Transcript foliar diseases

Foliar diseases
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Introduction:
 Foliar diseases are the diseases that infect foliar/ leaf part of the plant.
 There are so many numbers of foliar diseases. E.g. leaf spot, leaf blight,
anthracnose, powdery mildew, downy mildew, sooty mould and rust etc.,
since these diseases affect the foliar part, the photosynthetic efficiency of the
plant get reduced, ultimately the yield get reduced.
 The pathogen may be fungal, bacterial or viral diseases.
 The inoculums may have superficial growth (e.g. sooty mould) or enter inside
the plant cells (e.g. rust, powdery mildew) or may enter systemically (e.g.
viral) and affect the whole plant.
 The inoculums from leaf surface may spread as airborne (e.g.podwery
mildew) or through contact (viral, TMV) or rain splashes (bacterial disease).
 To manage the foliar diseases, spraying of the contact insecticides are
recommended.
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Late blight:
Symptoms:
The disease first appears as
water soaked, light brown
lesions on the leaf blade.
If the climactic conditions are
favorable with humid and
cloudy weather, these lesions
spread fast over the entire
leaflet and petiole.
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Characteristic lesions are roundish
with concentric ring marking on the
margin, and generally involve the leaf
margin.
The lesions which are dirty brown in
the beginning soon turn black.
The severely diseased plants wilt
within a few days after the first
symptoms are seen on the leaves and
in the fields the disease spreads like
wild fire, causing severe damage to
the crop yield.
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Leaf blight:
Symptoms:
On the leaves, spots of varying size appear.
The spots are irregular, brown to
dark brown in color, and have
concentric lines inside the spots.
Often several spots coalesce to
form large patches, resulting in
the leaf blight.
Fungicidal sprays, preferably with
copper fungicides or zineb given at
15 day interval effectively control the
disease.
In severe cases the entire
foliage is blighted.
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Control:
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Powdery mildew:
A grayish white powdery
growth occurs on the leaf.
Such symptoms also occur
on leaf sheath and floral
parts.
With the advancement of the disease, the powdery
growth may become dark grey and finally black, causing
characteristic lesions of varying size on the affected parts,
on which minute dark perithecia are seen.
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Control:
 While dusting the plants with fine sulphur would reduce the infection, it
is expensive and not practical.
 Use of one per cent sodium thiosulphate as a foliar spray has been
reported to give effective in checking the disease.
Mode of spread:
Warm humid weather and cool nights favor the spread of the pathogen.
Control:
 The disease is controlled with two preventive sprays of wettable
sulphur, once before the flowers open and a second time after the fruit
set.
 Two to three dusting with fine sulphur powder also check the disease.
 Spraying with sulfex (0.2 per cent) or wltasul (0.2 per cent) at
fortnightly interval.
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Rust:
Symptoms:
 The fungus produces characteristic
rust pustules on the hosts.
 The pustules are mostly found on the
leaf blade, though often they are
found on the petiole and stem of the
hosts.
 The sori are small, roundish, open,
powdery and brown colored.
 In severe infections the leaf withers,
resulting in considerable damage to
the crop.
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Control:
Growing short or long duration crops for such purposes is
also useful, and the application of balanced fertilizers to
the crop reduces the severity of infection.
Sulphur dust of 400 mesh fineness when applied
at the rate of 15 kg per hectare at weekly interval,
gives effective control.
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B. Red rust
Symptoms:
 The alga appears in the form of
minute rusty spots on the leaves.
 These spots enlarge, spread and
often become roundish, increasing to
about 10 to 15 mm in diameter.
 The spots are characteristically
reddish and hairy, occurring often on
the upper leaf surface, and spreading
to the stem.
 It is usually epiphytic on the leaves
and may also become parasitic.
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 When the leaves are severely infected, they are discolored and if
the stem is infected the shoots become pale so as to appear
unhealthy even from a distance.
 The disease is more or less chronic, as the alga can survive in the
stem and old leaves and becomes severe when bright sunlight is
available and also when new flush comes out.
Control:
Removal of the infected branches.
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Leaf spot:
Cercospora spp.
Symptoms:
 Usually water soaked lesions
appear on the leaf blade and
soon the affected tissues turn
brown to reddish brown.
 Well defined spots often
bound by veins and purplish Control:
border develop, the centers of
The leaf spots usually are controlled by
which may turn grey.
spraying with Mnancozeb or other
fungicidal sprays, at 15 days intervals,
starting from about a month after sowing
and up to fruit set, depending upon the
climactic conditions.
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Sooty mould:
Symptoms:
The honey dew secreted by
the insects on the leaves and
twigs of host plants attracts
the fungus, which multiplies
rapidly, spreading on the plant
surface.
Because of the production of
masses of black spores,
which stick to the leaf surface
the sticky honey dew, the
foliage appears black and
ugly and hence the name ,
sooty mould.
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Control:
Plants may be cleared of sooty mould by
spraying with diazinon or dimecron (0.03
per cent) to kill the insects, followed by
spraying with a starch solution, which dries
up and come off in flakes, removing the
sooty mould growth as it falls away.
Another spray with dimecron would help
eradicate the insects, thereby avoiding
another attack by the fungus.
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Bacterial leaf spot
Symptoms:
Control:
Agrimycin -100 and bavistin (0.1
per cent) control the disease.
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The disease first becomes
apparent
through
the
minute
water
soaked
lesions, bound the veins,
towards the leaf tip. As the
disease advances, the
lesions appear in groups
and are dark brown,
surrounded by chlorotic
haloes.
With age, the lesions
become necrotic and dry
up in patches.
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Mosaic disease
Symptoms:
The affected leaves shows mosaic
mottling in the beginning, after
which the young leaves show
severe
symptoms,
such
as
distortion
of
leaf
blade,
malformation and puckering.
The entire plant becomes stunted
and can be recognized from a long
distance.
Control:
Removal of the infected plants.
The spread of the insect vector may be
checked by spraying an effective
insecticide.
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YelloAw vein mosaic virus:
Symptoms:
The disease characterized by
yellowing of the entire net work
of veins in the leaf blade.
In severe infections, the young
leaves turn yellow, become
reduced in size and the plant is
highly stunted.
The damage caused may be
anywhere from 50-100 per cent
of yield.
Control:
Removal of the infected plant.
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Leaf curl virus:
Symptoms:
Puckering and severe curling of the
leaves,
together
with
mottling,
excessive branching and stunting and
complete sterility of the plant
Control:
Sprays insecticide with roger
(0.1 per cent) at fortnightly
interval are effective.
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Mycoplasma disease:
Little leaf:
The most characterized symptom is the reduction in size of leaves.
As the disease progresses the new leaves produced become smaller and smaller
with result that in course of a month the leaves are considerably reduced.
Both the petiole and lamina are involved in the reduction, the leaves becoming
almost sessile.
The leaves become thin, soft, glabrous and pale green in color.
In some varieties the thorns disappear.
The growth of axillary buds including buds is stimulated and this is accompanied by
the shortening of internodes of the branches.
The plant presents a characteristic bushy appearance.In many affected plants there
is no trace of any floral parts being present but whenever found these are modified
into green structures.
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Foliar diseases are the diseases that
infect foliar/ leaf part of the plant.
The common foliar diseases are ,,Late
blight, Powdery mildew, downy mildew,
rust ,leaf spot, Mosaic disease, leaf
curl and Mycoplasma diseases.
To manage the foliar diseases, spraying of
the fungicides are recommended.
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