This disease occurs in almost all the cotton growing countries of
the world. When humidity is high it assumes serious proportions.
Symptoms
Small, pale to brown, round or irregular spots measuring 0.5 - 3
mm in diameter and cracked centres appears on the affected leaves of
the plant.
Affected leaves become dry and fall off.
The disease may cause cankers on the stem.
The infection spreads to the bolls and finally fall off.
Epidemiology
High humidity, intermittent rains and moderate temperature are congenial
for the development of disease.
Disease Cycle
The undecomposed crop residues and infected seeds provide the primary
source of inoculum, giving rise to infected cotyledons, which support
the early stages of an epidemic.
Periods of high humidity encourage sporulation and infection spreads
from the cotyledons to the lower leaves.
Primary infection of lower canopy leaves can be initiated from conidia
splashed up from infected crop residues or blown into the crop from
other foci of infection.
Alternaria spp., also attacks the bolls and grow on exposed lint
if bolls open in wet weather, giving rise to contaminated seed.
The disease cycle is completed when infected leaves fall to the ground.
Control Measures
Sanitation
The plant residues should be removed from the field.
Carbendazim, Mancozeb 2.5gm, Copper Oxychloride 3gm in one litre
of water should be sprayed for 3-4 times in every 15 days gap.
The disease has been found in Bihar, U.P and Punjab.
It causes much damages when environmental conditions are favourable
for the growth of the plants.
Symptoms
The disease affects older leaves of mature plants.
The spots are round or irregular in shape yellowish brown, with purple,
dark brown or blackish borders and white centres.
Affected leaves become pale in colour and finally fall off.
Control Measures
Fungicides like carbendazim 3gm/litre, copper- oxy- chloride 3gm/litre,
Mancozeb 2.5 gm/litre, Captan 2 gm/litre, for 3 to 4 times in every
15 days gap should be used.
The disease is known to occur in United States, India etc.,
It occurs usually in low lying moist localities and minor importance
though in M.P becomes serious in wet years.
Symptoms
It usually appears on plants, which are coming to maturity.
Irregular, angular, pale translucent spots measuring 1-10mm (3-4mm)
in diameter and bordered by the veinlets, appear on the older leaves.
As infection starts, leaves become yellowish brown end finally fall
off prematurely.
Disease Cycle
The disease cycle spreads mainly through air - borne conidia.
The method of perpetuation during the off - season is unknown.
Epidemiology
It mainly develops in the moist localities and also low-lying wet
soils. When the temperature is 25-30°C the conidial germinate.
Control Measures
Destroy the infected-plant debris.
Avoid continous cultivation of cotton.
Spraying wettable sulphur 3g or Karathane 1g or benomyl 1g per litre
of water controls the disease. Spray 2-3 times at weekly interval till
it is controlled.
Originated from Mexico - Central America and spread to other
growing areas through the infected seeds.
Prevalent in black soils of Madhya Pradesh, Karnataka, South Gujarat,
Uttar Pradesh and the Punjab.
Wilt pathogen is rapidly destroyed in alluvial soils during the hot
months preceding the monsoons.
The disease is found in the areas where soil temperature during the
growing period of cotton ranges from 20º - 30ºC. This disease occurs
on all seasons.
Symptoms
Affects the host at all the stages of growth.
Earliest symptoms to appear on the seedling is the yellowing and
browning of the cotyledons.
In young and grown up plants the leaves loose their turgidity first
turn yellow and then brown and finally drop off.
The tap root of a wilted plant is usually stunted and laterals are
less abundant.
Browning and blackening of vascular tissues. (Outstanding diagnostic
symptoms)
Discoloration of woody tissues can be traced upon the surface of
the host as a black streaks.
Discolouration of leaves starts from the margins and spread towards
midribs.
Wilting may be complete or partial.
Epidemiology
Soil temperature and soil moisture greatly influence the incidence
of the disease.
The temperatures between 24-28ºC are optimum for attack on early stages
of crop.
Disease Cycle
The fungus enters the young host roots through the incidental wounds
and openings caused by insects and eel worms.
The fungus moves up through xylem vessels by the growth of the mycelium
and movement of spores.
The mycelium partially or completely plugs the xylem vessels and
stops or lowers the upward flow of water along the dissolved salts.
If the bolls are present, the mycelium may grow through peduncle
into the seed.
This results stunting and wilting of the plant.
Fungus survive in soil as a saprophytic plant.
Control Measures
Grow resistant varieties.
Provide good drainage.
Follow crop rotation 3-4 years once.
Treat the seeds with 4g Trichoderma viride formulation + thiram
3g/kg seed.
Destroy the infected - plant debris.
Apply 2kg of Trichoderma viride commercial formulation with
50kg farmyard manure along with the rows in the mainfield reduces
the disease incidence.
Cultural Methods
Mixed cropping of cotton with immune offers some protection to the
crop against the wilt.
Potash reduces wilt while nitrogen and Phosphorus increase it in
certain limits.
The disease occurs in irrigated and rainfed areas of Gujarat,
Punjab, Madhya Pradesh and Andhra Pradesh.
High soil temperature favours the development of the disease. June,
July are months in which diseases attacks severely.
This disease occurs on all seasons.
Symptoms
The sudden and complete wilting of the plant (first and the
most prominent symptoms).
Bronzing or yellowing of the leaves.
Plants succumbed to this disease exhibit roots particularly
the bark, broken down into shreds.
Affected plants occur in more or less circular area and can
be easily pulled out.
Except the tap root, few secondary roots are fresh which holds
the plant and other roots are decayed.
Tip of the root of a freshly wilted plant is slightly moist
and sticky.
Epidemiology
Plants suffer high mortality at soil temperatures > 39ºC.
Adequate supply of water, favours the development of disease when
the plant is in early growth.
Disease Cycle
The plants are vulnerable to infection the fungi dominate inside
the root.
The hyphae multiply rapidly in the cortical tissues and extend to
the pith and sometimes enter the xylem vessels.
There is an increased accumulation of calcium and iron in a diseased
plant roots and certain toxic substance play a role to wilt.
Fungus remain saprophytically on host root in soil.
Control Measures
Inter cropping of cotton with moth bean (vigna acomitifolia)
reduce the incidence. (moth bean helps in reducing the temperature
and retention of high soil moisture due to shading effect).
Chemical Control
Adjustment of time of sowing when soil temperature is not high.
Mixed cropping with Moth bean (Vigna aconitifolia) check the disease
intensity.
Seed treatment with benomyl or carbendazim @2.5g/kg seed reduces disease
incidence.
Apply 2kg of Trichoderma viride commercial formulation with 50kg farmyard
manure along with the rows in the main field reduces the disease incidence.
The disease has been found in Bombay, M.P, Andhra and Maharastra.
It reduces the photosynthetic activity of the plant.
The lint of the bolls may also get stained there by lowering its
market value.
It occurs in December and January.
Symptoms
The disease usually affects parenchymatous tissues and vascular bundles.
Four common symptoms are developed.
Angular leaf spots on the leaves (Water soaked leisions that are
angular in outlines)
Black arm lesions on the stem.
Boll rot and gummosis (Boll blight) round leisions, water soaked.
Seedling infections.
Leaf lesions appear as minute, water soaked spots on the under surface
of young leaves.
The disease on the stem and petioles appear in form of elongated
greyish to sooty black lesions which under favourable environmental
conditions.
The disease appears first as small, round, water - soaked, raised
spots. The lesions gradually became irregular in shape, turn brown to
deep black in colour and become in the center.
The disease first appears on the margins of the ventral side of the
cotyledons as small water soaked, circular or irregular but not angular
spots.
Epidemiology
The primary infection depends upon soil temperature and moisture.
The secondary spread of diseases should have the presence of moisture.
Disease Cycle
The primary infection is mainly through seed - borne bacteria.
Bacteria remain on the fuz of seed coat and multiplies after sowing
and infects the seedlings.
In case of seeds, bacteria may get inside the seed coat through the
micropyl to infect the seedlings.
The secondary, bacteria entering the host through natural openings
or insect caused wounds.
As the weather conditions favours, it multiplies and affect the growth
of the plant.
Control Measures
Sanitation
Removal and destruction of volunteer plants from the fields are very
essential, as they are the chief source of infection.
Cultural method
Crop rotation, late sowing, early thinning, good tillage,
early irrigation and addition of potash to the soil reduce the disease.
The seed is immersed in
sulphuric acid and should be arranged in wooden tubs or in earthen
jars.
Seed treatment with 2gms of carbendizam per kg of seed.
As it occurs in months of September and November, 100 mg of tetracycline,
streptomycin sulphate, plantamycin, poshamycin; should be sprayed for
3 or 4 times in every 15 days gap.
Chemicals linked with copper should be sprayed at their recommendation
of 3gm per litre of water to reduce the diseases.
Destroy the infected-plant debris.
Crop rotation, late sowing, early thinning, good tillage, early irrigation
and addition of potash to the soil minimise the disease.
Use healthy and resistant seed.
Acid delinting followed by seed dressing with carbendazim @3-4g/kg
of seed eliminates seed borne inoculum.
Foliar spray of combination of Pausha mycin/Plantomycin 100mg+3gms
of Copper Oxychloride per lit of water for 3 or 4 rounds at 15 days
interval from the time of disease appearance.
Detailed Study of Diseases
