Pear-leaf cluster-cups

Every two to three weeks I make the 220 mile round trip to Oxfordshire where my parents - both in their mid 90s - live in their tiny bungalow. They are now too frail to maintain their garden but haven't been able to find anyone locally to help them out. Hence my gardening trip. I noticed this barnacle-like growth on the leaves of their pear tree this afternoon and remember seeing it in a recent blip by Dancersend(https://www.blipfoto.com/entry/2099152072665468712). Without blip I wouldn't have known that its a rust fungus called Gymnosporangium sabinae or 'pear-leaf cluster-cups'.