There are several fungal problems in orchards that can be made much worse if you don't clean up the leaf litter. That becomes the source for next season's ascospores.
If you pile them up and mulch over them, that controls the release of the ascospores next spring, and helps it all rot faster, so the good fungi and other flora and fauna can beat up and kill the bad guys.
If you have a complex designed "mess" that doesn't have a bunch of
apple trees all together, and a bunch of other stuff all interspersed around the
apple trees here and there, that
should help, but I have no direct
experience with that.
HTH
troy