Plant protection-Main Field
Pests
- Cardamom thrips( Sciothrips cardamomi )
- Borers
- Shoot/panicle/capsule borer[ Conogethes punctiferalis (Guen
. )
- Early capsule borer ( Jamides alecto
)
- Cardamom whitefly ( Kanakarajiella [Dialeurodes] cardamomi
)
- Root grub ( Basilepta fulvicorne )
- Hairy caterpillars
- Shoot fly ( Formosina
flavipes )
- Lacewing bug(Stephanitis typicus)
- Spotted red spider mites
- Nematodes
-
Rodents & birds
Diseases
- 'Katte' (Mosaic) disease
- Nilgiri necrosis
disease
- Kokke kandu disease (Cardamom vein clearing)
-
Azhukal or capsule rot disease
- Clump rot or rhizome
rot
- Minor diseases
- Chenthal
- Leaf blotch
- Leaf spots and leaf rusts
- Capsule canker and
capsule brown spots
- Leaf blight
1.Cardamom thrips
( Sciothrips cardamomi
)
|
Most destructive and persistent pest of cardamom.
They colonize and breed in different parts of the plant such as unopened
leaves, spindles, leaf sheaths, flower bracts, perianths and flower tubes.
Adults and nymphs of the insect cause damage to panicles, flowers and
capsules. It lacerates the surface tissues with mandibles and sucks the exuding
plant sap by applying its mouth cone.
Injury to panicles results in its stunted growth, that on flowers leads
to flower dropping and the injury produced on tender capsules develop as scabby
growth on capsules as they mature. Affected capsules appear malformed, shrivelled
and sometimes with gaping slits. Such capsules are inferior in aroma, have less
number of seeds, and seeds are underdeveloped and may not germinate.
Thrips affected capsules fetch very low price in the market. Thrips
infestation results in nearly 47% crop loss.
Adult insect is greyish brown, 1.25 to 1.5 mm long and with two pairs
of fringed wings. Adults lay minute kidney-shaped eggs, which hatch out into nymphs
in 12 days. Nymphs grow by feeding on plant sap and after passing through three
larval and a pupal stage become adults, thus completing their life cycle in 21-32
days.
Population of the pest is maximum in summer (February-May), minimum
in rainy period (June-July) and low in August-December.
Management:
1. Removal of collateral host plants of thrips, such as, Panicum longipes
, Amomum sp., Aframomum sp., Colocasia sp., Alocasia
sp., etc.
2. Remove dry drooping leaves, dry leaf sheaths, old panicles and other dry plant
parts immediately before the commencement of first application of insecticide.
3. Apply any one of the recommended insecticides at the specified time as given
below:
Insecticides recommended for thrips control (SP/EC formulations)
Insecticide
|
Strength (%)
|
Qty. (ml/g) of insecticide
per 100 litre water (High volume sprayer)
|
Quinalphos
|
0.025
|
100.0
|
Fenthion
|
0.05
|
62.5
|
Phosalone
|
0.07
|
200.0
|
Chlorpyrifos
|
0.05
|
250.0
|
Dimethoate
|
0.05
|
167.5
|
Acephate SP
|
0.075
|
100.0
|
4. During peak flowering periods, insecticide thart is less toxic
to honey bees (phosalone) may be sprayed.
5. If water scarcity is felt during summer months, any of the following
dust formulations may be applied.
Dust formulations
|
Chemical
|
Qty/ha
|
Methyl parathion
|
25 kg
|
Quinalphos
|
25 kg
|
Phenthoate
|
25 kg
|
Phosalone
|
25 kg
|
6. Recommended tentative schedule of insecticide application for
Kerala, Tamil Nadu and Karnataka is given below.
A. Kerala
|
1. February
2. March
3. April
4. May
|
Once in 30 days
|
5. August
6. September
7. October to November
|
Once in 40 days
|
B. Tamil Nadu
|
1. December to January
2. March to April
3. May to June
4. August to October
|
C. Karnataka
|
1. January
2. March
3. May
4. September to October
|
7. Evaluation of products against thrips revealed that Neemmark15G
and Nimbecidine were at par with monocrotophos in reducing the thrips damage
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2. Borers
2.
(a) Shoot/panicle/capsule borer
[ Conogethes punctiferalis (Guen .)]
|
Infestation of borers on shoot, panicle and capsule is a serious problem to cardamom
growers of Kerala, Tamil Nadu and Karnataka. The pest is larva of the lepidopteran
Conogethes ( Dichocrocis ) punctiferalis (Guen.). Adult
is a medium sized yellow moth with a number of black dots on its wings and abdomen.
After a pre-oviposition period of 3-4 days, the moths lay eggs mostly on leaves
or leaf axils of young pseudostem. After an incubation period of 5-6 days, the eggs
hatch. Emerging larvae bore into tender panicles or unopened leaf spindle or immature
capsule. At a later stage the larvae bore into the shoots. They feed the central
core of the pseudostem resulting in decaying of the central spindle and the characteristic
dead-heart symptom develops. When panicles and spikes are attacked, further production
of flowers on them is stopped and the portion ahead of the site of entry dries off.
In case of the capsules, the larvae feed on the seeds and the capsules become empty.
A fully-grown larva is 15-25 mm long with pale purple body and black head. Larval
period is completed within 28-36 days with five larval instars. After a pre-pupal
period of 2-4 days, it becomes pupa. After 11-15 days of pupal period, adult emerges
out through the borehole. The entire life cycle is completed within 41-51 days.
Management:
Pest infestation is pronounced in three seasons January to February, June, and September
to October. Late stages of the larvae bore into pseudostem and remain there. Insecticide
sprays at this time may not give adequate control of the pest. For an effective
management of the pest, the insecticide has to be targeted on early stages of the
larvae, which are usually present within 15-20 days after adult emergence in the
field. Injection of the insecticide solution through the borehole is the alternate
method for controlling larvae in pseudostem.
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2. (b) Early
capsule borer ( Jamides
alecto )
It is a serious pest of cardamom in Karnataka regions. Caterpillars of this insect
bore and feed flower buds, flowers and capsules. The attacked capsules are completely
emptied leaving a circular hole on the capsule, which eventually turn yellowish
brown, decay and drop off in rainy season. The pest incidence is high during June
to September.
Adult is a medium sized butterfly. Wings are bluish with metallic lusture on the
upper surface. Larval period lasts for 18-20 days. Each larva feeds on 25-27 capsules
to attain maturity. Pupation takes place in debris near the inflorescence. The life
cycle is completed within 3845 days.
Management:
Removal of old panicles at the last harvest.
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3. Cardamom whitefly
( Kanakarajiella [Dialeurodes]
cardamomi )
Whitefly was considered as a minor pest in the early eighties. Of late, infestation
of the pest has become severe and alarming in certain cardamom growing tracts of
Kerala. The adult is a small soft bodied insect about 2 mm long and having two pairs
of white wings. Adults are not active fliers, but can fly short distances. Female
lays eggs, which are inserted in to the leaf tissue. Eggs are cylindrical, pale
yellow when freshly laid and gradually turn brown. There are four nymphal stages.
The first instar larva crawls on the leaf and finds out a feeding site. It becomes
incapable of further movement from that place and all the later stages are completed
at that spot. The nymphs are elliptical and pale green. The nymphs secrete sticky
honeydew, which drops on to lower leaves. On these, black sooty mould develops,
which interrupts photosynthesis of the leaves. Puparia which adhere to the leaves
after emergence of adults appear as scaly patches on lower surface of affected leaves.
The life cycle is completed within 2-3 weeks depending on weather conditions.
Management:
The flies are attracted towards yellow colour. This behaviour can be exploited to
trap the flies on yellow sticky traps. Metal sheets painted yellow and coated with
sticky materials, such as castor oil or poly vinyl butanol would serve as sticky
traps. By placing such yellow sticky traps between rows of cardamom plants, population
of adults can be monitored and trapped to some extent. Nymphs are effectively controlled
by spraying on lower surface of leaves a mixture of neem oil (500 ml) and Triton
(500 ml) in 100 litres of water. Acephate 0.1% is effective. The spray may be
repeated two or three times at 15 days interval.
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4. Root grub (
Basilepta fulvicorne )
( Refer Pests in Nursery )
5. Hairy caterpillars
They are group of defoliators of cardamom and are polyphagous. Eight species of
hairy caterpillars have been found to damage cardamom plants. More destructive among
them are Eupterote undata , E. fabia , E. cardamomi ,
E. canairica, E. mollis and E. blanda . They occur sporadically
and congregate on trunks of shade trees. Moths emerge in June-July and lay about
300-800 eggs on the undersurface of leaves of shade trees. Eggs hatch in 15-25 days.
Larval stages extend up to three months and the pupal period for nearly three months.
When the north-eastern monsoon ceases, caterpillars drop down to cardamom and start
feeding on its leaves. Larvae make cocoons within which they pupate.
Management:
Larvae can be collected and destroyed. Since they congregate on tree trunks, mechanical
control is easy. If severe defoliation is noticed, spray chlorpyrifos 0.06%.
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6. Shoot fly (
Formosina flavipes )
( Refer Pests in Nursery )
7. Lacewing bug (Stephanitis
typicus)
It is a polyphagous pest, gregarious in habit. Nymphs and adults are found on lower
surface of leaves. They suck the cell sap from leaves, and later greyish yellow
spots develop on leaves. In case of severe infestation, plant growth is retarded
and yield is adversely affected. Adult is a small dull coloured bug with transparent
lacewings. A female lays about 30 eggs, which hatch in about 12 days. Nymphal period
lasts for 13 days. Damage is very severe in summer months.
Management:
Destruction of alternate host plants like banana, Colocasia sp. and spraying
of insecticides recommended for thrips control may be adopted for its management.
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8. Spotted red spider mites
(Refer Pests in Nursery )
9. Nematodes
(Refer Pests in Nursery )
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10.Rodents & birds
Damage by rodents and birds could be considerably minimised by adopting trapping,
clean cultivation, timely harvests and by baiting with bromodiolone (0.005%) or
Rodafarin cake
Bee and insecticide management in cardamom plantation
Cardamom flower is bisexual. The most conspicuous feature of the flower is the large
white labellum with violet streaks, which attracts insect for pollination. The essential
floral part – stigma, is placed at a higher level by a slender style. Anther
is situated well below the stigma. The flower thus represents a pin flower, which
is best adapted to cross-pollination by an insect pollinator. Flower opening in
cardamom is maximum between 5 a.m. and 7 a.m. Stigma receptivity and pollen viability
are maximum during morning hours.
The honeybees Apis cerana indica and Apis dorsata are the major
pollinators of cardamom flowers. Fruit setting increases significantly in bee-pollinated
flowers compared to flowers prevented from bee-pollination. Bees start foraging
in morning hours and it is high between 7 a.m. and 11 a.m. During misty days, the
forage is delayed for an hour or two. A bee usually visits all flowers in a clump
and crawl over the anther and stigma. During this process it carries anther from
one flower and a part of it gets deposited on the stigma of another flower. For
effective pollination in cardamom, four bee colonies per hectare are required. Studies
have indicated that an increase in yield up to nine per cent could be obtained by
keeping two to three bee boxes per ha of cardamom. Since bees are highly sensitive
to insecticides, certain precautions may be taken to prevent their destruction by
insecticides:
1. Dust formulation, which are more harmful to honey bees than
other formulations of insecticides, shall be applied only in times of acute water
shortage.
2. Insecticide sprays shall be done in afternoon.
3. Insecticides less toxic to bees may be selected for spraying
during peak flowering periods.
4. In the evening, previous to the day of insecticide application,
beehives may be closed and covered with wet gunny bags after providing sufficient
sugar solution and water in the hives. The hives may be opened on the next day morning.
Diseases
1. 'Katte' (Mosaic) disease
|
The disease is prevalent in all cardamom growing areas in India. It is one of the
major diseases of cardamom. 'Katte' disease affects plants of all ages. The first
visible symptom appear on the youngest leaf of affected tillers as spindle shaped
chlorotic flecks. Later, these flecks develop into slender discontinuous stripes
of pale green and dark green areas, running parallel to the veins from the midrib
of leaf margin. As the disease advances, subsequent leaves show characteristic mosaic
symptoms. The leaf sheaths and pseudostems also show mosaic pattern. Mature leaves
formed before infection do not develop symptoms. The infection is systemic in nature
and gradually spreads to all tillers of affected plant. Immediately after infection,
there is no growth reduction but within one to two years after infection, there
is a gradual reduction in clump size. In advanced stages, the affected plants produce
shorter and slender tillers with a few shorter panicles. 'Katte' affected plants
do not die but the plants give only poor yield. The yield reduction has been found
to be 70 per cent within three years after infection.
The disease is systemic and it is caused by cardamom mosaic virus. Viral particles
are present in all parts of affected plants except in mature seeds. The disease
is not transmitted through seeds or by mechanical means either by contact or through
cutting tools. The disease is transmitted by insect vectors. The common banana aphid
Pentalonia nigronervosa Coq. spreads katte disease from infected to healthy
plants by feeding. Even a single aphid can pick up and transmit the virus within
a few minutes without incubation period in the vector. All stages of the vector
viz., the nymphs, winged and non-winged forms of adults can transmit the disease.
Man acts as the main carrier of the disease over long distances by unknowingly transporting
the diseased materials for planting. Once the disease enters a plantation the spread
is internal through the vector. Disease incubation period (time required for symptom
expression) in the plant varies from 35 to 120 days in different months. Usually
during summer, delayed appearance of symptoms is noticed. Vector population is high
from December to May.
Management:
As long as katte inoculum is present in the field, any formulation of insecticides
fails to prevent the disease spread. Diseased plants cannot be cured but the losses
can be minimized by adopting the following measures:
a) Keep a constant surveillance on the occurrence of katte disease.
b) Use only healthy seedlings raised from 'katte' free plants.
c) Avoid rhizome planting using materials taken from disease-affectedsgardens.
d) Practise regular roguing (uproot and destroy).
e) Repeat tracing of affected plants and roguing at weekly intervals for at least
four consecutive months.
f) Replant the rogued areas with healthy disease free materials.
g) Destroy wild plants like Amomum, Alpinia, Curcuma, Colocasia etc. if
they show symptoms of katte.
h) Do not raise nursery near katte-affected areas.
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2. Nilgiri necrosis disease
It is also another viral disease like 'katte'. It was recently observed in Nilgiri
area and subsequently in Valparai in Anamalai, lower Pulneys and Munnar areas. As
compared to 'katte' it is of limited occurrence.
Diseased plants show alternate light green and whitish to yellowish streaks on the
leaves in the form of mosaic. Later these stripes become necrotic with reddish brown
colour followed by tearing of lamina. The leaves are crinkled with wavy margin.
The reddish brown necrotic areas later dry off. Tillers show reduction in height.
In advanced stages of infection, severe stunting of plants is seen. Tillers are
narrow, very short and they produce small leaves, which are brittle. Panicles become
shorter with few reduced capsules, which often show symptoms of cracking. In extreme
stages of disease no panicle is formed. The disease is caused by a rod shaped virus.
Like katte, it is a systemic disease. Nilgiri necrosis is not transmitted through
seed or mechanical means but the disease is easily carried through infected rhizomes.
So far, no insect vector is known to transmit the disease.
Management:
Plant sanitation by rouging of affected plants is the only method by which the disease
can be controlled. The methods adopted for the control of katte can also be followed
for managing Nilgiri necrosis disease.
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3. Kokke kandu disease
(Cardamom vein clearing)
Recently a new viral disease is found to be widely spreading in plantations of Karnataka
state. In Kannada, it is called 'Kokke kandu' which means hooked tiller. It is first
observed in Hongedehalla, which is the hot spot area of this disease. Later, it
spread to Sirsi and Somawarpet areas.
Diseased plants show symptoms on the tillers and leaves. Characteristic mottling
develops on the foliage which later show severe vein clearing. Yellow stripes or
streaks run parallel to the side veins. Leaves are arranged in a rosette manner
at the tip of the tiller with much reduced internodes. The tiller height is also
reduced. In advanced stages of infection, tillers are stunted and their tips form
hook like structures after the younger most leaf roll gets hooked up in the leaf
sheaths. Panicle length and number of capsules are much reduced. In extreme stages,
no panicles and capsules are produced and the yield loss is almost 100 per cent.
The disease spreads rapidly to nearby areas and the infected plants decline in a
short period of one to two years. No seed or sap transmission is noticed. The disease
spreads easily through infected rhizomes as in the case of katte disease. The banana
aphid Pentalonia nigronervosa is found to be its natural vector. It transmits
the disease in a non-persistant manner. There is no incubation period in the vector.
About 30 to 40 days are required for the infected plants to show the symptoms. Sometimes
combined transmission of 'katte' and 'kokke kandu' by the aphid is observed in the
same plant. The disease is caused by cardamom vein clearing virus.
Management:
As it is a systemic viral disease, infected plants can never be cured. Plant sanitation
is the only preventive measure. The methods recommended for katte control can be
followed for management of kokke kandu disease also.
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4. Azhukal or capsule
rot disease
'Azhukal' disease is mostly prevalent in Idukki and Wayanad districts of Kerala.
In recent years, it has been noticed in isolated pockets in Anamalai area also.
Azhukal (rotting) is caused by the fungus Phytophthora meadii
. The disease starts with the onset of southwest monsoon in June and becomes severe
during July-August months. It may continue to prevail up to November-December, if
weather is favourable for disease development.
Symptoms of rotting appear on all plant parts. First symptoms appear on the young
leaves or on capsules in the form of water soaked lesions. In leaves, these areas
enlarge, become necrotic and gradually the leaves shrivel and begin to shred. Finally,
the affected leaves break at the base of the petiole and remain hanging. Rot affects
the capsules of all ages. Affected immature capsules soon decay and fall off within
3 to 5 days and mature capsules get shrivelled on drying. Infection on the panicle
appears usually on panicle tip and proceeds downwards. Such portions later dry off
or decay if moisture is in excess. In severe cases, infection spreads over to the
rhizomes and tillers also. Decayed tillers break and fall off at the collar region.
All the varieties are susceptible to the disease. However, Malabar variety is more
severely affected due to this disease. The disease spreads through soil, water and
wind.
The predisposing factors favouring 'azhukal' incidence are heavy and continuous
rainfall, excess soil moisture, thick shade, overcrowding of plants and prevalence
of inoculum in the soil.
Management:
a) Phytosanitation
i) Trashing and cleaning the plant base are to be carried out during May before
the onset of monsoon.
ii) Thick shade may be regulated by gentle lopping of tree branches.
iii) Provide drainage in low-lying and marshy areas.
iv) Destroy the azhukal affected portions and plant debris.
b) Fungicidal applications:
After completing the above mentioned plant sanitation measures, the plants
may be sprayed with any one of the following fungicides.
i) Bordeaux mixture 1%
The first spray should be done during May-June before the onset of the monsoon and
a subsequent spray may be done during July-August. A third spray may be given in
the month of September if the monsoon is prolonged and disease is still persistent.
Spray Bordeaux mixture on the entire portion of the plants at the rate of 500 ml
to one litre per plant. Two to three litres of Bordeaux mixture drenching at the
plant base is to be done in areas where azhukal is severe. Alternatively, drenching
plant base with COC (0.25%) was found to be effective in reducing soil inoculum
and further disease spread. For easy percolation to deep soil layers, COC drenching
is found to be superior to Bordeaux mixture drenching.
Drench with Fosetyl –Al (3-5 l/plant) and repeat this at monthly interval
depending the intensity of the disease and rainfall.
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5. Clump rot or rhizome
rot
If is also a fungal disease occurring during the monsoon season. Symptoms of disease
are yellowing of leaves and decay of tillers starting from the collar region. The
decay extends to the rhizomes and roots also. Rotten rhizomes become soft, dark
brown coloured and ultimately result in the total death of the plant. Affected tillers
fall off by a slight disturbance. The disease is caused by soil-borne fungi such
as Pythium vexans , Rhizoctonia solani and Fusarium sp.
(in a few cases). In some cases, a pink colour develops at the collar region, which
later leads to rotting.
Management:
a) Plant sanitation as described in the case of azhukal disease
has to be followed to control this disease.
b) The plant base is to be drenched with 2-3 litres of COC (0.25%).
Repeat COC drenching at 30 days intervals for 2 to 3 times at monthly intervals.
As a boicontrol measure, inoculate suckers with native arbuscular mycorrhiza,
Trichoderma and Pseudomonas at the time of planting and apply
during pre-monsoon period in established plantations
General recommendations:
1. Plant protection measures are to be carried out on priority
basis.
2. Diseased areas should be taken first for trashing and spraying
with fungicides.
3. Spraying should be done covering the diseased portions.
4. When the plants are wet during raining, foliar spray may not
be effective. Practise soil drenching in such situations.
5. Top preference may be given for fungicidal sprays during non-rainy
days.
Biocontrol of rot diseases:
Recent studies show that azhukal and rhizome rot can be controlled to some extent
with the bio-agent Trichoderma . It is antagonistic soil fungus acting
against the rot pathogens. The fungus is green in colour and grows abundantly on
cowdung and organic crop residues such as coffee husk, tea waste, neem cake, coir
compost etc. Trichoderma viride or T. harzianum specific to cardamom
can be mass multiplied on carrier media for 30 to 45 days. These can be applied
to plant basins at the rate of 1 kg per 5 kg of cowdung during May, August, September
and October months after phytosanitation.
While Trichoderma is applied in the soil, no fungicide should be drenched
in the soil. However Bordeaux mixture can be sprayed before the application of Trichoderma
. If the soil is drenched with COC or other fungicides, Trichoderma
should be applied only after one month.
In severely diseased areas, first one or two rounds of fungicides can be applied.
One month after this, Trichoderma can be used. But never use fungicides
and Trichoderma together.
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Minor diseases
a. Chenthal
The disease is seen in almost all areas of cardamom cultivation. Initial symptoms
appear as water soaked lesions on young leaves. Later these become yellowish to
reddish brown with a pale yellow halo. In severe cases, it leads to the withering
of leaves and withering of psuedostems. The disease intensity is found to be severe
in open areas where shade is inadequate. 'Chenthal' was reported to be caused by
Corynebacterium sp. However, latest studies showed that it is not a bacterial
disease. It is caused by a fungus called Colletotrichum gloeosporioides.
Management:
Providing adequate shade is the only measure recommended pending confirmations of etiology of the disease.
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b. Leaf blotch
It is caused by the fungus Phaeodactylium venkatesanum. Symptoms develop as
dark brown blotches on the leaves during monsoon season. Later, on the under side
of these blotches, the fungal mycelium and spores develop as grey brown masses.
Management:
The disease can be controlled by one to three rounds of spraying with ,
carbendazim (1 g/litre) or Bordeaux mixture 1% or mancozeb (Dithane M-45) 0.3%.
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c. Leaf spots and leaf
rusts
Various types of leaf spots are found to affect the leaves. These are Sphaceloma
leaf spot caused by Sphaceloma cardamomi , Cercospora leaf
spot caused by Cercospora zingiberi and leaf rust caused by Phakospora
elettariae.
The Sphaceloma leaf spot is seen in main plantation as scattered spherical
blotches on the leaves. These start as small spots measuring a few mm and later
several spots coalese to form larger areas.
The Cercospora leaf spots are found in the nursery and plantations in the
form of rectangular muddy red stripes running along the veins.
Leaf rust is often seen on mature leaves as whitish powdery pustules on the under
surface of the leaves with corresponding yellow necrotic patches on the upper surface.
Diseased leaves show a rusty appearance.
Management:
The leaf spots can be reduced to some extent by spraying with fungicides such as
Dithane M-45 (0.25%) or bavistin (0.2%). For leaf rust, so far no effective fungicide
was found.
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d. Capsule canker and
capsule brown spots
Canker like symptoms and capsules were often observed as glazy discoloured erruptions
on the capsule rind. On curing, these spots turn greyish to dull white raised blisters
on the capsule surface. The etiology is not yet known.
The capsule brown spot, also called as anthracnose disease, is caused by the fungus
Colletotrichum gloeosporioides . Disease symptoms appear as small round
reddish brown lesions on the pericarp of the capsule. On maturation, these spots
become soft reddish sunken areas. On cured capsules also the spots retain their
red colour.
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e. Leaf blight
Leaf blight or drying of leaves in patches is observed during October to February
months. In areas covered by severe fog the severity is more. Brown dry areas of
varying sizes develop on the lamina. It is caused by Phytophthora meadii
.
Management:
It can be controlled by one or two rounds of spraying with 1% Bordeaux mixture or
0.3% aliette or 0.4% akomin.
One to two rounds of sprays with bavistin (0.2%) or Dithane M 45 (0.2%) reduces
further disease spread.
Preparation of Bordeaux mixture:
Dissolve 1 kg of copper sulphate in 10 litres of water.
In another vessel, slake 1 kg of quicklime by adding small quantity of water preferably
warm water (Up to 1.25 kg of lime can be taken if the lime is not of good quality).
When slaking is over, add 5 litres of water and stir well to get a uniform suspension
of lime. Transfer the lime suspension thus prepared through a sieve to a vessel
containing 85 litres of water and stir well. A small quantity of lime solution may
be kept separately.
Add 10 litres of the copper sulphate solution to the 90 litres of lime solution
with constant stirring. To test the correctness of the mixture, dip a brightened
iron knife for a minute in the mixture. If the knife remains bright, the mixture
is correctly prepared. If the knife turns rusty brown or if its brightness is lost,
add more lime suspension. Correctly prepared Bordeaux mixture will turn red litmus
to blue and turmeric powder to orange red in colour.
Important points:
1. For dissolving copper sulphate for Bordeaux mixture, use copper,
wooden, earthen or plastic containers.
2. Use fresh quicklime.
3. Bordeaux mixture should be passed through a sieve before transferring
to the sprayers.
4. Spraying of Bordeaux mixture should be done on the same day
of preparation.
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