White Rust (Crucifer)

White Rust of crucifers, also known as white blister, is a destructive plant disease caused by the specialized Oomycete pathogen *Albugo candida* (not a true fungus, but a water mold). It attacks wild and cultivated cruciferous crops in the Brassicaceae family, including mustard, radish, cabbage, and broccoli. The pathogen behaves as an obligate biotrophic parasite, causing systemic swelling and leaf blister symptoms that reduce crop yields, stunt growth, and ruin the marketability of edible leafy greens.

Identifying white rust is simple due to the characteristic chalk-white blisters (pustules) that appear on the undersides of leaves. These pustules contain powdery masses of sporangia that break through the leaf skin. The upper leaf surface opposite the blisters displays yellow spots. In systemic infections, flower stalks and stems become grossly swollen, twisted, and deformed—a symptom commonly referred to as 'staghead'.

The oomycete targets cultivated brassica crops and wild mustards.

The oomycete overwinters as thick-walled survival spores (oospores) in crop residue or soil, or as active mycelium in volunteer weeds. During cool, wet spring weather (10°C to 18°C), oospores germinate to release swimming zoospores that spread via water splash and wind. Organic control focuses on crop rotation, planting resistant cultivars, and applying organic copper sprays. Chemical options include foliar sprays of metalaxyl or mefenoxam. For brassica disease guides, check our Plant Disease Identifier Hub, or explore similar threat profiles like Downy Mildew, Cabbage Maggot, and Clubroot.