Pest and Disease Management in Cocoa

David Guest, Professor of Plant Pathology, The University of Sydney, Australia

The major international cocoa processor, Barry Callebaut, recently warned that annual cocoa production in 2020 would have to rise by 25%, or 1 million tonnes, to keep pace with the rapidly increasing demand for chocolate in the developing economies of China, India, Eastern Europe and Brazil. However our ability to sustain even current production levels is threatened by climate change, land degradation, political instability, alternative crops, labour shortages and pests and diseases.

Cocoa is affected by a range of co-evolved and new confrontation diseases and pests that can destroy entire crops. Witches’ broom (Crinipellis perniciosa) and frosty pod rot (C. roreri) are two diseases localised in South and Central America, while Vascular-streak dieback (Ceratobasidium theobromae) and cocoa pod borer (Conopomorpha cramerella) are restricted to the Asia-Pacific region, and cocoa swollen shoot virus is only present in Africa. Several Phytophthora species cause pod rot, canker and blights wherever cocoa is grown. These problems, together with a number of minor pests and diseases, reduce global cocoa yield by up to 40%.

Cocoa breeders boast of genotypes that can produce several tonnes of beans per hectare, however in most countries farmers only average 10% of potential yields, largely because of the cumulative effects of disease, pests and declining soil fertility. Disease reduces global cocoa production by up to 40% annually, and in some areas causes total crop loss. Brazil, previously one of the top three cocoa producers, had its production decimated by witches’ broom disease in the 1990s, and much of South America is currently threatened by the spread of frosty pod rot disease. While the soils of newly-cleared forests are usually fertile and support yields well over a tonne of dry cocoa beans per hectare for a few years, organic matter and nutrients are rapidly exhausted if not replenished by fertilisers, and yield declines steadily after trees reach an age of ten years.

For many semi-subsistence smallholder farmers cocoa trees signify land ownership and function like a dependable ATM that can be visited when school fees or hospital bills need to be paid. These farmers depend on their own food gardens or earn an income from other employment. To impoverished farmers the poor and unreliable returns from cocoa do not justify investment, and even if they had the resources farmers frequently lack informed and objective technical or logistic support to decide what investment is needed. Older farmers are risk-averse and less likely to change their farming methods, while more entrepreneurial farmers are lured by alternative, and more lucrative, crops such as rubber oil palm and maize. Supporting these farmers to invest in improved productivity is the key to making sure production continues to meet demand.

In Indonesia and Papua New Guinea work funded by ACIAR involving LaTrobe and Sydney Universities in Australia, Hasanuddin University, the Assessment Institute for Agricultural Technology, the Indonesian Coffee and Cocoa Research Institute in Indonesia, and Mars Australia, focuses on working with farmers and local research and extension agencies to identify constraints to production, devising a series of management options for farmers then working with farmers and extension workers to promote the adoption of these options. The first level of improved management aims to stimulate flowering and reduce disease pressure by implementing pruning, sanitation and regular and complete harvesting. The second level is to provide nutrients to support the development of flowers into pods, and the highest level includes the targeted use of pesticides to protect developing pods. Management levels are demonstrated side by side in villages, and are managed by the farmer who was trained to implement each level. That farmer provides advice on the cost and effort provided as well as the increased yield experienced, supported by regular visits from extension workers. Field Days are also used to promote the options, but the choice of management level is made by the farmer. In our experience farmers quickly adopt improved management because they see the results and are able to discuss the effort required with their peers.

These management options are based on solid research. The second part of our strategy is to support local scientists to engage with industry stakeholders, including of course farmers, to identify constraints and to develop research that addresses them. Engaging private sector champions in promoting improved management is essential to the sustainability of farmer training. Results from collaborative research activities build local capacity and feeds directly into refining management options for farmers.

The key sustaining our chocolate dependency is to improve the sustainability, productivity and viability of smallholder cocoa production by supporting farmers, extension workers and scientists working with the industry. A well-supported cocoa industry is a powerful driver of rural poverty alleviation, and increased yields contribute directly to improved health and living standards, reduced pressure on rainforest clearing and political and social stability.