It has been quite the year for rust this year, with the buckthorn not only at the garden, but everywhere else in the region, particularly afflicted. However, the hawthorns at the garden, as here photographed by Barry, have also been badly afflicted. Apple trees often get rust covered leaves each year, and both hawthorn and apples are in the rose family, as are the cinquefoils (Potentilla) which I've also noticed with rust on their leaves and stems.