2. KITTUR RANI CHANNAMMA COLLEGE OF HORTICULTURE, ARABHAVI
Chandalinga
UHS11PGM139

3. Diseases

4. 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.

5. 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.

6. 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.

7. White thread blight
Symptoms:
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.

9. 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.

10. Black pod disease
Symptoms:
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

13. Mode of spread and survival:
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.
Epidemiology:
The fungus infects chillies, citrus, coconut, cotton and rubber.

14. Epidemiology:
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.

15. Management:
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.

16. Charcoal pod rot
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.

18. 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.
Management:
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.

19. Witches’ broom disease: Marasmius perniciosus
Symptoms:
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.

22. 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.

23. Swollen shoot
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.

24. Symptoms:
•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.

25. • 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.

26. 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.

27. Management:
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.

28. PESTS:
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).

29. Mirids
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.

32. Management:
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.

33. Mealy bugs
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.

34. Management:
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.

35. Thrips
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.

36. Aphids
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.

37. Ring bark borers
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.

38. Cocoa Moth (Cocoa Pod Borer)
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.

42. Bollworm
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 some
areas.

43. Cocoa Beetle
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.

44. Ambrosia Beetles
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.

45. Vertebrates
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).

49. 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