ACRI - Cocoa Pests and Diseases
Threat of Disease:
Pests and disease cause approximately one quarter of the world's cocoa to be lost – some half a million tons. This is due to three problems: fungal diseases, insect damage and viruses. The majority of this damage is however, limited to fungal diseases, which are easily spread by spores, and now more so because of increased air travel to otherwise isolated parts of the world where cocoa is grown. The impact of pests and disease is a serious problem for the cocoa industry, with crop losses of about 30-40% each year. Considerable resources are being devoted to this problem by ACRI.
Witches Broom (Crinipellis perniciosa):
A fungal disease, which infects the trees and is carried by spores. It causes broom-like stems that grow from branches, although its first visible signs are on the small clumps of flowers called flower cushions. Flower stems appear thicker than normal and some flowers are wilted and brown but will not fall off the tree. Later, the vegetative brooms appear, growing either from the flower cushions or in the canopy growing from infected branch tips. After the initial growth spurt, the infected branches turn brown and die from the tip back toward the tree. Finally, small mushrooms grow on the dead brooms, releasing spores that infect other trees. As the broom growth is accelerated and uses much of the tree's energy, fewer pods are produced and those that are, often show signs of disease which result in inferior or even valueless beans.
Witches Broom has caused devastation of Brazil's cocoa crop but has not yet been seen outside of the Americas.
Monilia Pod Rot (Moniliophthora roreri):
This is a fungal disease that attacks only young growing pods. It is difficult to detect in its early stages but once infected, the pods become irregularly swollen, then discolored and then grow spores on the surface which are released after rains for up to 10 months and can travel great distances on clothes and shoes. The spores are much smaller than those of Witches Broom and are far more resistant to environmental factors such as dry heat and intense, direct sunlight.
Consequently, it is likely to be a much greater threat than Witches Broom. Monilia first appeared in Ecuador, then spread across the Andes to Amazonian Ecuador and Peru. It is predicted to infect Bahia in Brazil within a decade.
Cocoa Pod Borer:
This is a small insect about 1 cm long which flies like a mosquito. The female lays a tiny egg on the furrowed surface of the pod. After a few days the egg hatches, a larva emerges and burrows into the pod, spoiling the beans inside. The pod dries up after the larva has fed on the pulp and its entry hole allows infections to rot the pod. Approximately two weeks after hatching, the larva leaves the pod, usually producing a silk thread with which to reach the ground.
Several control methods are being tried – pruning to allow more sun to reach the tree; frequent and regular harvesting of the pods; utilizing species having a thicker sclerotic layer to discourage entry and cultivating beneficial predatory wasps. This insect is common in South East Asia, especially in Malaysia and Indonesia.
Black Pod (Phytophthora Pod Rot):
This is a fungal disease affecting trees grown in humid conditions. There are two strains of the disease: Phytophthora megakyrya is the faster moving and thereby the more dangerous is currently restricted to Cameroon, Nigeria and Ghana. Phytophthora palmivora acts more slowly and is thereby more easily controlled. Both strains attack all parts of the plant but this is most pronounced on the pods, which develop dark brown lesions, later becoming dusted with white spores. It is further spread by rain. Both strains may be controlled by selective pruning of diseased pods together with the use of copper fungicides.
Vascular Streak Dieback (Oncobasidium theobromae):
This is another fungal disease found predominantly in Southeast Asia. It essentially causes branches to dry up and die from the tips backwards. It begins with green spots on yellow leaves, mainly on the middle of the branch for mature trees, but on seedlings, all the leaves may be affected. The bark of the tree becomes rougher and eventually all the leaves fall from the branches with white spores being released from the leaf scars, spread by the wind, which need rain to infect more trees. Generally, pruning can help older trees, but trees less than five years old cannot survive.
Cocoa Swollen Shoot Virus:
Small insects called mealybugs cause this virus, which has been limited to Ghana and Nigeria. Ants, which share a symbiotic relationship, protect the mealybugs. Although ultimately swelling of the root and stems occurs, its first indication is seen on the leaves as a different coloring of the vein system as well as sometimes, an irregular pattern on the leaf surface. Biological control such as exterminating the ants has been unsuccessful thus far.
For more information:
Visit Ohio State's
Integrated Pest Management (IPM) Webpage
(Contact: Dr. Roger Williams),
Ohio State University
The Biscuit, Cake, Chocolate and Confectionery Alliance (BCCCA), UK
Malaysian Cocoa Board's site: Cocoa Diseases and their Management
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Biotechnology WG |
Sustainable Cocoa Supply WG
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