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Diseases
Bunchy top disease
The disease is transmitted to the plant by the aphid vector Pentalonia nigronervosa
and dwarf bananas are very susceptible to this disease. Primary symptoms of the
disease are seen when infected suckers are planted. Such infected suckers put forth
narrow leaves, which are chlorotic and exhibit mosaic symptoms. The affected leaves
are britttle with their margins rolled upwards. Characteristic symptom of bunchy
top virus is the presence of interrupted dark green streaks along the secondary
veins of the lamina or the midrib of the petiole. The diseased plants remain stunted
and do not produce bunch of any commercial value.
Control
- Use insecticidal treatments recommended for insect vector control.
- Eradicate
disease affected plants.
- Use disease free suckers for planting. Karpooravally,
Kanchikela, Njalipoovan and Koompillakannan are less susceptible varieties.
Panama wilt (banana wilt) (Fusarium
oxysporum f. cubense)
This is a soil-borne fungal disease and gets entry in the plant body through roots.
It is most serious in poorly drained soil. Initial symptoms are yellowing of lower
leaves, including leaf blades and petioles. The leaves hang around the pseudostem
and wither. In the pseudostem of the diseased plant, yellowish to reddish streaks
are noted with intensification of colour towards the rhizome. Wilt is severe in
poor soils with continuous cropping of banana. Warm soil temperature, poor drainage,
light soils and high soil moisture are congenial for the spread of the disease.
Control
- Dip suckers of susceptible varieties in 2 g/litre carbendazim solution to prevent
spread of the disease.
- Drench the soil around affected clumps with 2 g/litre carbendazim
solution to prevent spread of disease.
- Remove and destroy affected clumps along
with corms.
- Apply lime @ 1 kg/pit and allow to weather. Varieties such as Palayankodan,
Robusta and Nendran are resistant to the disease.
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Sigatoka leaf spot
(Mycosphaerella sp.)
Yellow sigatoka is one of the serious diseases affecting the banana crop. Initial
symptoms appear in the form of light yellowish spots on the leaves. A small number
of these enlarge, become oval; the colour also changes to dark brown. Still later,
the centre of the spot dies, turning light grey surrounded by a brown ring. In severe
cases, numerous spots coalesce, killing large parts of the leaf.
Rainfall, dew and temperature determine the spread of the disease. Conditions favouring
mass infection are most common during the rainy season with temperature above 21°C.
Control
- Cut and burn all severely affected leaves.
- Spray 1% Bordeaux mixture soon after the appearance of the initial symptoms of the
disease. The disease appears with the commencement of southwest monsoon. Five to
six sprayings at fortnightly intervals are to be given depending upon the severity
of the disease.
- Power oil (mineral oil) 1 g/litre emulsion is also effective in controlling
the disease.
- Spray carbendazim (0.05%) or give alternate sprays of mancozeb 2 g/litre and carbendazim 1 g/litre soon after the appearance of initial
symptoms of the disease. Three to four sprayings at fortnightly intervals are to
be given depending on the severity of disease.
- Spraying of cow’s urine (10%) /sucker
treatment with Pseudomonas fluorescens 5% + spraying 2% Pseudomonas fluorescens and
vegetable oil (2.5 ml/litre) +baking soda (2.5 g/litre)
Kokkan disease (Banana bract mosaic
virus)
Kokkan disease was first reported from Thrissur district in the variety Nendran.
Later on, the disease was found to affect other varieties like Palayankodan, Kodappanillakunnan,
Monthan, Kanchikela, Poovan (Rasthali), Karpooravally and Chenkadali. Nendran is
the highly susceptible variety.
During the young stage of Nendran banana plant (two months old), pinkish streaks
can be seen on the pseudostem. All the kokkan affected plants need not show this
symptom, but once this symptom is expressed there is no doubt that the particular
plant is affected with kokkan disease. Necrotic streaks are another important symptom
of the disease. The necrotic streaks are initially brown, which later turn black.
It occurs on all aerial parts of the affected plant except on lamina, the length
being a few mm to 10 cm. All the kokkan-affected plants will exhibit the necrotic
streaks from third month onwards at one stage or other. Some of the affected plants
retain the necrotic streaks throughout the growth period. In certain cases it disappears
with the senescence of the affected portion.
The affected plant produces only a small bunch. The fingers are small, curved and
widely divergent with pale green to ashy green colour as compared to the healthy
ones. The abnormal colour and reduction in the size of the bunch depend upon the
severity of the disease.
Control
- Suckers should not be taken from affected plants, which show necrotic streaks or
abnormal colour of the pseudostem.
- When the young plants show the symptom of
pinkish streaks, they should be uprooted and destroyed.
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Infectious chlorosis (Cucumber
mosaic virus disease)
The disease is noticed in varieties such as Nendran, Palayankodan, Karpooravally,
Kosthabontha, Peykunnan, Bhimkhel, Mottapoovan, Dakshinsagar, Madhuraga, Rasthali
and Musa ornata.
The most characteristic symptoms are the loss of leaf colour in patches; appearance
of parallel chlorotic streaks on the younger leaves, giving a striped appearance
on the leaves. As the disease progresses, leaves emerge distorted, margins become
irregularly wavy, often with blotches of necrotic tissues and the leaf lamina is
reduced in width. In severe cases, rotted areas are found throughout the leaf sheath
and pseudostem. The affected plants produce only small bunches. This is a virus
disease transmitted by aphids.
- Use disease free suckers for planting.
- Eradicate disease affected plants.
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Use insecticides recommended for insect vector control.
- Avoid growing leguminous
and cucurbitaceous vegetables as intercrop in banana in disease prone areas.
Banana streak disease
Banana streak disease is caused by banana streak badna
virus and transmitted by pineapple mealy bug (Dysmicoccus brevipes Cockerell)
and stripped mealy big (Ferrisia virigata Cockerell). It is predominant on palayamkodan
variety, also noticed on other varieties like Nendran, chinali, and mottapoovan.
The symptoms appear on different parts of the plant such as leaf lamina, midrib, pseudostem, and on bunches.
Linear chlorotic streaks appear on leaf lamina which later turned brown streaks.
Such dark brown linear lesion appear on petiole, midrib, pseudostem and bunches.
Under severe conditions, necrosis and death of cigar leaf is noticed and such plants
fail to flower and lead to total yield loss.
For the control of the disease, eradicate diseased plants, do not select
planting materials from infected clumps.
Avoid growing colocasia as intercrop and control of mealy bug vectors.
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