I'd take a couple or three cuttings, Steragram - semi hardwood are the ones to do, according the RHS. It sounds as if its got a root/butt problem, probably fungal, most likely phytophthera of some kind. It will kill it, quite possibly, even though there's not much to see. Check the base of the stems for sogginess. I'd say dig it up and check the roots, but its been in 4 years, so its probably better to try to get cuttings going in case the whole thing dies.

Oh dear, what a shame. Would the phytophthera kill any replacement shrub too, if that's what it is?
No sogginess at the base of the stems.

If I were to check the roots what would I be looking for?

I wouldn't check the roots, there may be nothing to see - try to raise new ones and if the original dies, then dig it up and inspect. Usually, fungal infection like phytophthera, when it presents in this fashion, affects the plant at the base of the stems - you may find darkened areas, and it may affect the roots and be visible, or it may not. What you will see is die back, drooping, that kind of thing. It's usual to remove some of the soil if you suspect phytophthera when you take the plant out.
Whatever it's got, there's clearly something fungal going on.

I just had another awful thought - its only a yard from a young magnolia stellata, about 4 feet tall, that was given to me by the son that died a year ago this week, and is consequently precious. (That's the main stem, the top is much nearer than that) Do you think there is any danger of it being affected, and if so is there anything i can do to prevent it?
If I do have to dig up the prosanthera would the infection remain in the soil and affect any other shrub that replaces
it, and would adding a high nitrogen feed help?
Sue

If, as I'm sure it is, the Magnolia is much more valuable to you than the Prostanthera, I'd remove the latter asap. Maybe you could find a large container and pot it up in that to see how it does. If it has a fungal infection caused by phytophthera, then yes, it could spread and cause problems. Remove some of the soil which was round the roots from the ground, as a precaution.

What a horrible task - I was so pleased with it. Still, needs must. Does the fungus attack any shrub or tree, and does it attack perennials?

Plenty of phytophthera about, attacks plenty of plants. Great swathes of Larch have been removed in various parts of the country because of attack by one of the phytophtheras. Less common in non woody plants, more common in wet seasons. Which might explain why yours has a problem this year...

With all these recently introduced diseases around it makes you wonder how much will be left growing in another ten years or so.

Its one of my interests, new diseases/pests - I have a list stored to which I add whenever I hear something new. Makes depressing reading, lol!

What a gloomy hobby! Very useful to the rest of though.

Ha ha, I suppose it is - but its in my nature, being what's called a 'hyper vigilant' personality. Think meerkat on guard, always scanning the horizon for what's coming next! Its quite tiring, but seems to be an ineradicable part of my childhood 'programming' unfortunately.

Goes with your avatar really, tall and straight!

Tall, oh, if only. 5 feet 4, most of my life, now shrinking - 5 3 two years ago, probably 5 2 by now, can't reach the herbs in the cupboard any more. Compacted arthritic spine, but it happens to us all eventually. Guess it helps if you were tall to start with though, lol!

Count your blessings dear - I started off at five two and a half and keep a small stool in the kitchen now.

LOL, believe it or not, that Mothercare step for my kids to reach the toilet that I was going to throw away when I moved here is permanently in the kitchen now - I use it all the time, gives me an extra 4 or 5 inches!

Oh I believe it. Mine is a very ancient wooden stool, very much worse for wear that has been in my family since before I was born. When the removal men brought it into the kitchen of our present house i swooped on it with cries of joy as it meant I could put stuff away - they gave me a very odd look indeed!

Ha ha, I bet they did. I've got a short stepladder, but its easier to just kick the step into the right place for reaching the top shelf in the cupboard. My sons think its hilarious, that step is 32 years old, and they remember it well.

I kick my stool around too, poor thing. At 32 your step is a mere chicken! Your sons would have laughed at me too yesterday, balancing on the worktop, holding onto the top of a cupboard door and wiping the pine ceiling to find out if it was dirty - and hurray, it wasn't!

Oh lord, now that's the sort of thing we're not supposed to do, balance on worktops! 'Elf and safetyin the home dictates the use of a proper set of steps, for heaven's sake be careful. Although having said that, I do very similar things myself, lol

I know, but don't you get fed up with that particular elf?
OH was standing by to hand me down.

Ah, well I guess OH's do come in handy - but I don't have one of those, has to be the ladder for me then!

Tough - but then you don't have all the extra laundry...

I don't think I ever told you - it turned out not to be phytophthera after all, thank goodness. It i did tell you, just put it down to senility. Again.

You did tell me,but I'm damned if I can remember where, cos its not in this thread. We're as bad as one another, Steragram, lol

I hope not for your sake...