Page 7 - Vol.39-No.1
P. 7


                                                  PEST, DISEASE AND WEED

                                                  INTERACTIONS IN COCOA

                                                     (THEOBROMA CACAO)

                                             PART 1 COCOA IN THE SHADE.

                                            producers of this New World tree-crop   Quality shade is more or less essential
                                            commodity are Old World countries such  for cocoa and especially the temporary
                                            as Cote d’Ivoire, Ghana and Nigeria in West  shade provided for cocoa nurseries and
                                            Africa and Malaysia and Indonesia in South  newly planted stands which require only
          DR. TERRY MABBETT                 East Asia.                          one quarter of full intensity sunlight. Cocoa
                                              The small island of Trinidad at the south-  trees grown within properly designed and
          Cocoa (Theobroma cacao) faces more                                    managed stands provide a large measure of
        complex and interactive pest, disease   ern end of the Caribbean Sea was once   mutual self-shading and will form ‘closed’
        and weed problems than any other trop-  one the world’s largest producers of cocoa   canopies that keep out a significant pro-
        ical tree crop.  Theobroma genus (plant   although today’s commercial production is   portion of the sunlight.
        family Malvaceae) comprises a group of   miniscule by international standards. Most
        naturally, short-stature trees native to the   of the world’s definitive research and de-
        rain forests of the Amazon Basin and oth-  velopment into botany and agronomy of
        er regions of Central and South America.   cocoa was carried out in Trinidad during
        Some have been harvested in the wild for   the 19th and 20th centuries, first at The
        thousands of years by Amerindians (Native   Imperial College of Tropical Agriculture
        American Indians), but T. cacao which is an   (ICTA) and more latterly in the Cocoa Re-
        under-storey tree of the Amazonian rain   search Unit and Departments of Botany
        forest is the only species to have been   and Crop Science at the University of the
        cultivated on a world-wide scale.   West Indies (UWI).
          Cocoa started to spread from its Centre   Trinidad is home to the Internation-
        of Origin in the sixteenth century carried   al Cocoa GeneBank (ICGT) regarded as   A good crop of cocoa in the making
        mainly by the Spanish and Portuguese,   the most valuable collection of cocoa   (Picture Dr Terry Mabbett)
        first into Venezuela, Caribbean islands   germplasm in the world and comprising   On balance cocoa does best when the
        like Trinidad (1525) and Jamaica and then   around 2,200 accessions and represented   crop is provided with at least some per-
        right into South East Asia and the Indian   by some 12,000 cocoa trees. Many of the   manent shade and not only for growth,
        Sub-Continent.                      pictures of cocoa which appear in this and
                                            the following two articles Part I, II and III   development and yield. Permanent shade
                                            were taken in Trinidad.             minimises physiological stress and protects
                                                                                trees from insect pests like mirids that can
                                                  Cocoa in the shade            easily be antagonised into major pest sta-
                                              Theobroma cacoa is a wild tree tak-  tus when exposed to high light conditions.
                                            en  from its  natural,  deep-shaded,  low-  By the same token the range of fungal
                                            er-storey environment in the Amazonian   and fungus-like pathogens which cause
                                            rain forest and grown on a truly massive   disease in cocoa is largely a reflection of
                                            scale, mostly in monocultures, right across   the shady, moist and high humidity con-
                                            the humid tropics. The first cocoa estates   ditions created and maintained under the
                                            were established in forested areas where   tree canopy. As a relatively slow-growing
           One of many cocoa accessions in the   the required shade could be provided by
           International Cocoa GeneBank (ICGT)   leaving some tall forest trees in situ when   and shade-loving tree cocoa cannot com-
           on the island of Trinidad in the West                                pete with the fast-growing and sun-loving
            Indies, and showing unusual shape,   the virgin forest was cleared and planted   plants whether grasses, herbaceous di-
          colour and surface pattern of the cocoa   with cocoa.
              pod (Picture Dr Terry Mabbett)                                    cotyledonous weeds or other shrubs and
                                              But new cocoa is invariably planted on  small trees.
          Cocoa was a relatively late arrival into   previously cropped land and can never be
        Africa, first recorded on the West African   provided with the natural, quality shade   As a small tree occupying the under-sto-
        island of Fernando Po in 1855, from where   normally received when growing naturally   rey niche, cocoa is shaded by a large num-
        it was introduced into mainland West Afri-  in its evergreen rainforest environment of   ber of different tree species at varying
        ca around 1879. Most of today’s biggest   the tropical Americas.        heights  in  the  rainforest  canopy.  When

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