A true organic method of looking after apple trees is to apply a grease band around the trunk. It stops codling moths from climbing the tree in spring wich leads to maggoty apples in autumn.
Another benefit is that it stops ants patrolling the tree, farming aphids and keeping them safe from predators. This can seriously weaken a young tree, so getting rid of the ants is a very good move.
Grease bands can be purchased as adhesive paper strips (Bayer Boltac Greasebands are the only brand in my local garden centres) and these are good for younger trees with smooth bark. I personally find that because they have to be applied sticky side out, they are a pain to get right, but it is so worth the effort that I just take a deep breath and get on with it. You have to put a wire loop at the top and bottom of the band to ensure that it is tight against the tree’s trunk. Remember to remove it at the end of the autumn and replace in late winter, otherwise the wire may start to dig in to the growing bark, harming the tree.
Once the bark gets knobbly and fissured, the moths and ants can find their way up beneath the paper strip, so with older trees, brush the grease directly onto the tree in a three inch wide band, right around the tree. This is easy to do, but the grease is horribly sticky and cleaning the brush after use is a practical impossibility.
Whichever you use, the tree will love you for it and remember that this is also good for pears as well as apple trees.
However, do not leave a band on for longer than directed on the pack. We forgot about one and when we eventually did remove it a year later the tree had suffered quite a bit beneath the band. Thankfully once exposed to the air it soon sorted itself out but I think we had a lucky escape.