Posted: Today at 15:03
The lichen isn't a problem and won't affect the trees. I suspect they may have canker though but it's difficult to see from the photos.
What is certainly a problem is that the grass has been allowed to grow right up to the trunk. Grass is a very greedy plant and will be starving the trees for nutrients. It's also possible that feed & weed has been used on the lawn and could have affected the trees because of the closeness of the grass.
What I would do is remove the grass in a circle of at least a metre diameter around the trunks and then sprinkle blood, fish & bone onto the soil, gently working it in, before laying a mulch of well-rotted farmyard manure about 4 inches thick over the soil. This will feed the trees and they should recover providing thay are not too far gone although I wouldn't expect to see much happen until next spring.
Edit: didn'tsee the posts from obelixx and Dove - tend to agree that it might be best to cut your losses and remove and replace them.
Last edited: 29 May 2017 15:08:46