I'm not sure about the gypsum, but I have another idea to protect your maple tree leaves.

There is a product called Cloud Cover, and you spray it on the leaves. Best to do it in the spring when the fresh foliage emerges before they get crispy edges but at any time it will help protect the plant's beauty.

Maples have leaves with very thin cellular walls so they transpire very quickly, and it is hard for them to retain moisture. Cloud Cover is a liquid wax that helps seal in the moisture. Really works!