The leaves on my young tree have holes in them as if they are being eaten by insects but there is no sign of insects
B. Black Mulberry Tree
Certified GKH Gardening Expert
This may be a mild case of Cercospora leaf spot or the beginnings of another disease. Cercospora leaf spot causes brown spots on leaves which can also develop into small holes, and some leaves may fall off. It shouldn't hurt the tree unless the symptoms are severe.