Im sorry I just found your question. I think you have the same problem I do and it's a plague called GLASSY WINGED SHARPSHOOTER, small black insects that look like a big staple. I found and article the internet that says spraying "IMIDACIOPRID" is the solution to that problem.Also  "YELLOW STICKY TRAPS"  100-200 feet apart  that have to be replaced every two weeks. Hope this helps and believe me I feel your pain.