Another tree virus to look out for, Julie Bolton (County Arboriculturist, Environment & Heritage Team, Planning Services, West Sussex C.C. ) writes:
I’m sure you’re aware that trees are vulnerable to viruses too so I just wanted to let you know about European Mountain Ash Associated Ringspot Virus. A bit of a mouthful and nothing to do with ash, i.e. Fraxinus; this affects Sorbus aucuparia otherwise known as rowan, and some other Sorbus sp.
It’s a foliar pathogen and most visible in late May, June and July so the next few weeks might be the time that you see it. Because it affects the leaves, it can result in reduced photosynthetic ability leading to a lack of vigour. It’s often seen on grafted trees and was first found in the 1960s but seems to be on the increase; perhaps because it is widely used in planting schemes and stressed trees are more vulnerable, as with any infection. Secondary pathogens like honey fungus can then cause the eventual demise of the tree.
It isn’t a notifiable disease but Forest Research and others would like to know about it so if you do see it, please report it via Tree Alert. It can be mistaken for other foliar conditions so check the signs and symptoms here:https://www.observatree.org.uk/portal/european-mountain-ash-associated-ringspot-virus/
There is also a great downloadable leaflet to help identify it HERE