rosemary hedge`probs - it's`dying!!!

[Pan]

I have a beautiful hedge made of rosemary, which I trim like a hedge every year.
Last year, it was covered in small green caterpillars - which shamefully I omitted to do any thing about at the time... this year, several parts of the hedge appear dead - whilst others thrive as normal... Should I treat the whole hedge, or assume that the winter has killed off the invaders, and if I should treat, what should I treat with? tia.

Arggghhh! Pan I know the answer!!!!
It's Rosemary leaf beetle and my hedge is nearly dead too!
Tomorrow go out and have a loofk for little beetles that look like ladybirds but are black and metallic. They are the problem and their grubs are underground eating the roots.
RHS recommend

sorry posted too early...
provado ultimate bug killer
I picked it up at homebase if you've got one near you.
I've sprayed and now am just hoping for the best, but I'll keep putting a sheet under the hedge and shaking the little buggers out!

Rosemary beetles killed my rosemary too. They're beautiful but deadly. Check tomorrow!

thank you! I am not at home right now, but will be later, and will go a hunting.

I will also set up an automatically-triggered howitzer to blow the little dahlings to peices.

My great (so far unpatented) invention is teeny-weeny landmines which contain just enough explosive to detonate a slug but, for any bigger creature, would feel like a tiny little tickle under the foot. You heard it here first.