Bud Rot Phytophthora
palmivora
Crown damaged palms |
- Palms of all ages are susceptible to the disease, but it is more frequent
on young palms.
- Yellowing of one or two young leaves surrounding the
spindle is the first symptom.
- The heartleaf becomes yellowish-green.
- Basal tissues of the leaf rot quickly and can be easily separated from
the crown.
- Infection spreads to the older leaves, causing sunken leaf
spots covering the entire leaf blade.
- Spot margins are irregular and
water-soaked, and when the leaves are unfolded the characteristic irregular spots
are conspicuous on the blade.
- In severely affected trees the entire crown
may rot and in a few months the trees wilt.
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Etiology - Fungus perpetuates on the host debris, in
crevices and natural openings of the dead tissue.
- With the onset of monsoon
rains and favourable temperature (18°-20° C), the fungus becomes active
and infects the tender host tissue. Control
Control
Budrot treatment | - Treated
wound should be given a protective covering till the next normal shoot emerges.
- Badly affected trees which are beyond recovery should be cut and burnt.
| - At initial stage of the disease when
the spindle is just withering, application of Bordeaux paste (100 g copper sulphate
and 100 g quick lime each dissolved in 500 ml of water separately and mixed together
to make one litre) on the crown after removing the infected tissue and a thorough
cleaning prevents the spread.
- All the healthy palms around diseased
plants should be sprayed with one percent Bordeaux mixture or copper oxychloride
(3 g/l).
Top Bacterial Leaf
Blight - Bacterial leaf blight is a serious disease of coconuts during
wet seasons.
Leaf blight affected leaf |
- The drying up of the leaves from the tip downwards, the progress of infection
being from the older leaves to the younger.
- The worst affected palms
present the appearance of severe drought-affected trees.
- The infected
leaflets may appear either at the base of the petiole or along the whole length
of the rachis.
- Diseased as well as healthy leaflets in many instances
appear intermingled on the rachis.
- Dark coloured lesions are found on
the back of the midribs of the affected leaflets.
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- They appear yellowish in colour, turning in course of time to a lighter
green water-soaked zone, which, while fresh, is quite transparent when held up
against light.
- On examination, almost transparent whitish bacteria are
seen lining the edge.
- In the most advanced stages, the diseased areas
become mottled in appearance and gradually become more pitted and stand out prominently,
especially near the edges of the diseased zone.
- Often confusion arises
between the bacterial blight and leaf spot (blight caused by Pestalotia palmarum).
- However, the lesions caused by P. palmarum are smaller and are more or
less with a regular margin.
- The dark pustules of Pestalotia infection
are absent in the bacterial disease.
Control
- Adopt the method of 'cutting and burning' the affected materials is considered
to be effective.
Top Fruit Rot: Phytophthora
omnivora - This disease is observed frequently in every country where
coconut is grown.
- Since the affected part is the fruit, its incidence
causes considerable loss in yield.
- There are no reported cases of the
palms being killed due to fruit-rot.
Fruit
Rot affected nut | - Rotting of the immature
nuts is the chief symptom of the disease.
- The affected nuts fall down.
- Near the stalks, a discoloured area is developed, which will appear at
first water-soaked and darker green than the rest of the surface of the nut.
- Later
on, the lesions turn brownish in colour and appear as depressions due to the decay
of the underlying tissues.
- The pathogen appears as a whitish matty growth
on the surface.
| - The rot extends into
the husk and often even into the endosperm cavity if the shell has not hardened.
Etiology - The causal organism has been
identified as Phytophthora omnivora.
- The infection takes place on very
tender tissues in the presence of moisture and in humid atmosphere; the pathogen
penetrates the fruit through the mesocarp and ramifies in that region.
- Consequently,
decay sets in those tissues of the host leading to the shedding of the nuts.
- The
pathogen is active during the rainy season and survives in the fruit stalk during
the dry weather, making itself manifest with the onset of favourable conditions.
Control - Fruit rot can be successfully
controlled by application of a copper fungicide, such as Bordeaux mixture, as
spray or paste, on the infected and wounded surface, preferably during the pre-monsoon
and post-monsoon periods.
- To be effective, the sprayings should be given
during the pre-monsoon and post-monsoon periods.
- In addition to spraying,
the crowns of the palms, whether affected or not, should be given a thorough cleaning.
- The shed nuts should be collected and burnt.
- Eradication of
the diseased materials and their destruction on the spot. Prophylactic spray application
of the fungicide on the apparently healthy neighbouring palms.
- Regular
cultural and manurial practices to maintain the palms in normal vigour.
Top Leaf Blight /Grey Leaf Spot
: Pestalotiopsis palmarum - Leaf blight is common in most of the
coconut growing states, particularly severe in Kerala.
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- Disease symptoms develop in the mature leaves of the outer whorl.
- They
appear at first as minute yellow spots encircled by a greyish band on the leaflets.
- It is characterized by the formation of greyish-white spots surrounded
by a brown band.
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Leaf
blight affected leaves | - These spots coalesce
into irregular necrotic patches. Gradually, the centre turns greyish white and
the brown band darken.
- Complete drying and shrivelling of the leaf blade
are common when the infection is severe.
| Control
- Removal of the older affected leaves and spraying the foliage with
1 per cent Bordeaux mixture will check the spread of the disease.
- Improving
drainage conditions, application of potassic fertilisers.
Top Leaf Rot : Bipolaris
halodes - Most prevalent in the Southern districts of Kerala.
Symptoms
Leaf
Rot affected seedling |
Symptoms on newly formed leaves |
- Symptoms first appear as blackening and shrivelling of the distal ends of
the leaflets in the central spindle and also in some of the younger leaves
Blackening and Shrivelling of leaflets |
- Later the affected portion breaks off in bits giving the infected leaves
a fan-like appearance.
- Each new leaf of the diseased tree gets infected
and all the leaves of the tree show disease symptoms.
- The reduction in
leaf surface adversely affects the yield.
| Control
- Spraying the leaves sequentially with 1% Bordeaux mixture, mancozeb
3g and Fytolan 5g/litre of water, at quarterly intervals after removing all severely
affected leaves reduces further incidences of the disease to a considerable extent.
Top Little Leaf Or Pencil Point
Disease - This disease is manifested by palms growing under unsuitable
environment or is usually a symptom of ageing.
- The characteristic symptom
of the disease is the steady dwindling of the girth at the top of the trunk that
gradually tapers to a pencil point.
- The crown at the same time gets reduced
both in number and size of the leaves.
- The axillary inflorescence do
not develop properly in advanced cases.
- When this condition is reached,
it is not possible to restore the palm to normal condition by cultural or manurial
treatments.
- In the early stages of the disease, proper attention should
be paid to plantation management, especially in rectifying deficiency of plant
nutrients.
Top Mahali Or Fruit-Rot And Nut-Fall This
is caused by the fungus Phytophthora palmivora. < Symptoms
- Dropping of the buttons, before and after fertilisation and of young and nearly
mature nuts in large numbers is the chief symptom of the disease.
- Near
the fruit stalks, a discoloured area is developed which will appear at first water-soaked
and darker green than the rest of the surface of the nut.
- In course of
time, these lesions turn brownish and appear as depressions due to the decay of
the underlying tissues. The fungus appears as a whitish matty growth on the surface.
- The rot extends into the husk and often into the kernel cavity especially
when the shell has not hardened. At times the axis of the inflorescence gets affected.
- The disease is usually prevalent in coconut palms growing in association
with areca palm.
- It is usually virulent after the rains of the S.W monsoon
when the atmospheric humidity is high.
Control
- Fruit rot can be successfully controlled by spraying the bunches
with 1% Bordeaux mixture to be effective, the treatment should be given during
the pre-monsoon and post-monsoon periods.
- In addition to spraying, the
crowns of the palms whether affected or not, should be given a thorough cleaning.
- The shed nuts should also be collected then and there and burnt.
Top Stem Bleeding Occurrence
- Stem bleeding disease was first reported from Ceylon. Later on, it
was observed in India, the Philippines, Malaya, Andamans and in Trinidad.
Ooze from cracks of coconut stem |
- The characteristic symptom of the disease is the exudation of a dark
reddish brown fluid from cracks in the outer tissue usually found at the lower
portion of the trunk, about 2m to 3m, from the ground.
- The fluid turns
black in colour as it dries up on the bark.
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Large cavity in the diseased stem |
- The tissues beneath the bleeding patches become decayed and yellowish.
- The infection may occur anywhere on the trunk, but is rarely observed
on the soft portion immediately below the crown.
- The symptoms exhibited
by young trees are different from those described above.
- On young palms,
the spread of the disease is more rapid.
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Darkening
of affected stem | - The external patches do
not indicate the extent of the internal decay.
- A general rot of the soft
inner tissue takes place, leading to the formation of a cavity in the central
portion of the stem and an accumulation of a thin yellowish fluid.
- The
fluid gushes out when the cavity is opened.
- The decay when directed downwards
to the bole, leads to the tree becoming hollow without any external symptoms.
| Etiology - Spores
of the fungus Thielaviopsis were observed in the liquid which oozes out.
- The
same fungus was isolated from the discoloured tissue underlying the bleeding patches.
- The fungus was identified as T. ethaceticus which is identical to Thielaviopsis
paradoxa or Ceratostomella paradoxa, the perfect stage of the fungus.
- The
fungus being a wound parasite, makes its entry through growth cracks which normally
occur on the coconut stem.
Different types of
stem bleeding - As mentioned earlier, the bleeding observed on the
coconut stem may be due to several reasons and it might also be of different types.
- Three distinct types of bleeding have been recorded in Malaya
- The
common type of bleeding due to the decay of the soft tissues about five centimetres
thick, in which case, the bleeding takes place from all available cracks on the
bark,
- Bleeding through abandoned white-ant galleries, and
- Bleeding
from one single wound associated with a' New disease' recorded in Malaya.
- The
disease caused by Ganoderma lucidum is associated with bleeding of the stem.
- Bleeding
patches occur at the base of the trunk all round resulting in the slow death of
the outer tissue; it extends higher up on the trunk as the infection advances.
- Occurrence of the stem bleeding due to physiological causes:
- Occurring
on neglected gardens following heavy manuring and subsequent drought. In this
case bleeding patches are reddish brown and circular, extending to a diameter
of about seven centimetres and commencing from 0.5 m to 1 m from the base.
- The
patches spread spirally about half way up the stem, and,
- Bleeding due
to heavy rains following drought; in this group there are two types of bleeding
- (a) in ill-drained soils following floods which does not cause much
damage; and
- (b) on lands with fluctuating water table; the bleeding under
these circumstances is extremely severe, the patches almost reaching the crown
and often causing the ultimate death of the palms.
Control
- The disease can be controlled to a certain extent by carrying out
the following treatments.
- The infected tissues should be cut out with
a chisel.
- The inner affected tissues should be scooped out till no diseased
tissues remain behind and dressing the wound with tar or Bordeaux paste.
- Since
T. paradoxa is not considered a virulent pathogen, but a wound parasite, palms
growing under unfavourable conditions having a large number of growth cracks are
more susceptible to the disease as the growth cracks form the foci of fungal infection.
- Hence general improvement of the cultural conditions is indicated where
the disease is of common occurrence.
Top Tatipaka Disease: Phytoplasma Occurrence
- Disease first observed in Tatipaka village of East Godavari district
in Andhra Pradesh, and hence the name.
Symptoms
Tappering of stem | - Plants between
25-60 years age are most susceptible.
- Development of an abnormally large
crown with dark green inner leaves and higher yield is the precursor of disease
incidence.
- Subsequently the crown becomes smaller in size and stem begins
to taper.
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Improper
unfolding of leaflets | - The leaves give a
fascinated appearance due to improper unfolding of leaflets.
- Leaves bend
in the middle abnormally. Yellow spots appear on the leaves.
- Leaf number
is reduced.
- The affected tree produces smaller bunches with atrophied
barren nuts.
| Control
- Remove and destroy affected trees.
- Avoid using nuts from infected
tree for nursery and raise seedlings only in disease free gardens.
- Avoid
transport of seedlings from infected areas.
Top Ganoderma Root Rot
And Wilt / Basal Stem Rot : Ganoderma applanatum
Bracket
of Ganoderma |
Ganoderma Affected Tree |
Ganoderma Affected Dead tree |
Ooze coming from stem tissue |
- Wilt disease is common from November to June in some gardens in South India,
particularly Andhra Pradesh, Karnataka and Tamil Nadu.
- Weak trees are
mostly affected in which the fungus infects the roots and spreads upwards killing
the entire root system.
- Older leaves which start drooping and withering
remain suspended around the trunk for several months before they are shed.
- The
trees become barren due to the suppression of the inflorescence.
- The
diseased tree dies slowly and often the stem cracks, giving out a dark brown ooze.
- In advanced stages of the disease, the fungus produces the fruiting bodies
(brackets) along the sides of the basal trunk.
- The diseased tree dies
in about two years.
Etiology - Fungus
is soil-borne. Disease is more severe and spreads fast in light soils than in
black soils.
- Spread is also fast during drought years.
- Death
of the tree is faster if there is bark eating caterpillar infestation also.
Control - Difficult to control as the disease is soil-borne.
Preventive measures recommended for restricting
the spread of the disease are: - Destroying the infected palms along
with the boles and roots and preventing the spread of the fungus by digging isolation
trenches about 50 cm wide 1 m deep, two to three meters away from the diseased
palm and rabbing the trenches.
- Trenches dug for replanting should be
filled with clay, farm yard manure and 5 kg neem cake before planting coconut
plant.
- As the disease is severe in light soils, green manure crops like
sunhemp and sesbania should be grown and incorporated into the soil for moisture
retention and multiplication of antagonistic fungi.
- Deep ploughing or
digging which are likely to injure roots should be avoided.
- Circular
basins of 2 m radius should be made around each tree and irrigation given separately
for each tree to restrict the spread of the fungus from infected to healthy tree.
- Apply farm yard manure (200 kg) and neem cake (5-10 kg) for each tree
during June -July months of the year.
- Also apply 2 kg super phosphate
and 3 kg muriate of potash per each tree in two split doses, first in July and
the second in November.
- Avoid using nitrogenous and complex fertilizers.
- Apply 40 litres of 1 per cent Bordeaux mixture in the basin of each tree
yearly once during August -September months.
- Mix 6 ml of tridemorph in
25 ml of water and apply 3 or 4 times an year by root feeding technique, in early
stages of infection.
- To control bark eating caterpillar, mix chlorpyrphos
2 ml per litre of water and apply the bark eating caterpillar infested area with
a brush at 15 days interval.
- Application of finely powdered sulphur and
lime at the rate of 2 kg each per palm to the soil around and trees is found to
be beneficial.
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