There are numerous reasons for holes to appear in plant leaves. These include poor growing conditions and environmental stress, insect pests feeding on the foliage and even droplets of water acting as a magnifying glass in strong sunlight.
But one specific type of hole, called shot hole, is caused by plant diseases.
Shot hole is so called because it looks like the leaves have been blasted with shotgun pellets.
Small and more-or-less rounded holes are a result of plant disease infections, especially fungal leaf spots and bacterial canker. The latter attacks members of the Prunus family – such as cherries and plums, both edible and ornamental. The disease causes the part of the leaf that is affected to turn brown and die. This dead portion then falls out of the leaf leaving behind the hole.
Large and irregular shaped holes are a result of poor growing conditions and insectc pests eating the foliage.
For shot hole, improve the plant's growing conditions, which will reduce stress and make the plant stronger and less likely to be attacked. Then control the fungal leaf spot disease or bacterial canker.
Similarly for the larger holes, control the insect pests eating the foliage.