Cocoa: Weed Control

Effects of weeds on cocoa

There is very little information reported in Malaysia or elsewhere on the effects of weeds on growth or yield of cocoa. Wood (1975) has cited a few references from Ghana and Trinidad where it appears that improved weed control is beneficial to growth and the number of seedlings that needed replacement. Brown and Boeteng (1972) obtained best growth of seedlings with spraying paraquat alone compared to paraquat followed up with dalapon and hand weeding (Table 5).

Table 5 : Effects of weed control on cocoa stem diameter (cm) in Ghana
(Brown and Boateng, (1972)

Treatments

Low slashing

Dalapon/ Paraquat

Circle weeding + high slashing

Paraquat

S.E.

Pre-treatment

0.94

0.94

0.95

0.94

0.02

5 mths. treatment

1.27

1.27

1.33

1.29

0.04

11 mths. treatment

1.33

1.39

1.43

1.59

0.04

17 mths. treatment

1.87

1.93

1.98

2.35

0.08

In Malaysia although there is no trial data, it is obvious from observations that cocoa seedlings grow poorly in weedy conditions and that seedlings in such areas are frequently very uneven in growth.

Weeds probably affect growth of cocoa in the following manner:-

  • Compete for moisture
  • Compete for nutrients
  • Compete for light i.e. shade out the cocoa
  • Climb up and ‘choke’ plants
  • Cause poor access
  • Affect growth of the shade plants in much the same manner as for cocoa and thereby affect the growth of young cocoa seedlings.

In the stages of early growth, moisture stress in particularly critical to the young cocoa seedlings. To reduce the stress, the cocoa plants defoliate their lower leaves. This has a subsequent severe effect on rate of establishment, early growth and initial yields from the loss of photosynthetic capability and nutrient reserves in the leaves.

It is therefore especially important that weed competition is minimal during early growth stages of the cocoa plant. This will enable good even growth which is an essential ingredient for high early yields.

From the third year in a well-established cocoa planting canopy coverage of the ground is significant and the heavy shade from the cocoa has greatly reduced weed growth. However in uneven plantings, usually also accompanied by high light availability, weed growth is still vigorous and competition could be significant still.

Weed problems are usually minimal in the good stands of cocoa from the fifth year when thick canopy coverage and layer of cocoa litter has been built up.

Weed Control programmes

The main aims of the weed control programme should be:-

  • to minimize competition for moisture
  • to minimize competition for nutrients
  • to prevent weeds climbing up and engulfing the plants
  • to allow easier access to the bushes for field operations

As discussed earlier, weed competition is more critical in young cocoa and weed control programmes should reflect this. The weed control programmes may therefore be broken down to the following stages:-

  • Pre-planting
  • Establishment of shade
  • Young immature cocoa in pre-jorquette, say 0-½ year
  • Immature cocoa, say ½-1½ year.
  • Young mature cocoa, say 1½ – 4 years
  • Mature cocoa, say 5 years +

Measures recommended are given in Appendix 1.

APPENDIX 1 Weed Control Programme in Cocoa

Stage

Weed control programme

Under thinned jungle

Mono-cocoa

1. Preplanting 1. Thin out excess shade trees 1. Spray strips for shade trees planting (as necessary)
2. Eradicate perennial weeds 2. Eradicate perennial weeds
3. Eradicate creepers 3. Eradicate creepers
2. Establishment of shade trees 1. Thin out excess shade trees 1. Maintenance of strips or rings of all planted shade trees; say monthly x 9 rounds; thereafter 1½ monthly x 2 rounds
2. Maintenance of strips or rings of all planted shade trees; say monthly x 6 rounds; thereafter maintain present shade trees 1½ monthly x 4 rounds 2. Selective spray/weed perennial weeds and all creepers in interline at 3 monthly intervals
3. Young immaturecocoa 1. Prior to planting cocoa, spray planting strips 1. Prior to planting cocoa, spray planting strips
2. Maintenance of rings around seedlings or planting strips say monthly x 4 round (hand weeding) monthly x 2 rounds (herbicide) 2. Maintenance of rings and seedlings or planting strips say monthly x 6 rounds (hand weeding)
3. Selective weed/spray perennial weeds and nil creepers in interline at 3 monthly intervals 3. Selective weed/spray perennial weeds and nil creepers in interline at 3 monthly intervals
4. Immature cocoa 1. Maintenance of rings around seedlings or planting strips, say monthly x 6 rounds, thereafter say 1½ monthly x 8 rounds (all herbicide sprays) 1. Maintenance of rings around seedlings or planting strips, say monthly x 9 rounds, thereafter say 1½ monthly x 6 rounds (all herbicide sprays)
2. Selective weed/spray perennial weeds and all creepers in inter-line at 4 monthly intervals. Leave low soft grasses. 2. Selective weed/spray perennial weeds and all creepers in inter-line at 4 monthly intervals. Leave low soft grasses.
3. Thin out excess shade trees 3. Thin out excess shade trees
5. Young Mature cocoa 1. Maintenance of rings and bushes or planting strips, say 1½ months x 4 rounds, thereafter say bimonthly x 12 rounds 1. Maintenance of rings and bushes or planting strips, say 1½ months x 4 rounds, thereafter say bimonthly x 12 rounds
2. Extra weeding rounds for maintenance of rings should be arranged for supplied plants etc as required 2. Extra weeding rounds for maintenance of rings should be arranged for supplied plants etc as required
3. Selective weed/spray perennial weeds and all creepers in inter-line at 4 monthly intervals 3. Selective weed/spray perennial weeds and all creepers in inter-line at 4 monthly intervals
4. Thin out excess shade trees 4. Thin out excess shade trees
6. Mature cocoa 1. Maintain rings around bushes and supplies as required 1. Maintain rings around bushes and supplies as required
2. Selective weed/spray perennial rounds and all creepers at 4 monthly intervals. Leave low soft grasses 2. Selective weed/spray perennial rounds and all creepers at 4 monthly intervals. Leave low soft grasses
3. Thin out excess shade trees 3. Thin out excess shade trees

1. Pre-planting stage. No cocoa or shade trees have been planted and the opportunity should be taken, if possible and feasible, to eradicate perennial weeds and all creepers. At this stage, the most effective chemicals against the weeds may be used as no cocoa or shade plants are present. Such opportunities are most applicable in plantings from belukar or regenerated secondary jungle and probably least applicable under thinned jungle.

2. Establishment of shade. In under thinned jungle situations, where there have been no delay after thinning and in planting up of the permanent shade stand, weed problems are usually minimal and confined mainly to thinning out unwanted trees and spot spraying of weeds which have established in the open areas.

However, if as sometimes is the case, there have been delays or hold-ups after thinning or the jungle has been thinned by natural causes including fires, there could be massive regeneration of weeds which need to be controlled for quick and successful establishment of the shade trees to be planted.

When plantings are monoculture cocoa and planted shade are to be established, regular weed control rounds are required. Usually strips along the planting rows are sprayed regularly to minimize competition.

In attempting to achieve high early yields and to minimize shade manipulation, often shade levels are kept minimal in thinned jungle plantings. This predisposes weed growth especially where seed build-up has occurred after delays in planting programmes etc.

In monoculture cocoa where good uniform establishment of shade is essential for successful and even establishment of cocoa, the weeds must be kept under control for the shade trees to grow well. Usually under these conditions, light is not a constraint and weed growth is luxuriant unless controlled. Weed problems may be expected to be more severe in mono-cocoa areas than under thinned jungle.

3. Young immature cocoa areas. At time of planting cocoa, usually shade levels are between 20-40% in well prepared areas and weed seed build-up has been substantial especially in mono-cocoa areas. It is usual to spray out a blanket herbicide spray to suppress the weed growth before cocoa is planted.

Growth of the cocoa seedlings is not as good initially in cleared jungle areas so that allowance for this in the weeding programme should be given.

Regular weeding programmes are essential to obtain good establishment and even growth. Minimal weed competition at immaturity will allow good and even growth of the planting which in turn will shade out the weed more quickly thereby reducing overall weed control effort.

Hand weeding is recommended initially to ensure minimal damage to the seedlings in case of accidental spray drift.

4. Immature cocoa areas. Regular weeding rounds are still required as considerable light is still available to the weeds still. A good stand will reduce weeding problems so that the policy of full stands and supplying dead/vacant points and poorly growing plants has a beneficial effect on weed control.

At this stage only herbicide spraying is preferred for maintaining the rings and strips as there is minimal damage to roots and soil disturbance.

5. Young mature cocoa areas. Weed problems are expected to be much reduced at this stage as shade from the cocoa canopies increase. Particular problems are expected from the more open areas and where cocoa growth has not been good or where poor growth/vacant points exist. As the weeds present are expected to further retard growth if not controlled, a two-pronged effort to attain good weed control and promote growth of the plants through mulching, additional fertilizer and shade etc. is often required.

6. Mature cocoa areas. At this stage, weed control should be minimal and confined to areas between canopies where there is more light. By now all excess shade trees should have been removed.

The weed control programme are therefore based on the following principles:-

  • minimise weed problems before planting of shade trees and cocoa
  • good weed control in establishment phase of shade trees and cocoa by following regular weeding rounds
  • differential weed control techniques depending on growth of cocoa and amount of light expected which affects weed growth
  • allowing low soft grasses to establish where competition with cocoa is minimal so that run-off and erosion is minimised. In mature cocoa especially, they may also be useful in reducing nutrient loss from the fertilizer applications made.

As far as possible, weed control measures should be timed in conjunction with fertilizer applications. Otherwise weeds present may take up nutrients needed by the cocoa and reduce the growth of the latter.

While the above are direct measures taken on the weeds, as inferred from the discussions, ensuring good growth of the cocoa is also an effective means of the cocoa.

Mulching of the bushes with empty waste bunches of oil palm or coconut husk and similar materials is particularly to be encouraged as it promotes growth and reduce weed growth directly. Where possible this should be considered especially in special situations eg. supplies, very open areas, compact soil areas etc.

A guide on palm circle size or strip width to be kept clean for various ages of cocoa plants and shade trees (Gliricidia) is given in Table 6.

Table 6 : Recommended circle or strip sizes for cocoa

Stage if growth

Cocoa

Shade trees

Circle radius (m)

Strip width (m)

Circle radius (m)

Strip width (m)

1. Pre-planting

na

na

na

1.0

2. Establishment of shade cocoa

na

na

0.5

1.0

3. Young immature cocoa

0.5

1.0

na

na

4. Immature cocoa

0.75

1.5

na

na

5. Young mature cocoa

0.75

1.5

na

na

6. Mature cocoa

1.25

2.5

na

na

na = not applicable

Strip spraying is usually preferred when weed growth is thick as access is also improved.

Hand-weeding in cocoa

Weeding by hand with a small light changkol or sickle is recommended only in the first few months after planting when the plants are small and have no brown bark. The weeds should be removed without disturbance or damage to the cocoa roots and soil. To achieve this, there should be minimal scraping of the soil.

Good supervision is very important and care taken that plants are not damaged or even cut especially in thick weed conditions.

Herbicides for weed control in cocoa

In view of the shallow and superficial roots of cocoa, control of weeds by herbicides in cocoa is preferable to hand weeding with changkol or sickle. However, especially when the plants are small, serious damage may be caused by herbicide drift.

Commencement of use of herbicide spraying in cocoa should therefore be when the plants are large enough and with some brown bark and with sufficient leaves not to be significantly damaged by herbicide if some leaf scorch should happen. The sprayers should also be skilled and careful.

Herbicides have different effects on cocoa (Brown and Boeting, 1972; Tan et al. 1972) and many are less safe to use in view of very serious damage which my be caused, in particular, by the translocated herbicides eg. the phenoxyacetic acids (2, 4-D and 2,4,5-T) and the halogenated aliphatic acids (dalapon, TCA) on accidental damage.

The literature eg. Wood (1975) cites several suitable herbicide mixtures for cocoa containing the above translocated herbicides and including ureas (eg. diuron and linuron) and the triazines (eg. atrazine and simazine) which are absorbed through the roots. It appears highly dangerous to use these mixtures in view of the potential damage which could be caused to the cocoa particularly in situations with low level skilled workers and supervision.

Paraquat is now commonly used because it is a contact herbicide and the safest due to its non-effect on brown bark. Its quick scorching action is useful in frequently wet situations. The main defect is that it is not very effective against Paspalum spp. and other established weeds so that frequent follow-up, spray rounds are required. In very open conditions and with frequent rains i.e. areas favourable to weed growth, significant regeneration is seen within 3 to 6 weeks. Frequent spray rounds are therefore required.

MSMA, another common contact herbicide, has been reported to cause leaf symptoms similar to zinc deficiency and avoidance of its use it generally advocated.

Glyphosphate is a highly effective herbicide against grasses and widely used against lallang and for control of persistent grasses in mature cocoa. There is no information on phytotoxicity in young cocoa.

Flauzifop-butyl which is highly effective against Paspalum spp. And reported to be safe in young cocoa is now being evaluated.

The commonly established shade trees eg. Gliricidia are also equally susceptible to the translocated herbicides.

In view of the above and the very limited range of suitably safe herbicides, the following recommendations are made :-

1. Preplanting : In absence of shade trees and cocoa, the most effective herbicides or herbicide mixtures may be used against the weeds present.

2. Establishment of shade trees : Strip or circle spraying of shade trees with Paraquat at 2-3 l/ha (1½ – 2 pts/ac.) rate depending on amount of light. Higher rates should be used in the open.

In inter-rows, the most effective herbicide mixtures may be used to eradicate the weeds and prepare the areas for cocoa planting but take care to avoid spray drift and contact with the shade trees.

As required, brush killers such as Garlon, and the translocated herbicides as 2,4-D amine alone or in mixtures with Paraquat and MSMA are used. Lallang, a common problem, may also be tackled with glyphosphate or dalapon.

3. Cocoa. Strip or circle spraying with Paraquat at 1.5/3 l/ha (1-2 pt/ac) rate chosen again depending on amount of light.

Persistent grasses may be tackled with glyphosphate spray in mature cocoa. Other persistent broad leaf weeds should be eradicated by hand or brushed/wiped with a brush killer such as Garlon where risk of contact with the cocoa is minimal.

The above recommendations commit the estate to frequent spraying rounds in the early stages of establishment but are probably justifiable in view of the limited period when spraying is required and the dangers posed by “something” going wrong.

In view of the frequent introduction of new herbicides, there is often temptation to try them. This is encouraged but managers should check on possible side effects from the suppliers and also not use widescale until certain that no harmful side effects are likely.

Herbicide application techniques

The 18 l knapsack sprayer is still commonly used. Advances in herbicide application techniques have been made and CDA sprayers using very low volumes have been widely tried in Malaysia recently. Also available now is the very low volume sprayer, the CP15 from Cooper-Pegler which has a pressure regulator and can possibly spray down to 20 t/ha, a significant reduction in water requirement.

The CDA sprayers are more efficient in usage of herbicides and particularly suitable for the translocated glyphosphate against lallang and other grasses. Reductions of chemical requirement by 1/2 to 2/3 have been claimed and the technique should be used in lallang blanket and spot spraying situations. The droplets are however more susceptible to drift and use in very exposed young immature cocoa may not be advisable.

As spray drift is to be avoided as far as possible, use of the correct nozzle with the conventional knapsack sprayer will help. Polijet tip nozzles from ICI to be used in conjunction with paraquat are given in Table 7.

Table 7 : ICI polijet nozzles

Polijet tip colour

Brass Nozzle Equiv.

Throughput* m.l./min.

Swath**
meters

Uses

Red

078

2360

2-2.5

Suitable for spraying circles and strips of 2-2.25 meters wide
Blue

062

1630

1.75-2.0

Suitable for spraying strips of 1.75-2.0 meters or circles of 1.75 meters diameter
Green

052

940

1.5-1.75

Suitable for spraying strips of 1.5-1.75 meters, and in nurseries
Yellow

040

680

0.75-1.0

Recommended for spot spraying, nurseries and in delicate spray operations. (Use lower pressure of 10 p.s.i. to reduce drift)

* Throughput at normal spraying pressure of 15 p.s.i.
** Swathe achieveable at nozzle height of 45 – 50 cm

The yellow polijet nozzle appears most suitable for use in young immature and young mature cocoa and spot spraying situations while the green polijet nozzle is probably best for mature cocoa.

Of course, good maintenance and calibration of the sprayers and nozzles is necessary to ensure good results as well as avoid damage by leaking pumps and misdirected sprays from damaged nozzles.

The use of spray shields to minimise danger of accidental drift especially in young cocoa is encouraged.

Proper safety precautions with the equipment and herbicides are advisable in view of the high toxicity of the principal herbicide used i.e. paraquat and all workers and staff involved should be made aware of the dangers of the chemicals used and precautions which are required including proper storage and labeling of herbicides, proper functioning and use of equipment, protective clothing and other gear as necessary, proper handling of the herbicides and washing up immediately after work.

Assessment of results

The weed control measures taken should be assessed for the following :-

  • achievement of objective in terms of kill and area covered
  • standard of spraying or weeding
  • productivity of labour
  • costs of control

Continuous evaluation of results achieved is essential not only because of the need to improve results all the time in good management practice but because spraying, weather and labour input conditions after very considerably and cause different results from expectation. Quick repeat spraying follow-up action may sometimes be required which will result in lower costs and better control of the weeds and growth of the cocoa in the long run.

Discussion

The answers to the possibilities posed at the beginning of the paper therefore are as follows:_

  • there are very few weed research scientists in this country and they are busy working mainly on crops other than cocoa
  • there are still some weed control problems in cocoa, in particular, limited range of safe herbicides to use and frequent repeated spraying required. However the problem is confined mainly to preplanting and the young immature and mature stages of the crop only, say a period of about 3-4 years mainly
  • weed control is very important in young cocoa but probably not critical in most situations in mature cocoa
  • herbicide usage is low in relation to other crops such as oil palm and rubber, taken over the life of a planting.

Conclusion

For good establishment of cocoa, regular weeding of the shade trees and cocoa seedlings planted is required. Competition from weeds is most severe in young immature cocoa but hand weeding for the first 6 to 9 months and monthly spraying with paraquat is adequate to control the weeds, provided perennial and woody weeds are eradicated before planting. After the cocoa canopies have closed over, weed competition is usually minimal. Overshading from shade trees planted should be avoided.

Delays in weed control in young immature cocoa should be avoided as far as possible and regular assessment of results and early remedial action will be highly advantageous to the cocoa plants.

Reference 
Ooi L.H. and Chew P.S. 1985. Some important agronomic and agricultural practices in cocoa  estates. TDMB Plantation Management Seminar, Kuala Trengganu

Note: The full list of references quoted in this article is available from the above paper.

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