SORGHUM :: MAJOR DISEASE :: RECTANGULAR LEAF SPOT

Rectangular Leaf spot - Cercospora sorghi
Symptoms
The symptoms appear as small leaf spots which enlarge to become rectangular lesions (which can be 5-15 mm long by 2 to 5 mm wide) on the leaf and leaf sheath. Usually the lower leaves are first attacked. The lesions are typical dark red to purplish with lighter centers. The lesions are mostly isolated and limited by veins. The colour of the spots varies from red, purple, brown or dark depending upon the variety.
Pathogen
Mycelium of the fungus is hyaline and septate. Conidiophores emerge in clusters through stomata, which are brown and simple, rarely branched. Conidia are hyaline, thin walled, 2-13 celled and long obclavate.
Favourable Conditions

• Cool moist weather.
• High humidity (90 per cent)
• High rainfall.

Disease cycle
The conidia survive up to 5 months. The disease spreads through air-borne and seed-borne conidia.
Management

• Use disease free seeds.
• Treat the seed with Captan or Thiram at 4 g/kg.
• Spray Mancozeb 2 kg /ha.