I live a new build house - the builders planted a young rowan tree in
the front garden.

In summer, it started dropping leaves and although it never dropped them
all, the tree looks a bit limp and poorly.

At the same time (and again this morning) I found grey dagger
caterpillars on it.

Firstly, should the rowan have dropped its leaves so early, and second,
how harmful is the caterpillar?

ta,
g.