It is unusual for these plants to suffer from anything, Sjw, as they are as tough as boots. If the plants are alive but just not doing well then I suspect that something is eating the roots eg your leather jackets. Sorry, but I don't know a solution but I am sure that someone will.

Are they newly planted? I was wondering if they were vine weevil grubs if they are new. I'm not suggesting you have your id on the grubs wrong but just a thought.

That seems rather a drastic solution!!!

I'd agree with Seaburn on this. There are other critters that do eat the roots of plants, like vine weevils. There's a good chemical solution to deal with this problem.

Thanks for all your replies, I have looked at the Internet regarding the type of grub it's definitely leather jackets whenever I dig the border over its them that I find, regarding the plants they have been in the border for around three years and have always flourished. I have looked into nematodes but say best treated in autumn so I guess I'll just have to keep squishing them.

I usually cut an old compost bag up and place around my plants, black side down. Next morning I remove the grubs.
They are quite interesting in the fact that they pupate at about 1' down, they move up and down in the soil depending on things like moisture and weather. So there is never a guarantee that you will find the damned things if you dig down a little to investigate. There is no nematode that I am aware of to deal with these critters. But when you get an influx of daddy long legs later in the summer, you will know they have just emerged as adults and are out for plenty of sex. That's the time to beat them down. You will no doubt be able to see them frolicking in your borders, flirting with each other.

We have a troll this morning he has been flagged by several members so hopefully he will be gone soon.

He does seem to have been deleted, Denise. Thank goodness! :-))

:))