What laid white eggs under leaves of prunus ‘Kojo-no-mai’?

PAMELA MCNEIL, BY EMAIL

AThis is hydrangea scale. The adults tend to inhabit the shrub long before you spot their waxy, cottony egg masses and persist long after the eggs have hatched. So, cutting back your plant severely can remove most of the problem, though the shrub may take time to recover. Try spraying with an insecticide once the plant starts making new growth to ensure no pests remain.