Advice
RHS Help & Advice
White blister
Symptoms
White, blister-like pustules spread to cover the leaves, smaller stems and flowers. The pustules are frequently associated with swelling, distortion and abnormal pigmentation of the surrounding tissue.
Plants affected
Aubrieta, honesty, brassicas including cabbages, broccoli and Brussels sprouts, and other members of the cabbage family (Brassicaceae).
Members of the daisy family (Asteraceae) in particular salsify, but also cinerarias (Senecio cineraria and Pericallis x hybrida) and others, may also be attacked by a related species that does not attack crucifers. On these plants the disease is sometimes called white rust, but do not confuse this condition with chrysanthemum white rust, which is caused by a different fungus.
Cause
This fungal disease flourishes in damp conditions, and infective spores are dislodged from the pustules and dispersed by air currents, rain splash or by insects. It takes only short periods of dewfall for the disease to spread. Resting spores may also be produced and remain dormant in the soil or on plant debris for several months.
Non-chemical control
- Remove and dispose of infected leaves and other plant material.
- Clear up and dispose of plant debris.
- Burn or bin infected material, do not add to the compost heap.
- Plant resistant brassicas such as Brussels sprouts ‘Bridge’ F1, ‘Maximus’ F1 and ‘Exodus’ F1 (both field-tolerant cultivars) and field-tolerant broccoli ‘Green Magic’.
Chemical control
None is available to home gardeners.