I have a hedge of wax myrtles, Some of them look like they were burned (leaves brown) this does not affect the whole plant in most cases just several branches. The home owner said they have a disease. They said their neighbor had the same problem and ended up cutting the whole hedge down. Of course we are not to that point yet. I called my local nursery ad they said they were not aware of a disease of wax myrtles. The rest of the leaves look normal. BTW we have been 30 something days without measurable rainfall. WE did finally get some rain a whole weeks worth. Things are starting to happen again now.