I have a trident maple in its third year from seed. Every May, without fail, the growing tips begin to dieback. The dead tips are hollow inside if I break the dead part of the shoot in half. They continue to resprout new growth just below the dead tips and die until around August 1, at which time normal growth resumes.
I assume this is some type of tip boring insects or critter, but no insecticide I have tried will kill it.
Any ideas?