Answer: In most cases it is not a good idea to add soil over surface roots, the roots are raised in search of air or naturally grow in that pattern. Instead, I would suggest you consult with your county extension as to the specific pest/s or cause/s for the dieback and how to care for the trees at this point. Fertilizing often will not compensate for problems and can in fact make the situation worse. They should also be able to tell you what nutrients (if any) are required for optimum conditions for the trees base don the results of some basic soil tests. I hope it is not a serious problem, but I would suggest you do this soon.
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