Page 7 - Vol.39-No.1

CROP PROTECTION

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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