Posted: 14/07/2013 at 13:08
Ants themselves don't harm apples trees, but they farm aphids which do cause damage. If you look at the leaves on the branch tips, you will doubtless find aphids which the ants have carried there. As aphids suck the sap they produce honeydew as a waste product and the ants eat this.
To prevent ants from climbing the tree, try putting a thick wide band of vaseline around the trunk and cut down any tall nearby plants which touch the tree branches and would allow the ants to find another route up the tree.
You shouldn't allow apples to produce fruit for the first 2 or 3 years anyway so that they can establish a good root system first, so lack of apples on your year old tree is actually a Good Thing.