It seemed to happen almost over night. Leaves on ground are green, not yellowing. Another holly bush 20 feet away is fine. Have had these bushes for years without a problem.
Holly Bush Is Losing Its Leaves
Certified GKH Gardening Expert
Disease or infestations would usually show some other indications on the plants.
Damage to leafs or discolorations.
Could the plants have been had an accidental spray from a herbicide?
Also if the plant is suffering from drought it could drop leaves, but generally yellowing of leaves would precede this event.