Mildew on my Apple Tree

Just recently planted a Red Falstaff apple tree in the garden and I noticed a touch of what looks like powdery mildew on a few leaves - what's the best treatment? I'd rather not go and buy a spray but I'm not totally against it, but would prefer a 'traditional' route - any one have any suggestions? Many thanks, Jude.

I read that it was caused by the tree not having enough water - my first case of it last year - though not bad so I just pinched off the tips that were affected