PATH 372 Diseases of Horticultural Crops

2) Downy Mildew – Peronospora parasitica
Severe in raddish, cabbage, cauliflower, mustard, and knol-khol.
Symptoms
Small purplish brown spots on under surface of leaves
Small, pale yellow angular spots on upper surface of leaves, with downy growth on
the under surface.
The spots coalesce and the leaves shrivel and dries up prematurely
In cabbage, these spots expose the heads to soft rot
Cauliflower curds look brownish at the top
Stems show dark brown and depressed lesions or streaks which later develop
downy growth of fungus
Disease cycle
P.I: Oospores in infected plant parts or in soil
S.I: Wind borne sporangia
Management
Destruction of infected plant debris
Avoidance of thick sowing and excessive moist conditions
Spray metalaxyl@0.25% or COC@ 0.3% or Mancozeb@ 0.2% at 10 days interval
3) Powdery mildew – Erysiphe polygoni
Symptoms
Seen on cabbage & cauliflower
Symptoms
White powdery spots on the upper surface of leaves, stems, flower parts etc.
Finally the mildew may cover the entire surface.
Disease cycle
P.I: Mycelium in infected plant debris
S.I: Wind borne conidia.
Management: Application of Dinocap@0.2%
4) Alternaria leaf spot: Alternaria brassicola, A.brassicae, A.raphani
Common on cabbage, cauliflower and mustard.
Symptoms
Spots are small, dark coloured
They enlarge, soon become circular & 1mm. in diameter
Under humid conditions groups of conidiophores will be formed in the spot
Spots develop concentric rings
Finally the spots coalesce leading to blighting of leaves.
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