Answer: If you have already used insecticide, either the pests that made the holes are already gone, or you have caterpillars munching on the leaves. Do a closer inspection of the tree. If you find little caterpillars you can spray the tree with the botanical Bt (bacillus thuringensis). It is sold as Dipel and works against caterpillars but won't harm beneficial insects. Good luck with your plum tree.
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