is it safe to use lawn weed and feed and moss killer around my apple tree

I haven't tried this, but as long as the weed and feed stuff doesn't touch the apples leaves (which should be higher up!) it should be OK. Does the label say anything? Or email the manufacturer for advice. You should have a circle of soil around your apple tree to stop competition from the grass etc. then mulch with something (bark, compost) to keep down weeds.