I have a Chinese elm around 20 years old which I have owned for 7 years and kept outside for the last 6 years now as it seemed to thrive better outdoors. It is due a re pot but since the extended cold and wet winter we have had in the UK this year it has yet to bud and usually buy this time of year the buds are well broken, it also has a large spread of what looks like Lichen all over the branches and secondary branches. I have never seen or experienced this before and it makes me wonder if the tree has a disease??
Does anyone know what this is and how I can treat it? Any advice is greatly appreciated.