WHAT IS THE WHITE FLUFFY STUFF ON MY APPLE TREE

Woolly aphid. I dont know of a cure bu if the trees are healthy and there aren't masses of woolly ness, then the trees shoud e able to cope. If there are lots, you could perhaps squash them with your fingers, or rub them off unless the trees huge..

If it is woolly aphid (scrape one off and look under the wax for the insect hidden under a tiny 'oyster shell'), then small infestations may be removed with methylated spirits and a stiff paint brush. Otherwise you are into washing the tree with Winter Tar oil substitute (actually now a horticultural soap) and a power spray.
These DO affect the tree by a. sucking out the sap, and b. They carry virus in their mouth parts which can severely weaken your trees.
It takes a while to get rid of them all so you do need to repeat the treatment.
Also use the Winter Oil later on to kill off the crawling stage of the insects before they form the waxy covering. It is reasonably organic by the way.