Is your blueberry plant suddenly leafless?  If you can still see stubs of leaf petioles attached to the bare twigs, chances are the damage was caused by yellownecked caterpillars (Datana sp.). On blueberries, "Datana worms" eat every part of the leaf except the last little stub of the petiole. They tend to strip one or two bushes entirely and leave nearby bushes untouched.

See the link below for additional information.  if you see clusters of caterpillars, it may be easiest to just remove branch and all, before they do too much damage.

Defoliation at this time of year (August) will reduce blueberry yield the following year. This is because blueberry flower buds are forming from now until cold weather, and buds will not form on stripped bushes, except on a late weak flush of growth that may appear as a stress response. With few berries forthcoming, this winter will be a good time for a hard pruning of affected plants to stimulate new vegetative growth the following Spring.

For more information review the Factsheet on Yellownecked Caterpillars.