I dumped my shopping in the car and wandered off in the direction of Homebase (there are some convenient conveniences there) passing some scruffy blackthorn shrubs at the edge of the car park. The leaf margins bore pustules caused by a mite, Eriophyes similis. This will occasionally attack domestic plums but, other than being disfiguring, it causes no harm.
Unsightly but causing little harm. Eriophyes similis causes pustules
on leaves of blackthorn. Daventry town centre. 21 August, 2018