BENGAL GRAM :: MAJOR DISEASE :: ASCOCHYTA BLIGHT

Ascochyta blight - Ascochyta rabiei
Symptoms
All above ground parts of the plant are infected. On leaf, the lesions are round or elongated, bearing irregularly depressed brown spot and surrounded by a brownish red margin. Similar spots may appear on the stem and pods. The spots on the stem and pods have pycnidia arranged in concentric circles as minute block dots.  When the lesions girdle the stem, the portion above the point of attack rapidly dies. If the main stem is girdles at the collar region, the whole plant dies.

Symptoms

Pathogen
The fungus produces hyaline to brown and septate mycelium. Pycnidia are spherical to sub-globose with a prominent ostiole. Pycnidiospores are hyaline, oval to oblong, straight or slightly curved and single celled, occasionally bicelled.
Favourable conditions

• High rainfall during flowering.
• Temperature of 20-25˚C.
• Relative humidity of 60%.

Disease cycle
The fungus survives in the infected plant debris as pycnidia. The pathogen is also externally and internally seed-borne. The primary spread is from seed-borne pycnidia and plant debris in the soil. The secondary spreads is mainly through air-borne pycnidiopores (conidia). Rain splash also helps in the spread of the disease.
Management

• Remove and destroy the infected plant debris in the field.
• Treat the seeds with Thiram 2g or Carbendazim 2 g or Thiram + Carbendazim (1:1 ratio) at 2 g/kg.
• Exposure of seed at 40-50˚C reduced the survival of A. rabiei by about 40-70 per cent.
• Spray with Carbendazim at 500 g/ha or Chlorothalonil 1kg/ha.
• Follow crop rotation with cereals.