Cotton Diseases

Anthracnose
- Colletotrichum capsici
Symptoms
The pathogen infects the seedlings and produces small reddish circular spots on the cotyledons and
primary leaves. The lesions develop on the collar region, stem may be girdled, causing seedling to
wilt and die. In mature plants, the fungus attacks the stem, leading to stem splitting and shredding of
bark. The most common symptom is boll spotting. Small water soaked, circular, reddish brown
depressed spots appear on the bolls. The lint is stained to yellow or brown, becomes a solid brittle
mass of fibre. The infected bolls cease to grow and burst and dry up prematurely.

Pathogen
The pathogen forms large number of acervuli on the infected parts. The conidiophores are slightly
curved, short, and club shaped. The conidia are hyaline and falcate, borne single on the conidiophores.
Numerous black coloured and thick walled setae are also produced in acervulus.
Favourable Conditions
• Prolonged rainfall at the time of boll formation
• Close planting.
Disease Cycle
The pathogen survives as dormant mycelium in the seed or as conidia on the Surface of seeds for about
a year. The pathogen also perpetuates on the rotten bolls and other plant debris in the soil. The
secondary spread is by air-borne conidia. The pathogen also survives in the weed hosts
viz., Aristolachia bractiataand Hibiscus diversifolius.
Management
• Treat the delinted seeds with Carbendazim or Carboxin or Thiram or Captan at 2g/kg.
• Remove and burn the infected plant debris and bolls in the soil.
• Rogue out the weed hosts.
• Spray the crop at boll formation stage with Mancozeb 2kg or Copper oxychloride 2.5 kg or or
Carbendazim 500g/ha.
Wilt

- Fusarium oxysporum f.sp. vasinfectum

Symptoms
The disease affects the crop at all stages. The earliest symptoms appear on the seedlings in the
cotyledons which turn yellow and then brown. The base of petiole shows brown ring, followed by
wilting and drying of the seedlings. In young and grown up plants, the first symptom is yellowing of
edges of leaves and area around the veins i.e. discoloration starts from the margin and spreads
towards the midrib. The leaves loose their turgidity, gradually turn brown, droop and finally drop off.

Symptoms start from the older leaves at the base, followed by younger ones towards the top, finally
involving the branches and the whole plant. The defoliation or wilting may be complete leaving the stem
alone standing in the field. Sometimes partial wilting occurs; where in only one portion of the plant is
affected, the other remaining free. The taproot is usually stunted with less abundant laterals.

Fusarium oxysporum f.sp. Fusarium oxysporum f.sp. vasinfectum Fusarium oxysporum f.sp.
vasinfectum - Symptoms 1 - Symptoms 2 vasinfectum - Symptoms 3

Browning or blackening of vascular tissues is the other important symptom, black streaks or stripes may
be seen extending upwards to the branches and downwards to lateral roots. In severe cases,
discolouration may extend throughout the plant starting from roots extending to stem, leaves and even
bolls. In transverse section, discoloured ring is seen in the woody tissues of stem. The plants affected
later in the season are stunted with fewer bolls which are very small and open before they mature.

Pathogen
Macroconidia are 1 to 5 septate, hyaline, thin walled, falcate with tappering ends.
The microconidia are hyaline, thin walled, spherical or elliptical, single or two
celled. Chlamydospores are dark coloured and thick walled. The fungus also produces
a vivotoxin, Fusaric acid which is partially responsible for wilting of the plants.

Fusarium oxysporum f.sp.

Fusarium oxysporum f.sp. vasinfectum - Macro and
vasinfectum - Macro and
microconidia 1
microconidia 2
Favourable Conditions
• Soil temperature of 20-30˚C
• Hot and dry periods followed by rains
• Heavy black soils with an alkaline reaction
• Increased doses of nitrogen and phosphatic fertilizers
• Wounds caused by nematode (Meloidogyne incognita)and grubs of Ash weevil (Myllocerus
pustulatus).

Disease cycle
The fungus can survive in soil as saprophyte for many years and chlamydospores act as resting
spores. The pathogen is both externally and internally seed-borne. The primary infection is mainly
from dormant hyphae and chlamydospores in the soil. The secondary spread is through conidia and
chlamydospores which are disseminated by wind and irrigation water.

Management
• Treat the acid delinted seeds with Carboxin or Carbendazim at 2 g/kg.
• Remove and burn the infected plant debris in the soil after deep summer ploughing during June-
July.
• Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers.
• Apply heavy doses of farm yard manure or other organic manures. Follow mixed cropping with
non-host plants.
• Grow disease resistant varieties of G. hirsutum and G. barbadense like Varalakshmi, Vijay
Pratap, Jayadhar and Verum.
• Spot drench with Carbendazim 1g/litre.
Bacterial blight

- Xanthomonas axonopodis pv. malvacearum

Symptoms
The bacterium attacks all stages from seed to harvest. Usually five common phases of symptoms are
noticed.
i) Seedling blight:
Small, water-soaked, circular or irregular lesions develop on the cotyledons, later, the infection
spreads to stem through petiole and cause withering and death of seedlings.
ii) Angular leaf spot:
Small, dark green, water soaked areas develop on lower surface of leaves, enlarge gradually and
become angular when restricted by veins and veinlets and spots are visible on both the surface of
leaves. As the lesions become older, they turn to reddish brown colour and infection spreads to veins
and veinlets.
iii) Vein blight or vein necrosis or black vein:
The infection of veins cause blackening of the veins and veinlets, gives a typical ‘blighting’
appearance. On the lower surface of the leaf, bacterial oozes are formed as crusts or scales. The
affected leaves become crinkled and twisted inward and show withering. The infection also spreads
from veins to petiole and cause blighting leading to defoliation.
iv) Black arm:
On the stem and fruiting branches, dark brown to black lesions are formed, which may girdle the
stem and branches to cause premature drooping off of the leaves, cracking of stem and gummosis,
resulting in breaking of the stem and hang typically as dry black twig to give a characteristic “black
arm” symptom.
v) Square rot / Boll rot:
On the bolls, water soaked lesions appear and turn into dark black and sunken irregular spots. The
infection slowly spreads to entire boll and shedding occurs. The infection on mature bolls lead to
premature bursting. The bacterium spreads inside the boll and lint gets stained yellow because of
bacterial ooze and looses its appearance and market value. The pathogen also infects the seed and
causes reduction in size and viability of the seeds.
Pathogen
The bacterium is a short rod with a single polar flagellum. It is Gram negative, non-spore forming and
measures 1.0-1.2 X 0.7-0.9 µm.
Favorable Conditions
• Optimum soil temperature of 28˚C,
• High atmospheric temperature of 30-40˚C,
• Relative humidity of 85 per cent, early sowing,
• Delayed thinning,
• Poor tillage, late irrigation and
• Potassium deficiency in soil.
• Rain followed by bright sunshine during the months of October and November are highly
favorable.
Disease Cycle
The bacterium survives on infected, dried plant debris in soil for several years. The bacterium is also
seed-borne and remains in the form of slimy mass on the fuzz of seed coat. The bacterium also attacks
other hosts like Thumbergia thespesioides, Eriodendron anfructuosum and Jatropha curcus. The
primary infection starts mainly from the seed-borne bacterium. The secondary spread of the bacteria
may be through wind, wind blown rain splash, irrigation water, insects and other implements.
Management
• Delint the cotton seeds with concentrated sulphuric acid at 100ml/kg of seed. Treat the delinted
seeds with carboxin or oxycarboxin at 2 g/kg or soak the seeds in 1000 ppm Streptomycin
sulphate overnight.
• Remove and destory the infected plant debris. Rogue out the volunteer cotton plants and weed
hosts.
• Follow crop rotation with non-host crops.
• Early thinning and early earthing up with potash.
• Grow resistant varieties like Sujatha, 1412 and CRH 71.
• Spray with Streptomycin sulphate +Ttetracycline mixture 100g along with Copper
oxychloride at 1.25 Kg/ha.