The World's Worst Cocoa Problems

Cocoa has been described as a “virtuous crop”. There is an increasing appreciation of its value for: land rehabilitation, enrichment of biodiversity (of previously cleared land) and provision of sustainable incomes in less developed regions. Like other crops though, it can be attacked by a number of pest species including fungal diseases, insects and rodents – some of which (e.g. frosty pod rot and cocoa pod borer) have increased dramatically in geographical range and are sometimes described as “invasive species”.

• The global threat of invasive fungal diseases
  (Phytophthora and Moniliophthora diseases)
• Africa: mirids (capsids) and swollen-shoot virus
• South-east Asian cocoa problems (e.g. cocoa pod borer)
• The globally chronic problem of vertebrate attacks
• Estimates of cocoa pest severity
• What we are doing about them?

Invasive species

Fungal diseases are a principal constraint to world cacao production and on a global scale the greatest losses are result from black pod rots – caused by Phytophthora spp. (see below). Two basidiomycete fungal diseases – witches’ broom and frosty pod rot – pose a special threat to livelihoods in Latin America. Black pod rots currently cause the greatest loss of production, but estimates of severity perhaps underemphasise the potential importance of frosty pod rot: Moniliophthora roreri.

Some cocoa problems have a world-wide distribution, others are restricted to individual cocoa growing regions in: the Americas, Africa and S.E.Asia.

Black pod: Phytophthora spp:

Phytophthora palmivora: Brazil

Phytophthora spp. belong to the water moulds (Oomycete) group of diseases, that cause black pod in cocoa. They are not fungi, but are controlled with products that are often called “fungicides”.

Control measures

Stem canker caused by P palmivora (Viet Nam)

Phytophthora megakarya: Cameroon

In Africa, P. megakarya has become a major invasive disease, having spread from central region westwards to Ghana and the Ivory Coast.

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Invasive Moniliophthora diseases:
Frosty pod rot Moniliophthora roreri

Frosty pod rot of cocoa

M. roreri on various Theobroma spp.

Latin American problems but a global threat …

Control measures

Frosty pod rot is an invasive disease which, originally identified in Ecuador in 1917, spread rapidly to other countries in Latin America during the 1970s. Producing large quantities of powdery spores, it has a high potential for transmission and thus further extending its range. Infested plantations may suffer dramatic yield loss, leading to neglect of trees by farmers and complete loss of production.

Frosty pod rot (M. roreri): early symptoms

Witches’ broom
Moniliophthora (= Crinipellis) perniciosa

Witches’ broom cushion gall

Classic witches’ broom

The fungal pathogen that causes witches’ broom disease has now been identified as a close relative of frosty pod rot, and they have now been placed in the same genus: Moniliophthora

M. perniciosa: pod lesion

Basidiocarps: formed under very moist conditions

Other cocoa pod diseases

Warty pod rot: a relatively local problem in W. Africa

Botroidiplodia theobromae (Brasil)

Insect-borne viruses

Cocoa swollen shoot virus (CSSV) symptoms

Control measures

CSSV is transmitted by mealybugs (Pseudoccidae) including Planococcoides njalensis and species in Planococcus, Phenacoccus and other genera.

Vector: Planococcoides sp. tended by a black ant

Mistletoe in cocoa provides a habitat for a certain species of ants that “farm” mealy bugs, (other ant species may be beneficial). The presence of mistletoe also favours infestation by mirids.

Vascular streak die-back (VSD):
Oncobasidium theobromae

Vascular streak die-back (VSD): Oncobasidium theobromae: characteristic staining of vascular bundles in an excised leaf attachment (left: upper branch) streaking of bisected young stem (left: lower branch).

 
Mottling of a leaf on an infected stem that was insufficiently pruned at the first sign of infection (left) and “saw-tooth” leaf lesions (right).

Root diseases

Fungal diseases in the soil, such as Ceratocystis fimbriata and Roselinia spp. can cause relatively sudden tree death. The latter have been important when associated with cocoa germplasm collections.

Ceratocystis wilt of cacao, caused by a host-specialized form of the fungus, has been locally important in Latin America, where it is believed native and called mal de machete. Its importance in Brazil has been recognised increasingly since 1998 and has been associated elsewhere with drought, with South Bahia experiencing reduced rainfall in recent years. Xyleborus beetles are attracted to the diseased trees and bore into the branches. The frass from beetles is pushed to the outside of stems as a light, powder and contains viable inoculum of the fungus, which may be spread by wind or rainsplash.

a. West African Miridae (capsids)

Control measures

Typical capsid lesions on pods.

The greatest damage is to the tree itself, with destruction of growing shoots (above left) and whole trees may be killed.

Helopeltis spp.

Helopeltis (Afropeltis) bergrothi: probably does less damage than other capsids in Africa, although being more “apparent” to some farmers.

In some parts of S.E. Asia, other species in this genus such as Helopeltis theivora (= H. theobromae) and H. antonii are serious enough to spray regularly with insecticides.

b. Pentatomidae

Bathycoelia thalasina
(taken in Ghana)

Although less damaging than mirids, shield bugs such as B. thalassina feed on developing pods via their very long stylets – resulting in damage to the beans themselves. Pods become distorted and Entwistle (1972) reported that up to 40% pod loss may occasionally occur with Amazon and hybrid cocoa.
                   

Cocoa pod borer (CPB)
Conopomorpha (=Acrocercops) crammerella

CPB: characteristic mottling of pod
(showing entry hole)

CPB: Conopomorpha crammerella: internal infestation

Adult CPB: in typical resting position underneath a horizontal branch

Stemborers

Zeuzera spp include Z. coffeae: larvae of leopard moths (Cossidae) that bore into trunks of many tree species. The galleries formed are especially damaging to young cocoa, often causing the snapping-off of smaller branches.

Zeuzera sp.: locally-serious S.E. Asian pests belonging to the Cossidae.
Eulophonotus spp. may be a problem in Africa.

In Papua New Guinea (PNG) one of the major pests are two species of longicorn beetle (Cerambicidae) Glenea spp. (G. aluensis from New Britain shown here). Longicorn larvae are often recognisable by the enlarged, flattened segments just behind the head capsule.

Control measures

In PNG and Tuvalu, striking, flightless weevils (Curculionidae) belonging to the genus Pantorhytes are primary cocoa pests. Often tunnelling in numbers around the jorquette and branches, they may be also responsible for ring barking and killing whole branches.

Adult and larva in gallery of Pantorhytes pluteus taken in New Britain, PNG. Both Pantorhtes and longicorn beetles (left), besides causing damage to trees themselves, may introduce diseases such as Phytophthora palmivora cankers: possibly resulting in tree death.

Rodents and other vertebrate pests

 
Damage probably caused by a squirrel (left) and a rat (right)

Woodpecker hole (Costa Rica)