Diseases of Vegetable, Ornamental and Spice Crops (2+1)

LATE BLIGHT

Symptoms

• On leaves, it appears as pale, green, irregular spots on the tips and margins, which in moist weather enlarge rapidly with central tissue turning necrotic and dark brown or black.
• On the lower surface of the leaves, a white downy growth of the fungus appears around the dead areas, which is more prevalent in morning hours when climate is moist (Plate-1a).
• Brown streaks also develop along the stems.
• On tomato fruits, dark, olivaceous greasy appearing spots are formed, which gradually cover the entire fruit surface (Plate-1b).
• Finally rotting of leaves and fruit takes place.

Pathogen:

• The disease is caused by Phytophthora infestans (Mont.) de Bary.
• The pathogen, disease cycle and epidemiology is described in detail under potato diseases.
• In India on tomato, 3 races namely 1.3.4.7.11, 3.11 and 4.7 were identified when tested on R0 to R11 gene differentials of potato.
• Race 1.3.4.7.11 was occurring both on potato and tomato.

Management

• Follow crop rotation and avoid solanaceous crops like potato in rotation.
• Improve drainage of the field and keep field free from weeds.
• Collect and destroy the infected fruits regularly.
• Before the initiation of the disease, apply one protective spray of mancozeb (0.25%) followed by metalaxyl + mancozeb (0.25%) at critical stage of disease appearance and repeat the sprays at 7-10 days interval.