The powdery mildew pathogen Podosphaera pannosa also attacks roses and a distinct variety attacks peaches. Podosphaera tridactyla is found on numerous host species of the genus Prunus. As with other powdery mildews, these species grow initially over the leaf surface, feeding from the tissues but not killing them, and producing white, airborne spores which spread infection. Later the tissues die and, unusually for powdery mildew infection, drop out leaving holes and tattered edges to the leaves. An overwintering stage is of minor importance, most survival through the winter is as mycelium on the evergreen leaves.
The shothole fungi survive the dormant season in lesions on twigs, buds or leaves and produce spores that are mainly dispersed by rain. Infections occur in young leaves, but as they expand the infection stabilises and the healthy leaf tissue pulls away from the lesion which drops out, leaving a hole. Severe attacks result in a ragged appearance to the leaves. Stigmina carpophila attacks other Prunus species but Eupropolella britannica has only been recorded on Prunus laurocerasus.
The bacterium Pseudomonas syringae is readily spread in wind-driven rain and penetrates host tissues through natural openings or wounds. The bacteria survive on plant tissues when the conditions are unfavourable to multiplication and infection.
The bacterium Xanthomonas arboricola pv. pruni also affects Prunus species (including laurel) and although not thought to be established in the UK, there was one infected plant confirmed by Fera in 2013. The disease is established in several European countries, where it has also been found affecting commercial production of Prunus laurocerasus. Symptoms include shothole, fruit and leaf spotting, stem cankers and severe defoliation.
Any suspected cases should be reported to APHA – The Animal and Plant Health Agency Telephone: 01904 405 138 Email: firstname.lastname@example.org