Coconut: Trial

KCa FERTILISER TRIAL ON COCONUTS INTERCROPPED WITH COCOA IN SEDU SERIES

In 1972, it was noted that `premature’ nut fall incidence was as high as 12 per cent of the nut yield in a Sedu series area. The problem appeared directly due to snapping of the bunch stalk and leaf analysis. Results of groups of palms with and without broken bunch stalks were checked (Table 11).

TABLE 11. LEAF 14 NALAYSIS RESULTS OF COCONUT PALMS WITH AND WITHOUT BROKEN BUNCH STALKS IN ACID SULPHATE AREAS (JULY 1972)

As no clear pattern emerged from the results, it was decided to check the effects of liming and potassium application in the area.

A 2 2 KCa factorial trial was laid down in 1973 on the most affected `premature’ nut fall area with the following results on soil pH, growth, and yields of the underplanted cocoa (1971 planting) and coconuts (1955 planting at 270 palms/ha). The limestone and Muriate of potash were broadcast over a 2 m radius circle around the coconut palms.

Soil pH in the applied area was raised markedly up to 45 cm depth (Table 12).

Liming treatment appeared to depress the number of fronds per palm but had little effect on the frond sizes (Table 13).

TABLE 13. CANOPY MEASUREMENTS OF COCONUT PALMS (1977)

Liming the coconut palms improved copra yields by 10.6 per cent in the hybrid palms and 5.6 per cent in the dwarf palms, primarily by improving copra content per nut. Application of potash at 2.5 kg muriate of potash per palm per year appeared to depress nut yield but increased copra content per unit with subsequent small effect on yields. After 1972 `premature’ nut fall incidence declined markedly to less than three nuts per palm for all treatments (Table 14).

TABLE 14. YIELD OF COCONUTS IN KCa MANURING TRIAL (1973-1977)

Leaf analysis results are in Table 15 .

Liming depressed leaf K and Mg but markedly increased Ca content in the coconut leaves.

Liming had very pronounced effect on growth and yield of the cocoa (Table 16).

TABLE 16. UNDERPLANTED COCOA RESULTS IN KCa TRIAL ON COCONUTS ON SEDU SERIES SOIL

Girth was improved by 10.7 per cent and yield by 70.6 per cent by application of limestone to the coconuts.

Leaf analysis results in the cocoa in 1976 are shown in Table 17.

TABLE 17. LEAF ANALYSIS RESULTS OF UNDERPLANTED COCOA IN KCa TRIAL ON OCONUTS ON SEDU SERIES

Limestone application markedly depressed leaf K levels and increased Ca and Mg levels.

Reference 
Chew P.S., Kee K.K. and Ooi L.H. 1984. Management of coconuts and cocoa on acid sulphate soils. The Planter. Incorporated Society of Planters, Kuala Lumpur 60 (704) : 483-498.

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

Coconut: Planting

COMMERCIAL COCONUTS AND COCOA PLANTINGS ON ACID SULPHATE SOILS

Young Coconuts

There are no young MAWA coconut areas in our group on acid sulphate soils. However, 133 ha of MAWA hybrids were replanted in Estate 1 following rubber in 1980 and 1981 on Briah/Java/Sedu series soils. At the commencement of field preparation, the detailed soil maps were not yet available and following soil pH tests which showed values below pH 3.6 and 4.1 in the top 15 cm, the areas were treated as potentially acid sulphate and field preparations made accordingly. A brief description of the planting practices adopted is given:-

•  Land preparation and drainage. The old rubber was poisoned, felled and burnt. These precautions were taken to minimise rhinoceros beetle problems.

The cleared land was ploughed and harrowed for weed control, to fit new uniform drainage schemes and to level the areas. The practice is useful for mechanization in future and also to benefit the legume growth by reducing initial weed competition.

New drains were then dug at the specifications decided, usually 1 m (width) x 1 m (depth) x 0.5 m (bottom width) at every fourth palm row.

The management was encouraged to practise water management by keeping the water table at 75 cm depth where possible by using weirs in the drains.

•  Planting practices. Standard polybag nursery practices i.e. using 45 cm x 50 cm size polybags, fertilizer schedule (Appendix 2) and daily watering were adopted with satisfactory growth. Top soil was used to fill the bags.

APPENDIX 2. FERTILISER SCHEDULE FOR MAWA COCONUTS IN POLYBAG NURSERY

Leguminous covers were planted in these areas. Again, standard techniques were used although in the acid sulphate areas, liming at 2.5 to 5.0 tons per ha was suggested with apparently beneficial effects to the legumes. Difficulty in establishing and maintaining the legumes in these areas was experienced due to abnormal flooding and probably high acidity. Results obtained usually were legume/grass mixtures.

Normal ring weeding of the palms was carried out to minimise weed competition with the palms.

•  Fertiliser application. The fertilizer schedules followed in the acid sulphate areas are given in Appendix 3.

APPENDIX 3. SUGGESTED FERTILISER SCHEDULES (KG/PALM) FOR HIGH YIELDING HYBRID COCONUTS ON ACID SULPHATE SOILS (CHEW, 1982)

The high rates are to ensure good early establishment and precocious yields for which the MAWAs are famous.

The early growth of the planted MAWAs appeared satisfactory. Only problems were damage by rhinoceros beetles.

Old Coconuts

The policy in all coconut areas is to intercrop with cocoa to maximize profits. Most of the coconut areas on the acid sulphate soils are (>25 yrs) and were planted with a mixture of dwarfs, natural hybrids in 1954/55, at close density for dwarf palms (approx. 6.7 m). Planting practices in these areas are discussed and compared with similar coconut palms planted on non-acid sulphate soils (Sabrang and Briah series) in Estate 2 probably from the same seed palms as Estate 1 and dwarf palms on comparable age in another non-acid sulphate soil (Bernam/Selangor series) in Estate 3.

•  Planting practices. All areas are inter-cropped with cocoa. As this was carried out over a period of years from 1968 and with some considerable conflicting views, planting density and spacings of the cocoa varied considerably but were usually very dense at 750 to 1100 bushes per ha initially and recently thinned down to 530 to 750 bushes per ha.

The ground cover is usually bare of vegetation in view of the dense shade of the cocoa and coconuts and also the deliberate policy of the management to keep out all ground vegetation.

Coconut husks, after removing the nut, which used to be burnt in pre-cocoa planting days are now usually left scattered in heaps in the interrows.

•  Water management. This is stressed in the acid sulphate areas in view of the need for adequate drainage with cocoa planted in the areas and also the potential dangers of higher acidity developing in the soil on over-drainage. Water tables in the acid sulphate areas fluctuated from 0.3 m to 1.2 m but were mostly 0.6 m to 0.9 m.

Often however, with the seasonal rainfall of the estates, excessive water or absence of it was the problem and largely outwith the control of the management.

•  Nutrition. The coconuts were fertilized sparingly as seen in Table 3.

TABLE 3. NUTRIENTS (KG/PALM) APPLIED TO COMMERCIAL COCONUT AREAS (1974 TO 1982)

Fertiliser rates are drawn up on available general information of the nutrient requirements of the palms, leaf and soil analysis results and the fertilizer application made to the cocoa, nutrient requirements of the latter and expected profitability of fertilizer applications made.

Only magnesium applications as magnesium limestone and calcium limestone application were applied at high rates in the acid sulphate areas.

The other feature in the fertilizers applied is the higher nitrogen and potassium application on the Bernam/Selangor series areas. This is in view of the expected responses to nitrogen and the lower leaf K levels.

Applications were withdrawn in the last two years on very low copra prices.

Leaf and soil analysis data on the acid sulphate areas are given in Table 4 and 5 and compared to non-acid sulphate areas.

The soil analysis results given for individual fields in the coconut areas discussed are for fertilized areas in the cocoa interrow areas and mainly unfertilized areas (except for limestone) between the coconut palms.

Soil pH results (air-dry soil) of topsoil samples after 1980 are above four units in all cases. Earlier analysis showed lower pH in the acid sulphate areas but these were subsequently corrected by liming.

Organic carbon, nitrogen and phosphorus contents are higher on the Sedu series than on Bernam series but have lower base cations. Limited analysis results are available for the Sabrang and Briah series areas. Their soil nutrient contents for available P and the exchangeable cations appear similar to the Bernam series.

Nutrients applied to the cocoa are shown in Table 6.

TABLE 6. NUTRIENTS (KG/BUSH) APPLIED TO COCOA AREAS (1976-1982)

High limestone applications were again made in the acid sulphate areas. Applications of nitrogen and phosphorus were lower than on the other soils with approximately similar potassium values.

Leaf analysis results of the cocoa are given in Table 7.

TABLE 7. LEAF ANALYSIS RESULTS OF SOME COMMERCIAL COCOA AREAS ON COASTAL CLAY SOILS

The feature of the results may be higher N and Ca values in the acid sulphate areas.

•  Yields of the coconuts. The coconut yield results in the areas discussed are shown in Table 8 with individual year yield trends in Figure 1.

TABLE 8. COMPARISON OF COCONUT YIELDS (1970-1982) ON ACID SULPHATE AND OTHER COASTAL CLAY SOIL AREAS

In the Malayan dwarf/hybrid areas, there is a gradation of yield increase from the acid sulphate areas to the non-acid sulphate Sabrang and Briah series areas. Yield over the period considered (approximately year 16 to 28) was 38 per cent higher in the non-acid sulphate area. This would be larger probably but for the thinning carried out in 1978 which reduced differences considerably.

The mean yields in the Malayan Dwarf area on the Bernam/Selangor series area appeared comparable to the acid sulphate areas only. However, this may be misleading as unusually poor results (possibly related to abnormally very high rainfall on the estate) were obtained in the last four years despite no thinning carried out.

Copra content figures do not appear to show differences between the different soil areas. However, again this may be misleading due to differences between the years and possibly estate recording methods (Table 9). Copra content is probably better in non-acid sulphate areas.

•  Yields of the cocoa. The cocoa were under planted in the coconut areas in several blocks in each coconut field in the acid sulphate areas due to uncertainty of policy and success over 1968-1975. In the other estates, underplanting of cocoa was carried out in 1968 (Bernam/Selangor area) and in 1969/71 in the Sabrang and Briah soil areas. Planting materials were mainly F1 hybrids.

Yields for some of the oldest plantings have been extracted and yield trends with age for these plantings on the different soils are indicated inFigure 2.

In view of the different planting practices and times, yields up to year five are probably not useful for strict comparison although they indicate that early yield results are also related to acidity of the areas. Yields after year five are shown in Table 10.

TABLE 10. YIELDS FROM COMMERCIAL MATURE COCOA (YR. 6 TO YR. 12) UNDER DWARF/HYBRID COCONUTS ON COASTAL CLAY SOILS

The highest yields were obtained on the Sabrang and Briah series areas under Dwarf/hybrid coconuts. This area outyielded the acid sulphate areas by 59 per cent and 100 per cent. The less acid sulphate areas outyielded the acid sulphate area by 26 per cent. The cocoa in the Bernam/Selangor series outyielded the acid sulphate areas by 44 per cent and 82 per cent.

Absolute yield levels were very low under the generally heavy shade conditions in the acid sulphate areas and even in the non-acid sulphate areas. Improved yield responses seen in Figure 2 in the Sabrang and Briah series area is in part due to reduced shade levels from palm thinning carried out in 1978.

Reference 
Chew P.S., Kee K.K. and Ooi L.H. 1984. Management of coconuts and cocoa on acid sulphate soils. The Planter. Incorporated Society of Planters, Kuala Lumpur 60 (704) : 483-498.

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

Coconut: Acid Sulphate Soils

The acid sulphate soils which are in the coconut areas in our Group of estates were mapped according to the soil identification key drawn up by Paramanathan (1981) and subsequently modified as per Table 1.

Out of 2174 ha of coconuts (mostly underplanted with cocoa), only 338 ha (15 per cent) are on acid sulphate soils of the Sedu and Java Series.

The coconut areas on acid sulphate soils are located in the Bagan Serai (Estate 1) district, and as discussed later, the problem is compounded by difficulties in water management and the markedly seasonal rainfall pattern.

A comparison of the coconuts and cocoa grown on acid sulphate soils in this estate and comparable areas on two other estates on Sabrang and Briah series (Estate 2 in Kuala Kurau district) and on Bernam/Selangor series (Estate 3 in Sabak Bernam district) is given in this paper.

Rainfall patterns for the estates are shown in Appendix 1.

APPENDIX 1. RAINFALL PATTERNS (1971 – 1982) IN COCONUT ESTATES

Reference 
Chew P.S., Kee K.K. and Ooi L.H. 1984. Management of coconuts and cocoa on acid sulphate soils. The Planter. Incorporated Society of Planters, Kuala Lumpur 60 (704) : 483-498.

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

Coconut: Introduction

The yield performances of underplanted cocoa and mixture of dwarf and hybrid coconuts in fields on acid sulphate and non-acid sulphate areas in three coastal estates were compared. The cocoa yields under the heavy shade of coconuts were about 365 to 465 kg per ha per year in the acid sulphate areas against 732 kg per ha per year in comparable non-acid sulphate areas. Coconut yields were 1762 to 2095 kg copra per ha per year against 2439 kg copra per ha per year respectively. Liming from pH 3.9 to pH 4.5 in the topsoil increased copra content per nut and copra yields by 10 per cent and nearly doubled cocoa yields.

Management practices including fertilizer applications, leaf and soil analytical data and water management practices are also described and discussed.

In Peninsular Malaysia, the main areas of established coconut and intercropped cocoa plantations are on the coastal clay soils in the Bagan Datoh, Sabak Bernam/Kuala Selangor and Krian districts. Extensive areas of acid sulphate soils occur amongst the coconut areas. Frequently the presence of acid sulphate soils was not realized until very much later after the coconuts had been planted and when difficulty was experienced in obtaining good results from the under-planted cocoa.

Traditionally, little upkeep and maintenance was carried out in the old coconut areas. Poor performance and yields from the coconuts were often put down to old age of the coconuts and low yield potential of the planting materials. Expectations were therefore low. Information on effects of cultivation practices and management was minimal. With the revived interest in coconuts following cocoa intercropping in the 1960s and the introduction of high yielding MAWA hybrids in the 1970s, more information on coconut cultivation and management has been gathered. However, the research work carried out has been adhoc largely in view of the limited areas of coconuts and cocoa available to support the research programme and other priorities. The problems of cultivating coconuts and cocoa planted in acid sulphate soil areas have not been researched intensively until recently (Zahari et al . 1982). Information on the subject is still lacking. This paper where data from some commercial coconut and cocoa areas on a range of acid sulphate and coastal clay soils are presented may therefore serve as a stop gap measure as further research on the subject is pursued and new information becomes available.

In the group of coconut estates which we were concerned with, updated detailed soil mapping had recently been completed and in this paper, we shall present and discuss our experiences, practices, yield performance and other aspects of management of the coconuts and cocoa which were noted in the acid sulphate areas. A manuring trial was also sited on these soils and the results obtained are also discussed to formulate recommendations for improved performance of the two crops.

Reference 
Chew P.S., Kee K.K. and Ooi L.H. 1984. Management of coconuts and cocoa on acid sulphate soils. The Planter. Incorporated Society of Planters, Kuala Lumpur 60 (704) : 483-498.

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

Cocoa: Pests and Diseases

Cocoa is very susceptible to pests and diseases right from the moment the seeds are sown.

All the plant parts including the pods are affected by various pests (Conway, 1971; Pang & Syed, 1971; Shah, 1976 and Mainstone, 1978) and diseases (Liu & Liew, 1975; Turner & Shepherd, 1978 and Varghese, 1985). Some of them eg. rodents, pod borer, Helopeltis and Phytophthora are capable of causing very high crop losses while VSD has destroyed many young plantings, debilitated mature cocoa bushes and reduced yield in Sabah recently.

Currently the most important pest disease in Malaysia are the moth pod borer, Conopomorpha cramerella and Vascular Streak Dieback (VSD) caused by a fungus Oncobasidium theobromae . The former is confined to Sabah and Sarawak. VSD is present throughout Malaysia.

Conopomorpha cramerella (cocoa pod borer)

The cocoa pod borer was first reported in Sabah in late 1980. The pest if left to build up is capable of destroying the entire crop. Several control measures have been tried to contain the pest including rampassen (i.e. total removal of all pods susceptible to attack) with varying degree of success (Wood, 1980; Day, 1983; and Mumford, 1984).

Currently, no single control measure is entirely satisfactory on its own. A combination of control measures (integrated control) including cultural, biological and chemical methods usually produces better results.

The most common control methods currently practised are:-

• clean and frequent harvesting and breaking of pods as soon as possible and destroying/bagging/burying of husks to prevent pupation.
• selective spraying of moth resting sites i.e. on the undersides of the branches inclined at less than 45^ofrom the horizontal and
• sleeving of young pods to prevent the moths from laying eggs.

Mass rearing of parasitic wasps, Trichogrammatoidea bactrae fumata Nagaraja for release against pod borer eggs and the use of synthetic pheromone for trapping male moths and to disrupt mating are reported to be promising and are still being evaluated. Lately, the Commonwealth Institute of Biological Control (CIBC) in collaboration with EMPA/MCGC have also started a search for exotic natural enemies.

Oncobasidium theobromae (VSD)

The disease causes dieback of canopy and can kill the young bushes. The problem is more serious during the establishment phase. Mature cocoa can usually survive the attack, but varying degrees of yield losses may be expected depending on the severity of the disease and the susceptibility of the cocoa.

Vascular Streak Dieback (VSD) is present throughout Malaysia. Lately, the disease became very serious in Sabah, destroying numerous nurseries and young plantings. Even the mature cocoa bushes were debilitated resulting in vast crop losses.

Byrne (1976) reported 25 to 40% losses in PNG. Taylor and Chong (1983) reported 30% losses when the VSD infested bushes were severely pruned in Lower Perak.

Numerous control measures including pruning, shade adjustment, manuring, fungicide spraying and isolation of nursery and new plantings have been tried. However, the disease was so virulent in 1984/85 that widespread planting failures and high crop losses were reported despite desperate attempts made to control the disease with all the control measures known. It is hoped that 1984/85 were exceptional years in Sabah and that the disease would not be as virulent in the “drier years” when the environment is not as conducive for VSD.

1) Chemical control

A wide range of fungicides have been evaluated in Malaysia and PNG. While none of the fungicide trials carried out in PNG showed any promise, Chung (1983) reported that Bitertanol (Baycor 25% wp) at 0.05% a.i. + 0.05% Agridex sprayed to slight run-off at 14 days interval gave complete protection to nursery seedlings.

Bitertanol is reported to be a protectant and has no curative properties.

Musa & Tay (1984) reported that Benomyl (Benlate), Pyracarbolid and Triforine totally inhibited the growth of VSD mycelium in vitro (lab test). Benomyl applied as soil drench was translocated to the leaves with a residual effect of 1 month. However the efficacy of the fungicides has not been evaluated in the field and therefore cannot be recommended on the basis of actual field trial results.

It must be pointed out here that Benomyl has been reported to be not effective against VSD in the field. Chung (1983) reported that Benomyl did not provide any control at all. Instead the VSD incidence of the Benomyl treated seedlings was higher than the control. More field trials on Benomyl are needed.

Varghese (1985) reported that Triadimenl, Paropiconazole and PP969 are promising in invitro screening.

Currently, Bitertanol appears to be the only fungicide proven to be effective against VSD, although there were some conflicting reports from Sabah. Its application is mainly restricted to the nursery at present. As it has no curative effect, the chemical must be applied in the first instance as soon as the seed starts to emerge followed by a second spray when the first leave emerges and the application continued regularly for as long as the protection is needed.

2) Isolation/Barrier

Under normal conditions, VSD fungal spores do not travel for more than 200 m. An isolation belt of more than 200 m would normally reduce the inoculum potential sufficiently to reduce the chances of infection.

Isolation is most useful for nursery. Isolated nurseries generally have less VSD problem.

In very high inoculum areas, covering the nurseries with ultra-violet light resistant polythene sheets has been reported to confer protection in PNG. The main effect is to keep the leaves dry and hence not conducive to fungal spore germination.

3) Disease avoidance

Avoid planting cocoa during maximum risk period i.e. when the weather is unusually wet for a prolonged period and when the inoculum potential is very high.

Presently, there is insufficient information to define high risk periods accurately. However the following factors taken together may be considered to constitute a high period:-

• in very wet years when rainfall is more than 2000 mm per year.
• When there is continuous wet weather for 4 or more days.
• When very high incidence of VSD is noted and hence high disease pressure.

4) Pruning

Pruning to control VSD is a much debated and controversial subject in Malaysia and deserves a special mention here. The subject has been dealt by numerous authors (Kean & Turner, 1971; Jayawardena et al. 1978; prior, 1980 and Taylor & Chong, 1983).

In Papua New Guinea, it was reported that pruning to remove all VSD tissues and 20 cm beyong the streaking at 2-3 weeks intervals to keep the disease inoculum low is able to control the disease in young cocoa i.e. before the canopy closes over (Odonohue, Pers Comm.)

However, others noted that if pruning is too severe, it could cause more harm and wondered if it is better to leave the bushes alone to allow them to grow out of the disease. The trouble is, not all of them can. At the same time the diseased bushes provide a constant source of inoculum which could result in alarming outbreaks in conducive environments. To derive the best results from pruning, the disease must be controlled in its early stages when it is possible to keep the inoculum at a very low level through regular and frequent prunings.

5) Disease resistance/tolerance

Selection for disease resistance/tolerance is probably the best long term solution for VSD control.

The cocoa industry in PNG was nearly destroyed by VSD at one time. However, with the introduction of VSD resistant/tolerant clones, VSD is now no longer a problem in PNG. Tan (1983) reported that the resistance is polygenic and is not likely to break down easily.

6) Rehabilitation

Varying degree of success have been reported by budding VSD infested bushes with VSD tolerant clones, mainly in Lower Perak.

The approach appears promising.

7) Cultural practice/nutrition

Good cultural practices and nutrition can go a long way to help the bushes to combat the disease. Healthy and vigorous bushes are certainly in a better position to withstand the disease infection and if infected will have a greater chance of recovery.

Manipulation of shade to ensure good aeration and reduction of humidity can also reduce the chances of infection. However, it is important that young cocoa should not be over exposed by excessive shade removal.

Helopeltis, rodents and black pod

Apart from VSD and pod borer, Helopeltis spp (Theivora and theobromae) and rodent pests (mainly rats and squirrels) are also capable of causing very high crop losses in excess of 90%. (Tan, 1974; Mainstone, 1978 and Han, 1982).

The main rodent pests in Malaysia are rats and squirrels. Han and Subash (1980) found that both the rats and squirrels consumed 2.5 to 3.0 pods per feeding in a cage trial. This works up to about 30 to 36 kg of dry bean per rodent per year assuming one feeding per day. The same authors estimated the population of rats and squirrels in an estate in Bagan Serai could reach as high as 100 to 300 and 30 to 90 per hectare respectively. It is therefore not surprising to find the entire cocoa crop lost to the rodents.

The most effective way to control rats in cocoa plantation is baiting with anti-coagulant poison (Friend, 1971; Ooi, 1977 and Han 1982)

Squirrels may be controlled by a combination of trapping with ordinary drop-door rat traps using jack fruit baits (Artocarpus heterophyllus) and shooting. A combination of baiting for rats and trapping/shooting for squirrels is able to reduce the pod damage by rodents to less than 5%. (Wanless, Pers. Comm.)

As Helopeltis initial outbreaks are usually in localized patches, the pest is best controlled at this stage with 2 consecutive sprays of insecticides such as Gama BHC or Propoxur at 10-14 days intervals. To achieve the best results, the pest must be monitored and detected by an Early Warning System and sprayed selectively to prevent major outbreaks (Wills, 1984)

Phytophthora black pod disease is a potentially very serious disease in Malaysia. Shepherd et al. (1977) reported that up to 5% of the crop could be lost to the disease in Lower Perak. The losses are probably higher in the wetter areas such as in Jerangau and certain areas in Sabah. Elsewhere in the world, crop loses of as high as 75% have been quoted by Gregory (1974).

A combination of cultural practices aim at reducing the inoculum pressure through frequent harvesting and proper disposal of diseased pods, pruning to improve aeration and finally chemical control when the infections have reached beyong 5-10% if advocated by Varghese (1985).

McGregor (1982) reported that metalaxyl and cuprous oxide were effective in controlling the black pod disease in Papua New Guinea.

Minor pests/diseases

The other common but less serious pest and diseases recorded in Malaysia include the following:-

1. Colletotrichum leaf spot and phytophthora blight in the nursery
2. Civets, monkey, Dichrocrocis punctiferalis , Porthesia similis and Conopia spp . pod pests.
3. Botryodiplodia theobromae brown pod disease.
4. Zuezera coffeae , Endoclita hosei , Xyleborus spp and Inderbella biciblaga stem/bark borers.
5. Phytophthora stem canker, pink disease (Corticium salmonicolor) and Marasmius thread blight diseases on the stem.
6. A wide range of Coleopteran, Lepidopteran and Orthopteran leaf eating pests
7. White root (Rigidoporus lignosus) and brown root (Phellinus noxius) diseases

From the foregoing, it is not difficult to see that pest and disease control is a very important aspect of cocoa estate management.

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.

Cocoa: Fertilizer Requirements

Introduction

In modern cocoa cultivation, the aim is to maximize early growth and obtain high early yields and sustained peak yields subsequently. To achieve this, it is necessary to have a good understanding of the factors affecting growth and yield of cocoa and to put in the necessary management practices on time as required by the cocoa plant. An essential ingredient in most cocoa growing situations is high fertilizer input. However, the agronomy of cocoa is much more complex than with other crops eg. oil palm and there is very strong interaction between nutrition and other agronomic factors in cocoa such as shade, planting density, pests and diseases etc. To achieve high yields therefore, these factors should not be limiting.

In this paper, the technique for drawing up fertilizer recommendations for the crop is outlined and the interrelationship of the agronomic factors in cocoa plantations with nutrition is discussed. It is hoped that this will enable managers to understand the need for ensuring that planting practices are correct in order to obtain the maximum yield responses from fertilizer applications made.

Nutrient requirement of cocoa

The cocoa plant in its native habitat on the ground storey of the Amazon jungle is very heavily shaded and grows slowly with very low yields. Under these circumstances, nutrient requirements are probably very low.

Nutrients are taken up by cocoa in growth and for yield. The nutrients may be immobilized in the plant or recycled as leaf litter when the plant are mature and the nutrients are exported in the pods that are removed from the field.

The growth and yield potential of cocoa is primarily determined by management factors, soil, climate and the availability of nutrients for growth and yield. The former factors determine the potentials largely and to assess nutrient requirements accurately, a good assessment of the potential growth and yield under the prevailing soil and climate conditions and expected management inputs is necessary.

The most important management factors are probably the types of planting materials affecting the yield potential and growth and nutrient uptake characteristics, nursery practices affecting the quality of seedlings, early growth and yields, shade regimes which interact very strongly with most other factors and determine the growth and yield that will be obtained, weed control practices determining the extent of competition for nutrients and soil moisture, plant density determining the overall yield and nutrients immobilized as well as pests and diseases which affect the total dry matter production and growth rates and thereby nutrient requirements.

The shade regime and the types of shade trees used are important as growth rates will be affected markedly. The extent of competition by the shade tree could be very significant e.g. in the cocoa/coconut cropping system as compared to monococoa with a nitrogen fixing shade tree such as Gliricidia.

The main climatic factors affecting nutrient requirements are probably the rainfall affecting soil moisture, temperatures affecting overall growth and also degree of moisture stress and light available determining the energy available to the plant for dry matter production and also having a bearing on the soil moisture requirement by the plants.

The third important factor is the soil. Although individual soil properties are measured and determined, they are finally intergrated to determine its ability to supply and store moisture and nutrients for the plant and its properties as a medium of growth for the roots and root activity which determine in turn its ability to exploit the soil moisture and nutrient contained therein.

These factors discussed so far determine the growth and yield potentials for cocoa in an area. An estimate is now required of the nutrients required by the cocoa plant for their growth and yield. Several estimates have been made of the nutrient requirements of cocoa e.g. Thong and Ng (1978), Teo and Chew (1984). These estimates obtained depend on the growth and yield expected under the growth conditions prevailing. It is necessary however to make these estimates to try and quatify the amounts of nutrients that are required and the important nutrients taken up by the plant.

For the purpose of this paper, the data provided by Thong and Ng (1978) i.e. where the nutrient requirements for growth and yield in monoculture cocoa on an inland soil are discussed. Table 8 shows dry matter production and distribution in cocoa plants of different ages. Dry matter accumulation in cocoa increases very rapidly up to the fifth year after planting and stabilizes after that.

The nutrients immobilized in the plant are shown in Figure 4 where the early very rapid growth rate is reflected in the very rapid nutrient uptake especially of potassium and nitrogen in the first 5 years.

Table 8 : Dry matter production and distribution in cocoa plants

(Thong and Ng, 1978)

Figure 4 : Nutrient uptake of cocoa (Ling, 1983)

The total nutrients immobilized in 5 year old cocoa in 2 inland soils in Malaysia when the cocoa canopies have reached the plateau in growth rate are given in Table 9. The very high accumulation in the cocoa plants of potassium and nitrogen is clearly seen. Taking the mean values of 250 kg/ha N and 300 kg/ha K, this is equivalent to 1.1 kg ammonium sulphate and 0.6 kg muriate of potash taken up by each cocoa bush. These nutrients are locked up within the bushes and only become available again to the plant through recycling of the leaf litter and from leaching particularly of K from the leaves in rainfall.

Cocoa leaf litter production and nutrient contents is shown in Table 10. Very high amounts of nutrients are recycled in the leaf litter particularly for N, K, Mg, Ca and after the sixth year. Nutrient cycling is still not high in the fourth year.

Beside nutrients removed from the soil and immobilized in the bushes, nutrients are exported as yield is removed in the pods harvested. The pods have very high nutrient contents equivalent to 31 kg N, 54 kg K, 4.9 kg P, 5.2 kg Mg and 4.9 kg Ca at a yield level of 1 ton dry beans/ha/year (Table 11). The beans are particularly high in N and P and the pods in K contents. The nutrients removed vary with age and yield levels. If the husks are recycled, considerable quantities of nutrients especially K and N, are returned and they have a marked effect on the nutrient availability of the soil as seen in Table 12. Nutrient requirements may then be markedly reduced.

In the monocropping system therefore, the cocoa bushes have very high nutrient requirement for growth and yield, increasing very rapidly in the first 5 years and then reaching a plateau after that with subsequent increases depending mainly on export of nutrients in increased yield. Even then, the nutrient requirements are reduced if husks of the pods which form a very substantial portion of the nutrients removed are recycled to the fields. In addition, in mature areas, nutrient recycling in the litter is significant. Overall nutrient requirements in mature cocoa may therefore not be high.

The above discussion deals with the basic factors involved in estimating nutrient requirements in cocoa. However, as the variables cannot always be assessed accurately, it is useful to employ additional checks to determine if nutrition of the cocoa trees is good. Commonly, the techniques adopted are to check for nutrient deficiency symptoms (Loue, 1962) to sample the leaves and check leaf nutrient levels, to take growth measurements of the cocoa to ascertain the growth rates and also to determine if the yield levels are up to expectation for the agronomic conditions involved.

Nutrient deficiency symptoms are described and illustrated in Wood (1975) and examples of interpretations of leaf nutrient levels are given in Tables 13 and 14 for major nutrients and minor nutrients respectively.

Table 9 : Nutrients immobilized in 5 year old cocoa (Ling, 1983 )

Table 10 : Cocoa litter production and nutrient contents (Ling, 1983 )

Table 11 : Nutrients in pod production (Ling, 1983 )

Table 12 : Effects of pod husks on soil chemical properties (0-15 cm) (Ling, 1983 )

Nutrient deficiencies may be indicated from the analysis results especially in gross deficiencies. However non-nutritional factors eg. pests and diseases or drainage may sometimes affect interpretation. Interpretation of leaf analysis in cocoa is not as advanced as in other crops due to difficulties in correlating leaf nutrient levels with yields, probably a result of the high number of variables which affect leaf nutrient levels in the crop.

After consideration of the above factors, in particular, the growth and yield potential of the cocoa, the amount of nutrients required for the expected growth and yield and the nutrient supplying powers of the soil, it is possible to estimate the nutrients required by the cocoa to attain the growth and yield aimed for and to formulate fertilizer recommendations.

Fertiliser recommendations for cocoa

To draw up the fertilizer recommendations for cocoa, the choice of fertilizers to be used, methods and areas of fertilizer applications and factors affecting efficiency of fertilizers used have to be considered.

There is usually a wide choice of fertilizers available. It is necessary particularly to consider the availability and expected efficiency of uptake of the nutrients in the fertilizers, any possible effects on the soil and finally the cost/unit nutrient uptake which is expected. An example may be urea which is the cheapest N fertilizer. However, volatilization losses of N from this fertilizer may be 30 – 50% and in situations where leaf litter is very thick and the fertilizer applied not to be in contact with the soil, N blow-off may be very nearly complete so that no response is obtained from the fertilizer (HRU unpublished report). Ammonium sulphate as another example is usually considered to be an efficient source of N and leaching losses are lower. However, of the nitrogenous fertilizers, it has the highest acidifying effect on the soil and may therefore not be as suitable as less acidifying nitrogenous such as ammonium nitrate in more acid soil conditions. A final example on the importance of choosing the correct fertilizers is the use of the slowly available rock phosphate. In deficient conditions, high rates are required and the rock phosphate used must be finely ground to ensure efficacy.

The method of fertilizer application may determine the efficiency of nutrient uptake especially in marginal soil conditions. Also the fertilizers should be applied over the areas of active root activities to ensure good uptake. Poor application techniques are detrimental in view of the scorching and damage caused to the superficial root system especially in immature cocoa. Frequent use is made of alkaline materials eg. limestone dust. Interaction between fertilizers may be caused if areas overlap with nitrogenous fertilizer applications. Allowance should be made for this in the areas of application. Recommendations on areas of fertilizer application are given in Table 15. All fertilizers should be broadcast evenly over the areas of application to ensure good uptake by the plant.

After the choice of fertilizers for use and the methods and areas of fertilizer application, it is still necessary to schedule applications to take into account the crop nutrient requirements eg. peak cropping period, competition from weeds, rainfall patterns and soil factors such as topography and susceptibility to erosion to draw up the schedule of fertilizer applications that should be made to ensure maximum nutrient uptake for maximum growth and yield by the plants.

A final step is still required to check the estimated fertilizer requirements against fertilizer trial results available, in particular those that have similar factors affecting growth and yield and similar soil conditions. If these results differ significantly from the recommendations, then a thorough reexamination of the factors assumed should be carried out. Unfortunately, many fertilizer trials published have inadequate details to carry this out meaningfully and therefore they are of limited value. In such cases, in view of the systematic approach carried out in the method drawn up for estimating the fertilizer requirements of cocoa, it is often preferred to stick to the estimates drawn up by the system rather than on doubtful information, the basis of which are poorly known.

Economics of fertilizer application

As fertilizers are costly materials, and as nutrient excess or deficiency affect yields and costs of production, it is necessary to ensure that fertilizer applications are beneficial and economic. This is more easily carried out in mature cocoa areas by checking the results of fertilizer trials and responses obtained in these trials and working out the profitability. Strict economic computations are however not always possible in view of the long term nature of cocoa cultivation and the uncertainty of predicting price levels for the product. For immature cocoa, it is not possible to estimate accurately the economic benefits in view of the lack of crop but the very high nutrient requirements of the plant at this stage and the need to ensure good establishment and a uniform stand justify the high application rates of fertilizers at immaturity.

It is timely here to emphasise again the importance of correct assessment of fertilizer requirements in relation to the other growth factors affecting cocoa and the correct usage of fertilizers as otherwise little or no benefits may accrue from the expenditure on fertilizers.

Conclusion

Cocoa will respond well to fertilizer applications if the management factors, soil and climatic conditions are favourable for good growth and yield and if the soils cannot supply the nutrients required on time. This is in view of the strong interaction between nutrients and the management factors to produce good growth and yields. Fertiliser programmes drawn up consider many factors which are assessed on experience and from trial data and the schedules drawn up should be followed for best results to be obtained.

Table 16 : Recommended areas of fertilizer application in cocoa

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)

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

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

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

* 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.

Cocoa: Pruning

The growth of the cocoa tree has a distinct pattern and differs at different ages. This is illustrated diagrammatically in Fig. 3.

1-4, Stages of the growth of cacao, Theobroma cacao L., Storculiaceae, from Tropical America. -1, Seedling of cacao (copied from Dyant-Najad, 1968). -2, Seedling before the first branching, note the rhythmic branching. 3-, Formation of the first plaglotropic stages. 4-, Adult Cacao. 5-, Base of plaglotropic axes, and the mechanism of the relay in the growth in height, note the parenchymatous dome that terminates the caulomare of the trunk. 6-, Plan of a tier 3 m in diameter, note the articulated structure, the rhythmic growth, and the axillary position of the flowers.

After germination, the seedling grows in height with regular flushes of growth until about 1m to 2m high when upright growth is stopped.

4 to 5 lateral branches (fan branches) are then formed at the jorquette. After a phase of growth, the elongation of growth of the trunk recommences when a new chupon grows out of lateral bud below the jorquette. This new growth is usually vigorous, traverses the whorl of branches and gives rise to a new tier of branches 1m to 2m higher than the first tier or even higher if light is limiting.

If uncontrolled, the above pattern of upright growth can continue for 5 to 6 tiers growing to nearly 10 m high. To make the bushes easier to manage and also to improve yields, it is necessary to control the growth of cocoa by pruning it.

The subject on pruning has been discussed by many authors (Hardy, 1960; Cook, 1966; Chan, 1980 and Jelani et al. 1984)

Pruning requirements differ according to the age and stage of development of the trees and may be briefly described as initial pruning when the trees are establishing, shape pruning to develop a strong well-balanced framework of branches, maintenance pruning to be carried out to maintain a balance between vegetative vigour and fruit production and rejuvenation pruning when vigour and yield of the bushes drop as a result of disease or pest damage.

At all times, pruning should be for a definite purpose as it may be expected that excess removal of foliage will seriously delay growth in young trees and reduce yields in mature cocoa.

The major objectives of pruning are:-

• Height control
• To produce strong/well-balanced framework of branches
• To maintain balance between vegetative vigour/fruit production
• To rejuvenate disease/pest damage bushes
• To promote aeration
• To facilitate access

The above objectives could be achieved through various types of pruning tailored to specific need. The main types of pruning carried out in Malaysia are:-

• Height control pruning
• Number of fan branches pruning
• Water shoots pruning
• Periphery pruning
• Within canopy pruning
• Pest/disease pruning
• Rehabilitation/rejuvenation pruning

For practical reasons, it is necessary to restrict the growth of the cocoa bushes to a manageable height. In Malaysia, the standard practice is to restrict the growth of cocoa to one storey only. However, if the first storey is too low as to hinder field operations, a second storey is allowed to grow. The storey is removed eventually when the second storey is fully developed. Strong dominant branches that grow vertically upward on the fan branches are also removed to restrict height increment (height control pruning).

Some planters prefer to restrict the main fan branches arising from the jorquette to four only. Usually, there are 4-5 main fan branches when the cocoa branches at a jorquette and it is really not necessary to control the number of main fan branches unless they are not balance (number of fan branches pruning).

To cut down unnecessary growths and improve the usage of assimilates, all water shoots arising from the main trunk should be pruned regularly (monthly). It is important that water shoots are pruned at an early stage of growth. They should be pruned as close to the main trunk as possible. Unless they are pruned flush with the trunk, there is a tendency for numerous water shoots to grow from the base of the improperly pruned water shoots pruning could damage flower cushions and reduce fruiting (water shoots pruning).

Once the cocoa bushes are fairly well developed with self-shading canopy, all the low hanging/droopy branches within 1.00 m to 1.25 m from the ground should be pruned to facilitate access and to encourage more upright growths (perihphery pruning).

Finally, the within canopy/shape pruning is carried out produce an ideal bush growth form having the following characteristics:-

• Strong/well-balanced framework of branches
• Minimal unproductive branches i.e. slender/droopy branches with foliage receiving little/no direct sunlight and badly diseased/moribund branches.
• Foliage concentrating mainly close to canopy surface
• Well aerated canopy
• Minimal obstruction to access/harvesting

Once a desired growth form and canopy is achieved, maintenance pruning should be carried out regularly to maintain a balance between vegetative vigour and fruit production.

Sometimes it is necessary to rehabilitate/rejuvenate a mechanically damaged (eg. falling timber when the shade trees are poisoned) or disease damage bushes (eg. advance stage of VSD infection).

In such cases, a basal chupon near the collar region may be allowed to develop into a full bush to replace the damaged/diseased bushes. Budding of such bushes with high yielding clones have also been tried with satisfactory results.

For best results, pruning should be properly timed. The unwanted branches and water shoots should be pruned in their early stage of growths.

For shaping and maintenance pruning, pruning should be carried out before the main flushing and flowering seasons.

It is advisable to practice monthly or even more frequent water shoots pruning when required. The other types of pruning may be carried out at quarterly intervals.

Always maintain a continuous canopy. Never overprune or expose the jorquette.

Pruning to control VSD is a much debated and controversial subject in Malaysia and will be dealt with under pest and disease.

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.

Cocoa: Shade Management Systems

The subject of shade management systems is a rather complex issue. A multitude of shade trees and combinations are possible. Usually a combination of permanent and temporary shade trees are planted to provide shade for cocoa. Common choices are:-

Temporary shade

Currently the preferred shade trees are coconut, Gliricidia, Leucaena and Cajanus.

The choice of a suitable shade system basically depends on the climatic factors (rainfall and soil moisture principally), soil fertility, adequacy of time for shade preparation, presence or absence of existing shade, sufficiency and efficiency of management inputs and objectives of the planting.

Shade management system and practices followed should be designed to :-

• to attain the shade levels required quickly and easily.
• adjust the shade levels to that required easily.
• maintain shade levels as long as required easily.
• not obstruct or hinder other management work in the area.
• allow for shade requirements of cocoa at maturity.

The key elements involved in choice of a shade management system are therefore:-

• time available.
• shade requirement of cocoa planting.
• shade requirement of cocoa at maturity.
• shade material availability.
• labour and management skills available.
• maintenance and management requirements of the shade.
• objectives of the planting i.e. cocoa mono-culture, cocoa/coconuts, etc..

Clean cleared systems

For a clean cleared system where fast growing shade trees have to be planted to provide shade for cocoa, it is usually necessary to plant the shade trees about a year ahead of cocoa. A combination of Gliricidia and Cajanus can provide adequate shade in 6-7 months (Wills, 1980). For the novices, however, it is prudent to plant the shade trees about a year ahead of cocoa to cater for adverse weather conditions and also for other unforeseen problems such as planting failures, pest and disease attach etc.

A shade management system for a cocoa-coconut intercropping system using Gliricidia as temporary shade and MAWA as minimum permanent shade is briefly outlined below as an example:-
Cocoa-coconut intercropping using Gliricidia as temporary shade and MAWA as minimum permanent shade

Planting schedule/pattern

Plant MAWA at 12m x 12m (69 palms/ha) and Gliricidia maculata at 1.5 m x 3.0 m (1800 trees/ha) about a year ahead of cocoa. Gliricidia should not be planted within 3 m from the coconuts. Cocoa at 3m x 3m (1042 trees/ha). The layout of the planting system is illustrated in Figure 2. Should Gliricidia grow poorly, supplementary shade trees such as Cajanus cajan should be planted in pockets at 1.5 m apart along the Gliricidia rows as a stop gap measure.

Gliricidia shade thinning

The above thinning schedule must be considered together with the shade levels suggested for cocoa in Table 4. Thinning should preferably be carried out during the early part of the wet season when the Gliricidia has refoliated.

Fig. 2 Cocoa/Coconut intercropping MAWA as minimum economic shade

Scale :_ 1cm : 3m

Note:- MAWA and Gliricidia planted one year ahead of cocoa

Under existing shade systems

Another category of planting system is to retain some of the existing shade trees as temporary shades such as planting cocoa under thinned jungle, old oil palm and old rubber trees. The retained temporary shade trees to be removed completely in stages as the cocoa matures and as the planted shade trees (usually a combination of MAWA, Gliricidia and Leucaena) could provide shade for cocoa.

Such system usually entails the adjustment of the existing shade to a suitable level prior to planting cocoa. Usually, as much big trees as possible are removed and the desired intermediate and permanent shade trees are planted prior to planting cocoa.

The main advantage of this system is that it obviates the need to establish temporary shade and hence saves time and probably initial expenditure. However, there is a major drawback in the system. The falling timber from the retained oil palm, jungle/rubber trees when they are poisoned can cause considerable damage to the under planted cocoa if too many big trees are retained. The amount of work and costs incurred in rehabilitating the damage cocoa and clearing/staking the fallen timber can be considerable. This is particularly true for planting under thinned jungle and old rubber.

An example of under thinned jungle system using Gliricidia/Leucaena as intermediate shade and MAWA as permanent shade is outlined below and overleaf in chronological order:-

Planting cocoa under thinned jungle using Gliricidia/Leucaena as intermediate shade and MAWA as final permanent shade

1. under-brushing
2. fell all jungle trees with diameter bigger than 15-20 cm
3. clean clear 120 cm wide rentices for planting cocoa and shade trees. Distance between rentices i.e. between cocoa rows at 3.5 m apart.
4. Selectively fell the bigger of the remaining jungle trees in areas where the jungle tree shade is still too dense.
5. Blanket spray the area
6. Plant a mixture of Gliricidia and Leucaena alternately at 3.5 m x 5.0 m (571 trees/ha)
7. Plant MAWA coconuts at 14m x 10m (71 palms/ha)
8. Plant cocoa at 3.5 m x 2.5 m (1142 bushes/ha)
9. Poison all the remaining jungle trees in stages within one year after the cocoa has been planted.
10. Poison all the intermediate shade gradually as the cocoa matures and when MAWA is able to provide shade for cocoa.

As for the other systems, shade thinning must be considered together with the shade requirements of cocoa outlined in Table 4.

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.

Cocoa: Shade and Light

Although cocoa seedlings can be grown in the absence of shade (Cunningham & Burridge, 1960; Lee & Garot, 1971; and Lee, 1978), in most cases, it is usually very difficult to achieve a satisfactory cocoa plantation in Malaysia under fully exposed condition.

Inadequate shade and subsequent moisture stress retards the growth of young cocoa. In extreme cases, 30-50% casualties have been reported. Over-exposure also results in cocoa jorquetting at very low heights thus impeding field access/operations. Another problem excessive light is increased attach by leaf eating insects, particularly cockchafer beetles. Over-exposure also creates problem in weed control.

Over the other hand, excessively shaded mature cocoa produces very poor yields.

The light requirement of cocoa has been extensively reviewed by Owusu (1978). Young cocoa plants grow best at about 30%-60% light, the light requirement of individual leaves on a plant for photosynthesis being met by 3-30% full sunlight.

Harun & Kamariah (1983) reported that for nursery seedlings, the optimal shade regime is 80% shade initially and gradually reduced to 55% shade from the 4^th month onwards.

Murray (1954) reported that best yield was achieved at 50% light without manuring and at 75% light with manuring in Trinidad. Khoo & Chew (1978) noted that the yield of the underplanted cocoa increased linearly with the rate of coconut thinning.

The requirements for light vary between environments and also with the age of the cocoa plants. In general, young cocoa plants require more shade than those with well developed and self-shading canopy. Cocoa grown on fertile soils located in areas with little moisture stress also requires less shade.

For good results, shade regimes must be adjusted to suit the stage of growth of cocoa, soil fertility as well as the environmental conditions.

A suggested shade regimes suitable for Malaysian conditions is given in Table 4.

Table 4 : Suggested % shade levels for cocoa

N.B. : These are expected theoretical % shade levels for best establishment, growth and yields under each condition. Practical considerations, in particular damage from retained initial overhead shadewhich is poisoned out after the first year, however make it necessary often to modify these levels. Other management practices are than implemented to offset the setback from the less than optional shade conditions.

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.