning coppery red with a drop of latex often coagulated in the centre of a black lesion on the petiole.

Control
Prophylactic spraying of the foliage prior to the onset of southwest monsoon with 1% Bordeaux mixture (3000-4000 l/ha) or oil based copper oxychloride (30-40 litres of CDC-oil mixture / ha mixed in 1:5 proportion) is recommended.

Powdery mildew (Oidium heveae)

Symptoms
Prominently noticed on newly formed tender flush during the defoliation period of January-March. Tender leaves with ashy coating curl, crinkle, edges roll inwards and fall off leaving the petioles attached to the twigs giving a broom stick appearance. In later stages on older leaves white patches appear. Infected flowers and fruits shed.

Control
For young plants, spray wettable sulphur (0.2%) or carbendazim (0.05%) at fortnightly intervals. For mature trees, dust with sulphur 3-5 rounds at weekly to fortnightly intervals. Sulphur mixed with an inert material like talc (70:30 mixture) is generally used @ 11-13 kg/ha/round.

Corynespora leaf disease (Corynespora cassiicola)

Symptom
The disease is prevalent in nurseries (Nov-May) and mature plantations (Jan-May). Large spots with brown margin and pale centre are formed, which later fall off forming shot holes. On mature trees, light green leaves during refoliation are more susceptible. Defoliation and dieback of twigs are also noticed.

Control
Shading in nursery reduces incidence. Spraying mancozeb (0.2%) or carbendazim (0.05%) or Bordeaux mixture 1% is recommended. In mature rubber, micronized spraying with oil-dispersible copper oxy chloride dispersed in spray oil (1:5 proportion) at light green stage of leaves is effective.

Pink disease (Corticium salmonicolor)

Symptom
Trees in the age group 3-12 years are highly susceptible. The seat of infection is usually at the fork region. White or pink coloured cobweb mycelial growths form on the surface of the bark with streaks of latex oozing out from the lesion; resulting in rotting, drying up and cracking up of the affected bark. The distal portions of affected branches dry and dried leaves remain on these branches.

Control
In high disease prone areas, the highly susceptible clones can be treated as a prophylactic measure with Bordeaux mixture or Bordeaux paste. In the early stages of infection, apply Bordeaux paste up to 30 cm above and below the affected region. Tridemorph (2%) incorporated in 1% ammoniated field latex is also effective. Tridemorph (1%) or Thiram (0.75%) in pidivyl, china clay and water mixed in the proportion 1:2:4 by volume is very effective for control. Thiram (0.75%) mixed in petroleum wound-dressing compounds like rubberkote, sopkote, etc. is also effective.

Regular inspection of trees during July to September for detecting the infection is recommended. In severe cases, prune off and burn the dried up branches.

Bark rot (Phytophthora spp.)

Symptoms
During rainy season, when trees are tapped, depressions are formed in the tapping panel due to localized rotting and drying bark. Black vertical lines running downward into the tapping bark and upwards into the renewed bark are noticed. The bark when renewed becomes highly uneven.

Control
The tapping cut and nearby bark should be washed with mancozeb (0.375%) or phosphorous acid (0.08%) at weekly intervals. The rotten bark may be scraped off and applied with fungicide and then covered with petroleum wound-dressing compound.
Other diseases are patch canker, dry rot, Colletotrichum leaf disease, bird's eyespot, shoot rot, brown root etc.

Pests
The pests associated with rubber are scale insect, mealy bug, termite, cockchafer grub, mite, snail, rat, etc. Appropriate control measures may be adopted after identifying the pest.