White Blister
White blister on sprouts & close up of leaf symptoms (Photos R. Bradbury)
Pathogen
Fungus
Hosts
Field brassicas
Symptoms
Pale leaf spots can be seen on the upper leaf surfaces with the associated and corresponding powdery white blisters developing on the undersides of the leaves, these can be up to 20 mm in diameter and can release large spore masses.
Development
Spores can be dispersed by insects, wind or rain splash. Leaf moisture is required for the spores to germinate and pass into the leaves via the stomata. As well as the leaves, this fungus can be found on the stems, pods and florets of host plants.
White blister can survive in a dormant state as an oospore in soil or crop debris. Infected seed can also be a source of infection.
Favourable Factors
Warm, wet weather.
Importance
This disease can infect many members of the brassica vegetable family as well as cruciferous weeds such as shepherd`s purse.
Stems and leaves can be distorted and twisted and individual plants can shows signs of reduced vigour.
This disease can be directly responsible for economic loss by adversely affected crop quality, particularly on flower head and leafy brassicas such as broccoli, cauliflower, cabbage and Brussels sprouts.
Control
Clean seed
Removal of host weeds and crop debris
Rotation
Fungicides programmes should be started at the first sign of infection
Close up (Photo R. Bradbury)
Leaf symptoms (Photo R. Bradbury)
White blister on sprouts (Photo R. Bradbury)
