Alternaria brassicae: Dark Leaf Spot

• Symptoms: dark brown spots on leaves become larger lesions with yellow margins and necrosis.
• Conditions for infection: warm, wet.
• Occurrence: a major disease of oil seed rape with spread and damage to other brassicas in most years.

Albugo candida: White Blister

• Symptoms: white, chalky blister-like pustules causing leaf malformation.
• Conditions for infection: warm, wet.
• Occurrence: not often a problem on oil seed rape but becoming more damaging on other brassicas.

Mycosphaerella brassicicola: Ringspot

• Symptoms: small dark spots on leaves become larger lesions with concentric rings of growth and a definite margin.
• Conditions for infection: warm, humid.
• Occurrence: a minor pathogen of brassicas that has become more damaging in recent years especially in Cornwall and Lincolnshire.

Pyrenopeziza brassicae: Light Leaf Spot

• Symptoms: very diffuse white spots on leaves due to spore masses give way to light brown lesions.
• Conditions for infection: cold, wet.
• Occurrence: a major disease of oil seed rape but not often damaging on other brassicas.

Peronospora parasitica: Downy Mildew

• Symptoms: Upper surfaces of leaves have ill-defined irregular pale yellow areas, sometimes with necrosis. Sporulation is seen as areas of diffuse white sporangiophores.
• Conditions for infection: cool, humid.
• Occurrence: widespread with severe attacks on brassicas in certain years.

Erysiphe cruciferarum: Powdery Mildew

• Symptoms: diffuse powdery mycelium initially white turning to pale brown. Infected areas coalesce and leaves become mealy and dry.
• Conditions for infection: warm, humid.
• Occurrence: widespread with severe attacks on brassicas in certain years.

Phoma lingam: Stem Canker

• Symptoms: light brown papery lesions on leaves become dessicated and dotted with black pycnidia. Stems develop a dry rot and lodging occurs.
• Conditions for infection: warm, humid.
• Occurrence: a major disease of oil seed rape but not often damaging on other brassicas.

Botrytis squamosa: Onion Leaf Blight

• Symptoms: numerous yellow sunken lesions on leaves. Premature die-back of leaves.
• Conditions for infection: cool, wet.
• Occurrence: a major disease of bulb and salad onions in most years.

Peronospora destructor: Onion Downy Mildew

• Symptoms: violet/purple lesions with grey/brown sporulation.
• Conditions for infection: cool, humid.
• Occurrence: a major disease of leeks in some years.

Puccinia allii: Leek Rust

• Symptoms: numerous red/brown pustules.
• Conditions for infection: warm, humid.
• Occurrence: a major disease of leeks in most years.

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This page created and maintained by John Clarkson).
Content produced and edited by Roy Kennedy and John Clarkson.