Changing the Face of Cocoa Plantations – Part 2Sreenivasan,T.N. 2015.
Edited by Dr. Marissa Moses and Dr. Lambert Motilal (Cocoa Research Centre, The UWI St. Augustine Campus) of a Paper presented at the International Fine Cocoa Innovation Centre Conference & Symposium, Trinidad and Tobago, March 23-24, 2015.
In an industry where every bean counts, devastating losses from disease can lead a cocoa plantation to ruin.
You are in a city where a highly contagious disease is spreading. Infection is a numbers game and you are aware that the probabilities can be reduced if you have a strong immune system, wash your hands with soap frequently and distance yourself from sick persons. In short, you will implement a diseases management strategy.
In our last article (Changing the Face of Cocoa Plantations- Part 1 [provide hyperlink] a new system of laying out cocoa plantations is being proposed by researchers at the Cocoa Research Centre (CRC). Among the numerous factors which the agronomists must balance to obtain higher yields in a sustainable environment, proper disease management is crucial.
Cocoa suffers from infectious diseases wherever it is grown. Black pod disease, caused by several species of Phytophthora is the only major economically important disease which is universally present. Other diseases are restricted to distinct geographical areas. Major diseases include Witches’ broom, Frosty pod, Swollen shoot and Vascular-streak dieback. In Trinidad and Tobago and a few other West Indian island states, Black pod and Witches’ broom disease are the major diseases present. In Trinidad and Tobago, two species Phytophthora (P. palmivora and P. tropicalis [= P. capsici] are reported on cocoa (Figure 1). Of these P. palmivora is the more widely distributed and predominant species. Witches’ broom disease is however not as economically damaging due to the widespread use of tolerant hybrid genotypes.
Most of the cocoa plantations in Trinidad and Tobago are over 50 years old and have ageing, low yielding trees. This low yield is partly due to poor management, neglect and improper or lack of cultural practices in the plantations. Losses to this crop from disease especially black pod, are phenomenal, reaching sometimes near to 100% depending on rainfall. In an industry where every bean counts, devastating losses from disease can lead a cocoa plantation to ruin.
Conditions which favour black pod disease are: susceptible genotypes, extended rainy periods, high humidity, impeded drainage and heavy shade. As free water is essential for the black pod disease cycle, measures which prevent or reduce availability of water will help to minimise black pod incidence. These objectives can be achieved by using resistant or tolerant genotypes, good field layout with rapid drainage and proper spacing of trees to reduce humidity levels. Use of shade trees with the desired architecture (tall trunk with a compact canopy) would facilitate the optimum intensity of light. Field sanitation is also essential to limit the spread of the disease in the Cocoa Orchard System. This involves frequent harvest, removal of infected pods and plant parts, and effective pruning practices to maintain an open canopy which will allow free air movement, within the plantation.
Black pod disease is also reduced by the use of synthetic chemicals (fungicides). Fungicides could be protective or systemic in their action and applied to plants through various systems of application. Some of these are: high or low volume sprays, single or multiple applications, injections and the CRU Collar method of fungicide application. However, chemicals that control cocoa diseases can cause possible contamination of beans and environmental pollution. Recent emphasis is on the use of biocontrol organisms such as antagonistic fungi, bacteria and endophytes, which have the ability to reduce the severity of the diseases. Some of the biocontrols that are suggested are the plant growth-promoting rhizobacteria (PGPR), such as Pseudomonas fluorescens (Figure 2.) which is capable of suppressing or preventing phytopathogen damage.
Good practices for managing diseases in the Cocoa Orchard System based on preventive measures include the use of disease resistant/tolerant genotypes, a good field layout with optimum spacing, rapid drainage system, shade trees with the desired architecture, limiting cocoa tree height and maintaining an open cocoa canopy. A shallow basin for organic mulch seeded with biocontrol agents at each tree base, along with an on-tree reservoir of biocontrol agents will help to prevent or retard infections and establishment possibilities of pathogens. Adoption of these methods very early in Cocoa Orchard development would prevent on-tree establishment of pathogens.
To read more about such studies we recommend:
- Bailey, Bryan A., and Lyndel W. Meinhardt, eds. (2016) “Cacao diseases: A history of old enemies and
- Panpatte, Deepak G., Yogeshvari K. Jhala, Harsha N. Shelat, and Rajababu V. Vyas (2016). “Pseudomonas fluorescens: A Promising Biocontrol Agent and PGPR for Sustainable Agriculture.” In Microbial Inoculants in Sustainable Agricultural Productivity, pp. 257-270. Springer India.