Certified GKH Gardening Expert
That is a severe spider mite infestation. This is very difficult to get rid of at this point.
You will have to proceed with treatment, VERY CAREFULLY, if this is a grafted tree. If this is from seed, then you don't need to worry as much. A grafted tree's top, or scion, may fail leaving you with rootstock only, after treatment. This will not be the same tree that you have purchased. If it is from seed, then the entire tree is the same, so it won't matter if it comes back from the root.
Here are some articles that will help: