RUBBER

Harvesting

Tapping and stimulation

Latex is obtained from the bark of the rubber tree by tapping. Tapping is a process of controlled wounding during which thin shavings of bark are removed. The aim of tapping is to cut open the latex vessels in the case of trees tapped for the first time or to remove the coagulum which blocks the cut ends of the latex vessels in the case of trees under regular tapping.

Bark

An inner layer of soft bast, an intermediate layer of hard bast, and an outer protective layer of cork cells can be distinguished in the bark of the rubber tree. The vessels are concentrated in the soft bast arranged in a series of concentric rings of interconnecting vessels.

Marking

Panels are marked on the trees selected for tapping, using a template and marking knife. After deciding the position of the panel, a vertical line, called front channel line, is drawn. On this line, the opening height is marked. Another vertical line, called back channel line, is marked on the half spiral point above the opening height. With the aid of the template placed between these two lines, at the opening height, ensuring a high left to low right, the line for tapping cut and a few guidelines are marked through the grooves. The vertical front end of the template should be kept on the front channel of the tree, parallel to it and the free end of the template is wound on the trunk towards the left side. After marking the guidelines, spout and cup hanger are fixed. Subsequent guidelines are marked every year before commencing of tapping.

Slope and direction of tapping cut

The tapping cut of the budded trees should have a slope of about 30? to the horizontal. For seedling trees, the cuts need to have a slope of only about 25?, since the bark is fairly thick.

The latex vessels in the bark run at an angle of 3-5? to the right and therefore a cut from high left to low right will open greater number of latex vessels.

Latex flow

Hevea latex in the latex vessels of tapped trees contains 30-40 per cent rubber in the form of particles.

The best yield is obtained by tapping to a depth of less than 1 mm close to the cambium.

Tapping implements

The main implements used for tapping and collection of latex are knives, spouts, cup hangers, collection cups, collection buckets and scrap baskets.

Types of tapping knives

• ‘Michie Golledge’ knife
• ‘Jebong’ knife, commonly used in Malaysia, is more suitable for speedy and easier tapping but with a slightly higher bark consumption.
• Modified gouge knife is in use mainly for controlled upward tapping (CUT).

Spout

A metal piece made of galvanized iron (GI) or tin sheet (5 x 3 cm size) bent all along into a V-shape.

Cup hangers

Used to keep the collection cups in place below the spouts. They are made of GI wire and tied on the trees with the help of plastic thread.

Collection cups

Coconut shells are widely used. These are now almost completely replaced by higher capacity (400–900 ml) and cleaner plastic cups.

Scrap baskets

Used for collection of field coagulum or scraps such as tree lace, cup scrap etc.

GI buckets

Commonly used for carrying away the latex from the field.

Time of tapping,/

It is necessary to commence tapping early in the morning, since late tapping will reduce the exudation of latex due to increased transpiration by the trees.

Tapping task

Normal tapping task (The number of trees allotted to a tapper for a day’s tapping) in India varies from 300 to 400 trees.

Tapping Systems

• Budded trees: Half spiral alternate daily (1/2S d/2) system
• Seedlings: Half spiral third daily (1/2S d/3) system
• Medium yielding clones (RRIM 600, GT 1, PB 28/59 etc): Alternate daily tapping
• High yielding clones (RRII 105, PB 217): Low frequency tapping systems (d/3, d/4 & d/6) with stimulation may be practiced

Panel Notation

Panel notation indicates the panel position and renewal succession of the panel. This helps to describe tapping. Common panel notations are B0-1 (A) (First basal panel of virgin bark), B0-2 (B) (Second basal panel of virgin bark), BI-1 (C) (First renewed bark of B0-1), BI-2 (D) (First renewed bark of B0-2), BII-1 (E) (Second renewed bark of B0-1) and BII-2 (F) (Second renewed bark of B0-2).

First, second, third and fourth high panels of the virgin bark above the standard height of opening are indicated by HO-1, HO-2, HO-3 and HO-4 respectively. Renewed bark is usually not tapped in high panels.

Intensive tapping

Intensive tapping is generally done on old rubber trees for a few years prior to their removal.

High level tapping

When tapping of renewed bark on basal panels becomes uneconomic, new cuts are opened at higher levels, 180 cm from bud union or even higher. The tapper uses a small ladder to reach the cut.

Controlled upward tapping

Controlled upward tapping (CUT) can be practiced for longer exploitation of the virgin bark above the basal panel. In CUT, instead of using ladder, a long handled modified gouge knife is used for upward tapping from the ground.

The tapping cut can be 1/4 spiral and its angle 45?. Length of the handle used for tapping is 120 cm for tapping up to 40 cm height of the high panel and 180 cm for tapping beyond that height.

Rainguarding

About 35-40 additional tapping days could be obtained every year by rainguarding the trees by fixing polythene (LDPE) rain-guard to the trunk above the tapping cut. Systematic application of panel protectants at frequent intervals is necessary because chances of bark rot disease are high. Raingurding is recommended only in areas where the yield is 675 kg/ha/annum or more and 25 or more tapping days are annually lost by rain.

Four types of rainguards, viz. polythene skirt, ‘Tapping Shade’, ‘Guardian Rainguard' and ‘Tapping Shield' are recommended and popularized.

Tapping rest

During refoliation and flowering of rubber trees, the yield will be comparatively poor and normally trees are given about four weeks rest if the soil is very dry and yield is uneconomic.

Yield stimulation

Certain chemicals can induce ethylene formation in the plant tissue while certain other groups of chemicals can generate ethylene directly by decomposition. Between the two types of chemicals tested, Ethephon containing 2-chloro-ethyl phosphonic acid as active ingredient, has proved to be a very potent yield stimulant.

Under low frequency tapping systems, trees are stimulated from the first year of tapping using ethephon (2.5%) by panel application method to achieve sustainable yield. Use of ethephon is also recommended for trees tapped under d/2 frequency (panel C) and trees tapped in panel D (BI-2) for short-term increase in production. In newly opened trees or on trees tapping resumed after annual rest, ethephon at 5% (active ingredient) concentration may be applied once (over the lace after two tappings).

The application is done with a brush just above the tapping cut to a width of 1 cm, on the cut surface of the bark over the lace or after removing it. The 10% formulation of ethephon available in the market can be diluted to 2.5 % or 5% with palm oil, petroleum jelly, coconut oil or even with water. The water-mixed formulation should not be kept for more than two hours.

Continuous application of ethephon is not recommended for periods of more than three years at a stretch, under d/2 frequency of tapping.

Puncture tapping

In puncture tapping, an ethephon-based stimulant is applied to a strip of scraped bark, usually vertical, 1.5-2.0 cm wide and 50-100 cm long. On each tapping day, 4-10 punctures are made, at equal spacing in the stimulated bark and latex is collected.

A vertical strip of 50 to 60 cm length with 6 punctures per tapping, stimulation with 2.5 per cent ethephon and a third daily or lower frequency tapping appear suitable for most clones. At monthly intervals, a new strip adjacent to the old strip is prepared, stimulated and puncture tapped. Trees can be puncture tapped when they attain a girth of 40-45 cm, one year before normal opening.

Advantages

1. Low requirement of skilled labour
2. Substantially larger task size
3. Better girth increment
4. Chances of less or no panel dryness
5. Possibility for exploitation at an early age

Disadvantages

1. Spillage of latex (if not properly guided along the strip)
2. Late dripping
3. Need for frequent stimulation
4. Adverse bark reactions like external flaking, bark burst and uneven swellings on the bark

It may be prudent to avoid puncture tapping in sensitive clones like PR 107, PR 251, PR 255 and RRIM 600.

Precautions

1. Puncture should avoid cambium, but should be deep enough
2. Puncture should be distributed uniformly along the stimulated portion
3. Needle should have a diameter of 1 mm with blunt tip
4. Ten applications of Ethephon (2.5 per cent active ingredient) per year will be required

Slaughter tapping

Highly intensive tapping prior to replanting is the last stage in the tapping cycle and is called slaughter tapping. It is done at higher levels, sometimes even on branches, with the help of ladders to extract as much latex as possible from the available bark.

Last updated: 24-05-2008