UNIVERSITY OF HORTICULTURAL SCIENCES, BAGALKOT

Pest and Diseases of Cocoa

Chandalinga

UHS11PGM139

KITTUR RANI CHANNAMMA COLLEGE OF HORTICULTURE, ARABHAVI

Presentation on

Diseases Seedling die-back Phytophthora palmivora White thread blight Marasmius scandens Black pod disease Phytophthora palmivora Charcoal pod rot Botryodiplodia theobromae Witches' broom Crinipellis perniciosa Swollen shoot Cocoa swollen shoot virus

Minor diseases : Pink disease Pellicularia salmonicolor Stem canker Phytophthora palmivora Monilia pod rot Monilia sp. Cherelle rot Colletotrichum gloeosporioides

Seedling die-back:

Symptoms:

This disease is more severe on one to four months old seedlings.

Infection may start from the tip of the stem or from cotyledonary

stalk or from the collar region.

The disease appears as dark brown to black, water soaked, linear

lesions.

This lesions extend to the leaves through petiole result in wilting

and subsequent defoliation of the seedlings.

In advanced stage die back of the seedlings.

Etiology:Phytopthora palmivora

The mycelium is septate and 7 µm in dia., sporangiophores are

simple or branched.

Sporangia are inverted pear shaped, terminal and measure 38 to 72

µm × 33 to 42 µm.

Zoospores are 8 to 10 µm in dia. Oospores are spherical and

measure 33 to 45 µm in dia.

Management:

All the infected seedlings in the nursery should be removed and

destroyed.

The disease can be controlled effectively by providing adequate

drainage.

Soil drenching with Bordeaux mixture 1.0 per cent or copper

oxychloride 0.25 per cent.

A combination of seed dressing and soil drenching with Kocide at a

concentration of 0.91 kg in 45 litres of water effectively controls

pre- and post-emergence seedling death.

White thread blight

Severe incidence of white thread blight in India was noticed in 6 months

old seedlings in the nursery in Karnataka during 1990.

The young branches of the affected plants contain white mycelial

threads of the fungus which spread longitudinally and irregularly

along the surface of the stem. The growth of the fungus is very rapid

on the stem under favourable conditions of high humidity and

entered the leaf at the nodes along the petioles. The fungus invades

the cortical tissues which eventually turn dark brown to black. The

diseased leaves also turn dark brown. The dead leaves in a branch

eventually get detached from the stem but are found suspended by

the mycelial thread in a row. The extensive death of the young

branches and suspended leaves in rows are the common field

symptoms of white thread blight.

Symptoms:

Causal agent: Marasmius scadens

Mode of spread and survival: The disease spreads from plant to plant and to different branches of the same plant through the mycelium. The dead leaves with the mycelial mat can be easily carried by wind on to the leaves and stems of the healthy plants and initiate the disease.

Epidemiology: High humidity, less aeration and sunlight due to thick shade are the predisposing factors for the occurrence of white thread blight disease.

Management: Damage can be reduced by removal of the dead materials and pruning of affected parts. Shade reduction and some structural pruning of branches are necessary to reduce the humidity in the canopy and the disease.

Cocoa pods may be attacked at any stage of their development.

Infection of the pod may be proximal (stalk end), distal (tip) or

lateral (sides).

First sign of the disease is appearance of brown spot on the pod.

The brown discolouration rapidly spreads in all directions. Usually,

there is a line of demarcation of diseased and healthy tissues. The

discolouration spreads over the whole pod. Under humid conditions,

a white mould appear on the surface of the pod.

Internal tissues of diseased pods become brown. Infected beans are

discoloured.

Causal agent: Phytopthora palmivora, P. megakarya, P. capsici

Black pod diseaseSymptoms:

Epidemiology:

The fungus is disseminated by wind-borne spores which are

produced on infected pods. The spread is also by splashing rain,

rodents and by contact between healthy and diseased pods. Ants

have been found to spread the disease. The fungus persists as

mycelium in infected cushions and pods and as chlamydospores

during dry weather.

The fungus infects chillies, citrus, coconut, cotton and rubber.

Mode of spread and survival:

Pods of all ages are susceptible. Closer spacing between trees,

damp locality and cool damp weather favour the rapid spread of the

disease. The disease spreads rapidly under conditions of high

rainfall and long periods of high humidity. Pods and other tissues

damaged by insects, rats, man etc. are highly susceptible to

infection. Bark damage is necessary for wood infection and canker

development.

Epidemiology:

Important control measures are regular removal and destruction of

infected pods at weekly intervals, during the rainy season pruning of

shade trees.

Proper pruning of cocoa trees is also very essential to minimize the

shade. These operations reduce inoculum as well as the disease.

Spraying just before the onset of monsoon with Bordeaux mixture

1.0 per cent or copper oxychloride 0.25 per cent and then at

intervals of two weeks during the peak period of incidence along

with weekly removal of infected parts give better control of the

disease. Spraying with captafol or fentin acetate or metalaxyl or

aluminium ethylphosphonate is also effective. Spray should be

directed at the pods and bearing branches. Resistant varieties if

available can be used. Lafi No.7 and Sic.28 are resistant clones

reported from Samoa and Brazil respectively.

Management:

Charcoal pod rot is found throughout the year. But the disease is

severe during summer months.

Pods of all ages are susceptible.

Symptoms: The disease occurs on wounded pods or pods

which are" under stress. The infection takes place through wounds

generally caused by insects and rodents. The infection appears as

dark brown to black spot on any place on the pod surface and

spreads rapidly. The whole mass of the pod including the beans

becomes black in colour. If the infection occurs in the early stages

of pod development, the beans may not develop fully and get

mummified.

Charcoal pod rot

Fungus: Botryodiplodia theobromae [Diplodia theobromae]

Pycnidia are upto 5mm in dia. Conidiogenous cells are 5 to 15 µm.

Conidia are hyaline and thin walled, becoming thick walled, dark

brown and single septate.

Spraying with Bordeaux mixture 1.0 per cent is recommended for

controlling this disease.

Since injury on the pods caused by insect attack is a predisposing

factor, a combination spray is given by mixing with insecticide.

Rodent control is also necessary to reduce the disease.

Management:

Witches’ broom disease:

Infection of buds results in systemic infection of young shoots which

stimulates the growth of lateral buds in the leaf axils to produce the

broom effect - a cluster of closely formed stems.

Diseased stems are thicker. Only few leaves are produced. The

brooms dies after several weeks but remain attached to the tree.

During wet weather small, pinkish mushroom - like fruiting bodies

are produced on dead brooms.

The fungus infects flower cushions and produce parthenocarpids

and floral brooms. Pods are infected at an early stage and they are

distorted. The internal tissues are destroyed. External necrosis of

fruits occur just before ripening.

Symptoms:

Marasmius perniciosus

Mode of spread and survival: Basidiospores which cause

infection are released during night and they are spread through

wind.

Management: Young brooms before the production of sporophore

should be removed. Varieties like:

Scavina 6 and hybrids of this variety are resistant.

It was first reported in cocoa from Ghana by Posnette (1940). In 1936, peculiarly swellings on cocoa branches were noticed in the eastern region of Ghana and the phenomenon named swollen shoot.

Swollen shoot

•Swellings develop on nodes, internodes and tips of the quick growing shoots. Swellings on tap root is noticed. Necrosis may be observed on fibre roots.

•Red vein banding appears in the early stages and produce a network over the lamina. Later, the pigment is restricted to the midrib and lateral veins and portions of the finer veins adjacent to them and produce the 'red feathering' stage. Reddening usually disappears as the leaves turn green and harden. It may change to a green vein banding which sometimes temporarily retains a reddish tint. As the leaf enlarges, the red pattern is joined by chlorotic or transparent lesions. It is usually associated with the veins. Later, chlorosis takes the form of blotching or spotting and coalesce into bands or blocks. These patterns, unlike reddening, disappear as the leaf matures, but may undergo changes until hardening has reached the final stage. They seem to result from disorder of the tissues, preventing it from developing properly. The mesophyll remains undifferentiated, lacking intercellullar spaces. The chloroplasts remain small and flattened.

Symptoms:

•Young unripe pods develop a light and dark green mottling.

Then this is overlaid by dark marbling or blotching.

The surface of the pods becomes smoother and its shape

rounder.

Infected plants gradually die-back beginning with the drying up of

twig tips. Though fruit production is slightly reduced in the year of

infection, significant yield losses is noticed after a few years.

Causal agent: Cocoa swollen shoot virus (CSSV), Theobroma

virus- 1 or Cocoa mottle leaf virus. The virus particles are

bacilliform, not enveloped and 28 x 130 nm in size. The thermal

inactivation point of the virus is 55 to 60°C, longevity in vitro is 28

to 85 days.

Mode of spread and survival:

The virus spreads systemically throughout the plant. It is transmitted by insect vectors, especially mealy bugs or mechanically or by grafting.

Main vectors(mealy bug) are Dysmicoccus brevipes, Ferrisia virgata, Planococcus celtis, P. citri, P. kenyae, Pseudococcus longispinus. Transmitted in a semi-persistent manner.

Passively they are transmitted by wind, harvested fruit or planting material and ants.

Remove and burn infected parts and severely infected plants.

In addition, all wild plants serving as host for the virus or vectors like

wild Theobroma, Adansonia digitata, Cola chlamydantha, Cola

cordifolia,

Hibiscus spp., should be eradicated within and near cocoa plantation.

In old cocoa plantations, the control of the mealy bug vectors with

contact insecticides is difficult because the insects find a number of

hiding places and are protected by ants so that the chemicals do not

reach them. Removal of all dead twigs and ant nests especially in

younger plantations, control of the protectants, i.e. the ants, with DDT,

aldrin and dieldrin and direct control of the mealy bug vector with

parathion and systemic insecticides in young plantations have been

proved successful. Proper spacing of individual trees within plantations

helps to reduce the spread of the pathogen by vector.

Management:

A large number of insects feed on cocoa. The adaptation of local

insects takes 20-30 years when cocoa is introduced into any area.

However, although over 1500 different insects are recorded on

cocoa, only about 2 per cent has economic importance.

The occurrence of insect species is characteristic to countries. The

primary pests of cocoa are mirids (Capsids), pod borers and

bollworms. Others like mealy bugs are important as they act as

vectors of viruses. Another serious pests are the rodents, which

cause considerable loss to pods (Entwistle, 1985).

PESTS:

The most important mirids (Capsid) that attack cocoa are Helopeltis

antonii, Sahlebergella singularis, Distantiella theohroma and

Monalonion spp. These are found widespread in South America,

West Africa and Sri Lanka (Entwistle. 1972; Gibbs et al .. 1968).

Helopeltis is reported to infest in Indian states (Abraham and

Remamony, 1979; Daniel, 1994; Sundararaju and Babu, 1999).

Mirids feed by sucking the juices from plant tissues. The nymphs

and adults infect cherelles, pod stalks, chupons and fan branches.

This results in water soaked areas of tissue forming lesions, which

later turn black. The Helopeltis is especially severe in cherelles

causing wilting.

Mirids

Lindane has been used to control the pest.

A few parasitoids and many predators have been recorded, but

attempts for biological control have been unsuccessful.

The chemical control of mirids is not easy, as it requires high volume

spraying. The chlorinated hydrocarbons and gamma-HCH were used

earlier in West Africa to control mirids. Later low volume spraying

methods have been developed. However, if the pest attack is

limited, it is better to avoid any chemicals and allow biological

control to take place in nature.

Management:

The mealy bugs are small sap sucking insects characterized by

sedentary flightless, juvenile and adult female stages covered by wax

sections dorsally.

Population dynamics of mealy bugs vary among cocoa progenies and

variable susceptibility has been observed (Campbell, 1990).

Cocoa mealy bug, Planococcus lilacinus was reported to be a serious

pest in seventies in India (Radhakrishnan Nair, 1979).

Other mealy bugs recorded on cocoa are P. citri and P . Njalensis.

Ants for their sweet excretory substance generally attack these

mealy bugs. Mealy bugs cause damage to all parts of cocoa plants

especially the tender portions.

Mealy bugs

The control of mealy bugs has been found to be difficult. There are

three main approaches for effective control viz., biological control,

control of ants and pesticidal control.

Natural enemies of mealy bug like ladybird beetles and other

predators have been reported. But it has not given appreciable

control over the pests.

Use of pesticides to control mealy bugs indirectly by controlling ant

population is with high risk of persistence of pesticides and is

generally not recommended. Spraying of systemic insecticides was

effective in controlling the mealy bugs.

Management:

The most abundant species of thrip that attack cocoa is

Selenothrips rubrocinctus.

They infect lower leaf surfaces. The sap sucking results in leaf

shriveling. The population is found to increase with soil stress

conditions. The use of drought tolerant types can control the thrips.

However, chemical control with spray is also possible.

Thrips

The aphid species, Toxoptera alurantii that is dark brown to

black in colour, affects tender leaves, cushions and cherelles.

The other minor aphid found on young shoots and flowers is

Aphis gossypii.

The aphids are not considered as serious pests, but results in

leaf curling and flower wilt.

Aphids

Phassus hosei and P. sericeus are ring bark borers.

They damage the bark around the stem. They attack both young

and old trees.

Drenching 1 per cent dieldrin into the holes and sealing them can

control the pest.

Red borer: (Zeuzera coffeae ) have been recorded in several

countries (Daniel. 1994; Kalshoven, 1919b). These damage the

plants by making tunnels in the stem. The damage is considerable

and when young stems are attacked, the plants die. Control is

achieved by pruning affected branches and application of

insecticides.

Ring bark borers

Conopomorphs crameralla is a small moth which does much

damage to pods in Java and the Philippines. It also occurs in Papua

New Guinea and the Celebes.

Eggs are laid in the epidermis of pods, usually in furrows.

The larvae go through the husk and bore around the beans for l5-

18 days before leaving to form a cocoon.

Damage cannot be seen until the pod is opened and found to be

full of frass; the beans are useless.

Cocoa Moth (Cocoa Pod Borer)

The spiny bollworm of cotton, Earias biplaga, attacks cocoa from

Cote d'Ivoire to the Congo. It mainly attacks unshaded plants up to

3 years old.

It is therefore a greater problem on cocoa planted on clear-felled

land, particularly when the early shade is inadequate. They bore

into the pericarps of unripe pods.

The control can be achieved by providing adequate shade during early planting.

A systemic insecticide, such as monocrotophos, is recommended in someareas.

Bollworm

The longhorn beetle, Steirastoma breve, is a pest of cocoa in many

countries.

Eggs are laid in holes in the bark. The larvae bore a chamber in the

cambium and bark. From the chamber a tunnel is bored in a spiral,

which

often rings the stem so that it dies. A pupal chamber is then bored

in the

heart wood, weakening the stem. A gummy, gelatinous exudate

appears

around holes through the bark made by larvae. Trees from 6 months

to 5 years are attacked.

The intensity of attack increases as the amount of shade is

reduced.

Cocoa Beetle

Attack by Xyleborus beetles are of economic importance as they

also carry spores of fungal species of Ceratocystis. These beetles

cause characteristic small round holes in the trunk and branches.

Systemic insecticides like Endosulfon, Quinolphos, Dimethoate are

used to control the beetles.

Ambrosia Beetles

Several mammalian pests like rodents, squirrels and civets cause

damage to pods in all cocoa growing countries (Thorold, 1975).

In South India, squirrels and black rat (Rattus rattus) caused severe

damage to cocoa (Keshava Bhat et al., 1981).

The palm civet and bonnet monkeys caused minor damages. The

squirrels make holes in center or terminus of pods, while rats feed

near the stalk portion (Keshava Bhat, 1980).

For controlling squirrels live box traps were most effective (Keshava

Bhat and Mathew 1983). The anticoagulants like Warfarin and

Fumarin are effectively used to kill rats. These rodenticides (0.05%

brodifacum) have been effectively used in controlling rats in cocoa

gardens (Keshava Bhat and Sujatha, 1989; Smith and NOtt, 1988).

Vertebrates

References:

Diseases of Horticultural Crops- Dr. G. Arjunan, G. karthikeyan, Dr. D. Dinakaran, Dr. T. Raguchander

Plantation crops Volume 1 - V. A. Parthasarathy, p. K. Chattopadhyay, T. k. Bose

Coffee, Cocoa and Tea - K. C. Willson

Introduction to Spices, Plantation crops, Medicinal and Aromatic Plants

- N. Kumar, JBM Md. Abdul Khader, P. Rangaswami, I. Irulappan