hey ruby.. welcome to GW ... we like to teach .. so come back often ... i am relying on the prior ID ... you will probably get a lot of abuse as to the prior owner choice of plants ... if you use the GW search function.. you might find a couple hundred posts about how bad these trees are ... that said 2 things.. first.. its fall .. the leaves will be gone within a month or so.. IGNORE this COSMETIC problem ... as noted.. it comes and goes based on weather.. and ma natures whims.. it is NOT something you treat.. nor worry about ... especially on this aggressive weed .. second ... you already have a tree that is not structurally sound.. due to the fact that it is multi leaders low to the ground.. and it appear to be growing away from i am going to presume is shade.. its leaning to the right significantly .. which is going to make the above structural problems happen even faster.. perhaps a pic from a bit further back will give us a better idea of what is going on ... that said.. got anything else you need opinions on.. i am full of such today .. lol .. [though some may suggest i am full of something else.. lol] welcome ken

I believe that's lichen or moss. I doubt it's the reason for your sickly apples. Check out videos by Stephen Hayes on youtube. He is based in the UK and has some great videos about rehabilitating old apple trees there. His trees look a lot like yours.

I see nothing wrong with your tree that would require any treatment. There are some blemishes on the leaves but that looks more physiological than any sort of disease or insect problem. There might have been some early aphid activity but don't see any sign of them now - aphids often attract ants. Regardless of the cause, the tree will be fine. FYI, the Bonide sulphur spray is intended to be used as a fungicide. It will have no affect on any insect problems, should they arise. Any apples the tree produces should be fine. You do have a pollination partner for it?

I agree. looks like scale. Spray with neem oil or horticultural oil.