That might have been me, Native. We lost a bunch of apple trees some years ago - back in the 90's - that were growing well. Some members plowed and disked between the tree rows to plant soybeans & clover. The plows and disks got to within 4 or 5 feet of the apple trees and we lost many of them. After some research, we found out that feeder roots for apple trees can go out 20 feet from the tree itself - so we had our answer. No Round-up or other weed spray was used around those trees, so the cultivation was the cause.
In our latest (since 2013) apple & crab plantings, we haven't allowed ANY cultivation near the apple trees and haven't lost one in that orchard. We just have grass growing in the main orchard now, and keep it mowed to help keep mice and voles visible to hawks, owls, foxes, bobcats, etc. Lesson learned.