📈 Diseases of Cotton

Cotton is highly vulnerable to bacterial and fungal diseases across seedling, vegetative, and boll stages. Timely diagnosis and integrated management are essential to protect lint yield and quality.

Bacterial Blight (Angular Leaf Spot)

Causal organism: Xanthomonas citri pv. malvacearum

Symptoms

• Seedling phase: Water-soaked spots on cotyledons → "black arm" on stem
• Leaf phase: Angular, water-soaked lesions limited by veins → turn brown to black
• Boll phase: Round, dark brown to black lesions → boll rot and lint staining

Favorable Conditions

• Temperature 25–30°C, high humidity (>80%), wind-driven rain
• Seed-borne inoculum is primary source

Management

• Resistant varieties (Bt cotton hybrids with bacterial blight resistance)
• Acid-delinted, disease-free certified seed
• Seed treatment with Streptocycline (100 ppm) + copper oxychloride
• Foliar spray of Streptocycline (100 ppm) + copper oxychloride (0.3%) at disease onset

Fusarium Wilt

Causal organism: Fusarium oxysporum f.sp. vasinfectum

Symptoms

• Yellowing and wilting of leaves, initially on one side of the plant
• Brown discoloration of vascular bundles (diagnostic — cut the stem)
• Progressive wilting → complete plant death
• More severe in acidic, sandy soils

Management

• Resistant varieties (most effective)
• Crop rotation with non-host crops (cereals) for 3+ years
• Soil application of Trichoderma viride (2.5 kg/ha with FYM)
• Avoid waterlogging; maintain soil pH above 6.0

Root Rot Complex

Causal organisms: Rhizoctonia solani, Macrophomina phaseolina

Symptoms

• Seedling damping off (pre- and post-emergence)
• Brownish-black lesions on stem base → rotting of roots
• Charcoal rot (Macrophomina) shows black sclerotia inside stem pith
• Plants show sudden wilting during dry spells after initial rains

Management

• Seed treatment with Carbendazim (2 g/kg) or Trichoderma viride (4 g/kg)
• Avoid moisture stress and ensure proper drainage
• Deep summer ploughing to expose sclerotia to solar heat

Grey Mildew (Areolate Mildew)

Causal organism: Ramularia areola

• Angular pale spots on lower leaf surface with white powdery growth
• Common in late season with heavy dew and moderate temperatures
• Spray Carbendazim (0.1%) or copper-based fungicides

Summary Cheat Sheet