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Agricultural crops :: Cereals :: Maize

Downy mildew : Peranosclerospora sorghi

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

Crazytop downy mildew : Sclerophthoram macrospora

Symptoms

  • 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 24-26o 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

 
 

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