Hi Louis,
Curious if you may have a problem with your soil in some areas. Where you have had failures, have you replanted with new plants and they lived? I had apple trees and always had an area where the trees seemed to die within a few years. after several tries took soil samples and found that there was a natural enzyme in the soils that was killing off the new trees. Removed yards of soil and replaced with new and trees took hold.
Edit your profile and add where you are from.
Craig