Yellow Vein Mosaic of Okra

Causal Organism: Bhendi yellow vein mosaic virus (BYVMV), transmitted by the whitefly (Bemisia tabaci).

Symptoms

• Yellowing of veins and veinlets, followed by complete yellowing of leaves.
• Green areas become chlorotic, giving a yellow mosaic appearance.
• Leaves may become smaller, crinkled, and malformed.
• Infected plants show stunted growth with reduced fruit size and yield.
• Fruits are often malformed and of poor quality.

Mode of Spread and Survival

• Transmitted by the whitefly vector (Bemisia tabaci).
• The virus is not seed-borne but is persistent in the vector.
• Whiteflies acquire the virus from infected plants and transmit it to healthy ones.
• The virus survives in alternative host plants like Hibiscus spp. and Croton spp.

Favourable Conditions

• Warm and humid weather, which favors the multiplication of whiteflies.
• Dense planting and poor field sanitation contribute to the spread.

Management

1. Cultural Practices:
   • Use resistant or tolerant varieties, such as Arka Anamika and Pusa Sawani.
   • Rogue out and destroy infected plants to reduce inoculum.
   • Maintain field sanitation by removing weed hosts of the virus and vector.
   • Practice crop rotation with non-host crops like cereals.
2. Chemical Control: Spray systemic insecticides to control whitefly populations, e.g., Imidacloprid (0.03%) or Thiamethoxam (0.05%). Apply neem-based insecticides to reduce vector incidence.
3. Integrated Pest Management (IPM): Use yellow sticky traps to monitor and control whiteflies. Introduce natural enemies of whiteflies, like Encarsia formosa. Avoid using insecticides that harm beneficial insects.

Resistant Varieties: Parbhani Kranti and Arka Anamika are known to have moderate resistance to Yellow Vein Mosaic Virus.

Cercospora Leaf Spot of Okra

Causal Organism: Cercospora abelmoschi

Symptoms

• Small, circular to irregular brown spots with a grayish center and dark brown margins on leaves.
• Spots may coalesce, leading to extensive blighting and premature defoliation.
• Severely infected leaves turn yellow and fall off.
• Reduced photosynthesis due to leaf drop affects plant growth and yield.

Mode of Spread and Survival

• The fungus is spread by wind, rain splash, and insects.
• It survives in infected crop debris and on seeds.
• High humidity and warm temperatures (25–30°C) favor the disease.

Favourable Conditions

• High humidity and prolonged leaf wetness.
• Dense planting and poor air circulation.
• Warm temperatures ranging from 25°C to 30°C.

Management

1. Cultural Practices:
   • Practice crop rotation with non-host crops (e.g., cereals).
   • Destroy crop debris after harvest to reduce the source of inoculum.
   • Ensure proper spacing and avoid overhead irrigation to reduce leaf wetness.
2. Chemical Control: Spray with fungicides such as: Mancozeb (0.2%), Carbendazim (0.1%), Chlorothalonil (0.2%) Repeat sprays at 10-15 day intervals, depending on weather conditions.
3. Resistant Varieties: Grow resistant or tolerant varieties if available in the region.

Integrated Disease Management (IDM)

• Combine cultural, chemical, and biological control methods for effective management.
• Use disease-free certified seeds.
• Monitor fields regularly for early detection and control.