A photograph would be helpful - are you certain its lichen and not woolly aphid?

If it is lichen, there is no problem. Lichen shows that the air is clean. If like my sorbus, it was hit by the cold and wet conditions it is likely that any buds were damaged. My pink Rowan had few flowers and the berries are very sparse. As bamboo says it might be woolly aphid then a photo would help to identify the problem.