We have 3 apple trees in our front garden. We moved into the house nearly 2 years ago but do not know how old the trees are. They are quite mature though. We are fairly novice gardeners and in the last few weeks have found a grey sort of bubbly fungus on the trunks of all three (see photo). What is this? Is it bad? What can be done? As well from my readings I suspect the tree may have wholly aphids and apple scab. Is it ok to spray trees this time of year? What’s the best way to do this with such large trees?
More on apple trees at: https://gardenie.wpengine.com/gerrycategory/apples/?id=5389