Symptoms:

Symptoms

• Systemic infection as chlorosis which appears 10-14 days .
• Leaves tend to be narrower and more erect.
• Plants infected early usually die at four weeks after infection.
• Chlorosis is noticeable on the lower half of the leaf : Half-leaf symptom
• Chlorosis gradually covers the entire leaf surface at later stage
• A white downy growth is seen on the lower leaf surface under humid warm conditions
• Systemically infected plants do not form cob and if it forms they are small and poorly filled

Sorghum Downy Mildew in maize : Leaf Symtoms and condiaphore & conidia

• Leaves are narrow, strap like and leathery.
• Stunting and chlorotic striping of leaves .
• Excessive tillering and rolling and twisting of upper leaves
• Partial or complete changes normal floral parts to small leaves: crazy top
• Plants may produce numerous ear shoots and phyllody of ears.

Pathogen :

• Mycelium - non-septate, inter cellular, systemic and obligate
• Conidiophores are erect, fragile, hyaline usually dichotomously branched
• Sporangia germinate directly and infect the plants
• Oospores are spherical, thick walled and deep brown

Mode of spread :

• Primary spread through oospores in soil and seed-borne .
• Secondary spread by conidia / sporangia

Favourable Conditions :

• Temperature ranging from 24-26 o C.
• Continuous drizzling / rainfall.
• Relative humidity more than 80 %

Management:

• Use disease free healthy seeds.
• Drying seed to less than 14% moisture .
• Deep tillage and crop rotations for more than three years
• Roguing of diseased plants and alternate grass hosts
• Use disease resistance hybrids viz., TNAU COH(M)6, COH(M)8 and COH(M)11
• Seed treatment with metalaxyl @ 6g/kg of seeds
• Foliar spray with metalaxyl + mancozeb @ 1000 g or mancozeb 1000 g/ha after initial symptom / 20 DAP and 40 DAP

Chlorotic streaks on leaves