From your photo, we surmise that clusters of green leaves from the tips of twigs are falling.  If this is true, the most likely culprits are squirrels.  Squirrels are currently 'planning' their winter quarters and are building what are called 'dreys'  for their winter protection.  Unfortunately, squirrels are clumsy when it comes to transporting their building materials and frequently drop some clusters.
There are a couple of insects that will do similar pruning, both are called twig girdlers and while one creates a clean, convex cut, the other produces a clean, concave cut.  Squirrels leave either a ragged edge or a clean edge, but neither convex or concave.
Whatever the cause, there is no need for concern.  No treatment is necessary.
LS