Symptom
Young fruit dropping
Plants shed fruit they cannot support after stress, poor pollination or pest attack. Some drop is natural: many fruit trees thin themselves in early summer.
Cut a fallen fruit. Grubs inside point to pests; seedless or undeveloped fruit to poor pollination; healthy fruit to stress or natural thinning.
Likely causes
Ordered from the usual answer to the less likely one. Each links to the full problem.
Recorded on Hydrangea
Less likely on Hydrangea