Plum tree leaves
What is eating my plum tree's leaves?
Certified GKH Gardening Expert
Plum Trees can have several pests and disease issues.
In the spring Plum Trees can be attacked by Tent Caterpillar and Gypsy Moth. Japanese Beetles can also attach the tree.
Inspect the tree and look for signs of these pests.
Here are some links with more information.