Young apple tree not growing, maybe due to mildew?

I have a small apple tree (about six inches tall) that I recently had to treat for powdery mildew. The lower leaves are mostly okay, but it has a few top leaves that are pretty deformed because of the mildew. For about a week and a half now it hasn’t produced any new growth. It seems to be doing okay otherwise, it’s just not growing. The other apple tree I have had the same problem and is growing just fine now (they were planted at the same time). I’m not sure what to do. Should I just wait longer and see if it starts growing again? Any advice would be much appreciated. Thank you so much!

In many parts of the U.S. winter is coming on and deciduous trees such as apples are going dormant for the winter. Where are you located?