Horse chestnut tree leaves
Thank you for attaching the image of your leaves. They have powdery mildew, a disease common on various kinds of plants during the summer. The best that can be done is to rake and destroy affected leaves.
Sprays are only effective when applied at the very first indication of disease. And if this a large tree, it’s wise to hire a tree care company to do the job
It’s worth knowing that leaf loss late in the year is unlikely to damage the tree’s health. It will leaf out normally next year.
If you choose to spray the tree in the future, we suggest you hire a Certified Arborist for the job. You can locate such a person/company by searching with your zipcode at www.treesaregood.org.