A number of species of Albugo and Pustula may be found in gardens:
Members of the Brassicaceae, including vegetable brassicas and ornamentals such as honesty, aubretia and Aurinia saxatilis, are affected by Albugo candida. Other Albugo species may also be involved. The disease is also seen frequently on the cruciferous weed shepherd’s purse. On many of these plants it can sometimes be found in close association with downy mildew.
Members of the Asteraceae are affected by Pustula species. Once again it is likely that a number of different species of the pathogen are involved. White blister is the most important disease of salsify and scorzonera, and is found on ornamentals such as Senecio cineraria, gerbera, florist’s cineraria (Pericallis × hybrida) and sunflower. Weeds that can be affected include ragwort, groundsel, goat’s-beard and creeping thistle.
Albugo trianthemae was recorded for the first time in the UK in 2007. It affects the Aizoaceae, and has been found on Delosperma and Lampranthus.
The life-cycles of the various Albugo and Pustula species are very similar. The microscopic spores released from the white pustules are dispersed by rain splash, insects and in air currents. They require leaf wetness in order to germinate and produce a second spore type, which infects the plant through its air pores or stomata.
A third type of spore is formed within the affected plant tissues. This is a resilient resting spore, which can contaminate the soil for several months and germinate to infect new plantings of susceptible hosts. The disease can also be seed-borne.
It is now thought that there are actually many more species of Albugo and Pustula than was previously realised. Until this situation is clarified it is unclear how readily the disease can spread between different plant species in the same family.