New combat strategies for cocoa
Cultural and agronomic practices have become increasingly important in the production of cocoa as the battle against insects, diseases and weeds continues to present a major challenge for small-scale farmers. New advances in disease-resistant varieties, biological control and semiochemicals also provide farmers with alternative methods of control to the excessive use of pesticides which have been used in the past.
The advantage of an integrated pest management system for cocoa, as with other crops, is not only the reduction in the use of chemicals but that IPM can offer an economic incentive to growers by the increase in quality that can be achieved. However, accurate pest management is dependent on a strong scouting program. Farmers need to know the conditions of their crops and the pests in the field so that they can determine the best actions to take. Monitoring techniques include recording climatic conditions, particularly temperature and humidity, recording and surveying the crop for signs of pests or pest damage, and use of insect traps to identify pests. Systematic scouting data should then be recorded so that it can be used for deciding a particular course of action. For instance, some pest damage can be tolerated by a plant without detrimental effects to the crop but a farmer should be aware of increasing levels of the pest before it presents a major problem.
There are numerous insects in the field which damage the quality and quantity of cocoa beans and that hinder the production of cocoa. The single most important insect is the cocoa pod borer of SE Asia. Next in importance would be the mirids, also known as capsids. The mirids differ between regions but they are a major problem in most cocoa growing regions.
Alternative control methods that are currently being tested for cocoa pod borer includes a regime involving pruning plus Complete, Frequent, Regular Harvesting (CFRH) which has been shown to be highly effective in increasing yields and reducing pest damage. Indeed the Cocoa Pod Borer Management Project, supported by ASKINDO, ACRI and BCCCA, has shown that yield can be increased by up to four fold using this technique. The CFRH ensures that pods are harvested when the pest larvae are still inside the pod and can be destroyed before they have a chance reproduce. The pruning is important in allowing light penetration to maximize the photosynthetic efficiency of the tree canopy and also allows all pods to be seen and harvested as soon as they ripen. This is very important since ripe pods left on the tree allow the pest to complete its life cycle and lead to increased numbers of insects. The Malaysian Cocoa Board is currently exploring the cultivation of beneficial predatory wasps (Trichogrammatordia spp.); initial trials have demonstrated a cost-effective reduction in crop loss which was comparable to levels achieved with chemical control. Finally, utilizing species which have a thicker sclerotic layer to discourage entry of the pod borer may also be effective in reducing pest numbers.
In West Africa, the Cocoa Research Institute of Ghana (CRIG) has initiated a project to develop an IPM strategy for the control of cocoa stem borer (Eulophonotus myrmeleon) which has become a major pest throughout the country. The IPM involves the use of Gastoxin, a fumigant paste of aluminum phoshide, and cultural practices. Ants are also thought to be useful beneficial predators. Studies have also been instituted by CRIG, in collaboration with British and American cocoa institutions, to evaluate natural enemies in Ghana for control against mirids. Beauvaria bassiana has been reported to be lethal to some mirid species in Malaysia so other fungal pathogens of mirids, such as Bacillus and Apergillus spp. may also have potential for biological control.
Black pod or Phytophthora pod rot is the primary fungal disease affecting cacao production worldwide. Witches' broom, Crinipellis perniciosa, is a serious fungal disease of cocoa in Latin America. Indigenous to the Amazon, it is now present in most of the cocoa growing regions in South America and several Caribbean islands. Monilia Pod Rot, Moniliophthora roreri, is another serious fungal disease which is confined to the Americas. Its range includes northwestern South America including Ecuador, Colombia, and Peru, and southern Central America. It is expected to infect Bahia in Brazil within a decade - a region which has already had its cocoa production ravaged by witches broom. Other serious diseases of cocoa include Vascular Streak Dieback (Oncobasidium theobromae), a fungus disease of SE Asia and parts of the Far East, and Cocoa Swollen Shoot Virus which infects cocoa trees in West Africa.
For black pod disease, cultural techniques such as shade reduction, regular harvesting and frequent weed control may reduce infection, but some losses from black pod are almost inevitable in areas of very high humidity. As with monilia pod rot and witches' broom, frequent 'sanitation' sweeps to remove infected material is advisable. Liming the soil to reduce pH to 6.0-6.5 may also help to keep Phytophthora inoculum levels low. Resistance breeding for the disease is currently a major priority in West Africa where the virulent P.megakarya (See Blackpod pathogens revealed) is proving difficult to control. The current CRIG programme includes evaluating clonal plants from trees which have escaped infection in areas severely infected with P.megakarya to assess whether these plants are intrinsically resistant or "escapes": trees that produce the bulk of their crop when climatic conditions are least conducive to the spread of the disease. In addition there is a project supported by CAOBISCO which involves researchers in CIRAD (France), CRU (Trinidad), CNRA (Côte d'Ivoire) and IRAD (Cameroon) to identify factors involved in black pod resistance and use molecular markers (Quantitative Trait Loci) to assist in the development of disease resistant varieties.
Durable resistance offers the best potential for management of witches' broom. Effective screening of germplasm for resistance to witches' broom is in progress at CEPLAC, Itabuna, Brazil, and at INIAP, Pichilingue, Quevedo, Ecuador. The best resistant germplasm will be used to produce resistant planting stock. However, this is a time consuming process and CEPLAC is also investigating the potential of biological control using antagonistic fungi such as Trichoderma spp. A pilot plant for commercial scale production of this bio-agent is currently being installed for field use.
For monilia pod rot, cultural practices are currently the most effective means of combating the disease. The most important of these are the regular removal of diseased fruits, the pruning of cocoa and shade trees, and the installation of effective soil drainage systems. Studies continue on the use of resistant material but have yet to produce results that could benefit producers. Recently an initiative supported by USDA and ACRI to investigate biocontrol has been started in Peru, Costa Rica and the UK.
Sound agronomic knowledge about the plantation (tree spacing, shade, soil fertility, nearness to neighboring diseased plantations, incidence and severity of pests and disease in the plantation, time of harvest, pruning intensity) is also essential for good management and the sustainable production of cocoa. It is evident that a range of IPM methods is currently available to farmers but it is equally apparent that a distinct lack of extension exists at farm level across the smallholder community. The challenge now is to develop extension systems which are cost effective and are able to empower thousands of small-scale farmers in IPM strategies. Farmer-participatory training systems, like the Farmer Field Schools which have proved successful in the production of coffee in Kenya, may provide a solution.
ASKINDO - Indonesian Cocoa Association
BCCCA - Biscuit, Cake, Chocolate and Confectionery Alliance of the UK
CAOBISCO - Association of the Chocolate, Biscuit and Confectionery Industries of the EU