Symptom

1. Seedling blight

• Small, water-soaked, circular or irregular lesions on the cotyledons.
• Infection spreads to stem through petiole and cause withering and death of seedlings.

2. Angular Leaf Spot

• Small, dark green, water soaked areas develop on lower surface of leaves.
• The spots become angular restricted by veins and veinlets and are visible on both the surface of leaves.
• Later they turn reddish brown colour and infection spreads to veins and veinlets.

3.Vein necrosis or Vein banding

• 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 leaves become crinkled and twisted inward and show withering.
• The infection also spreads from veins to petiole and cause blighting leading to defoliation.

4. Blackarm

• On the stem and fruiting branches, dark brown to black lesions are formed.
• 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.

5. Square rot or boll rot

• On the bolls, water soaked lesions appear and turn into dark black and sunken irregular spots.
• Infection slowly spreads to entire boll and shedding occurs.
• Infection on mature bolls lead to premature bursting.
• The bacterium spreads inside the boll and lint gets stained yellow because of bacterial ooze and loses its appearance and market value.
• The pathogen also infects the seed and causes reduction in size and viability of the seeds.

Survival and Mode of Spread

• 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 primary infection is through seed-borne bacterium.
• Secondary spread is through wind, windblown rain splash, irrigation water, insects and other implements.

Favourable Conditions

• Optimum soil temperature of 28˚C,
• High atmospheric temperature of 30-40˚C,
• Relative humidity of 85 per cent
• Poor tillage, late irrigation
• Potassium deficiency in soil.
• Rain followed by bright sunshine during the months of October and November.

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 Carboxin 37.5% + Thiram 37.5% WS @2.5 g/ kg
• Remove and destroy 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.
• Spray Streptomycin sulphate @ 100g +Copper oxychloride@500 g/acre