Powdery Mildew Oak seedling

Hi,
I have 2 acorn seedlings in their second year and both have had powdery mildew this year. I have treated this year organically but don’t know how successful this was. I was wondering if this will die off over the winter (UK) or if they will need to be treated repeatedly? Currently planning on keeping then outside unless inside would improve this. Thanks

when the leaves drop it will disappear, no do not take them inside. I don't bother to treat it does no real harm.