Hi Kathy and thanks for your picture and question about powdery mildew on your apple tree. It looks like a classic case so I'll include an article about the disease. You can cut off the branches affected if there are not too many and destroy them -trash, not yard debris bin.

If you fertilized the tree this spring the extra nitrogen is not helping, and you will need to prune this summer or next winter to open the tree to air flow.

There are five products listed for home treatment in the article. They are the ones with an H in a square after the product name. Four are chemicals and one is biological so rotate which ones you use if you decide to go this route and follow the directions VERY CAREFULLY. For example, Spectracide Immunox says to not spray within 2 weeks of harvest!

Some years are just worse than others for powdery mildew and your tree may be fine with just the affected branches removed. Just note that there are resistant varieties if you need to eventually replace the tree.

https://pnwhandbooks.org/plantdisease/host-disease/apple-malus-spp-powdery-mildew
Good luck!