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Harvesting
Hevea latex found in the latex vessels contains 30-40 per cent rubber in the form
of particles. Latex is obtained from the bark of the rubber tree by tapping.
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.
It is generally economic to begin tapping when 70 per cent 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 a 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 (1/2 S 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.
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 300
to the horizontal. For seedling trees, the cuts need to have a slope of only about
250, since the bark is fairly thick.
The latex vessels in the bark run at an angle of 3-50 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.Completion
of tapping and latex flow in the early hours (2 to 6 hours) is good for higher yield
it is particularly important during summer and wind prone areas.
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, RR11 400 series clones, PB260, PB 235, 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.
Low frequency tapping
Low frequency tapping(LFT) with high yielding stimulation using ethephon(2-chloro ethyl phosphonic acid)
can be practiced from the first year of tapping to reduce the cost
of tapping and to increase productive life of trees and timber volume.
The LFT sysyems recommended are d3, d4, d7 frequency.
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 combination of Low
Frequency Tapping with CUT from renewed panel stage can increase the
economic life of trees up to 40 to 50 years.In general 30 to 50 percent higher yield
can be obtained for many years under CUT.
The tapping cut can be 1/4 spiral and its angle 450. 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.
Tapping cut in the high panel can be stimulated using 5 per cent ethephon following
lace application method. For third daily (d3) tapping of quarter spiral cut
in the high panel, monthly stimulation is enough for high yielding clones.(like, RR11 105)
and stimulation once in three weeks interval is necessary for medium yielding clones.
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.
Irrespective of the type of the rain guard used, regular panel
washing using fungicide (mancozeb 0.37%) at 10 to 15 days interval
is necessary to prevent incidence of panel diseases.
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
- Low requirement of skilled labour
- Substantially larger task size
-
Better girth increment
- Chances of less or no panel dryness
- Possibility
for exploitation at an early age
Disadvantages
- Spillage of latex (if not properly guided along the strip)
- Late dripping
-
Need for frequent stimulation
- 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
- Puncture should avoid cambium, but should be deep enough
- Puncture should
be distributed uniformly along the stimulated portion
- Needle should have a diameter
of 1 mm with blunt tip
- 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.
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