I have a plum tree, which I planted a few months ago. It has been very healthy and growing nicely till today. This morning I noticed some of the leaves had fallen of and a lot of the leaves have brown marks on the top side of the leaves.
Problem Plum Tree Leaves
Certified GKH Gardening Expert
Are these marks squiggly? If so, it is leaf miners. This article will explain more about them if this is the problem:
If this is not the problem, let me know what shape these marks are. That will help with identifying the problem.