Poorly berberis - any advice?

I have three berberis plants, which I thought were pretty resilient to just about everything.
I have a red rocket, orange rocket, and pow wow.
All three were doing really well, when suddenly, the pow wow lost all its leaves. I switched it to a shadier spot, and I think it will recover, but it still looks pretty sorry for itself at the moment. (This happened during a heat wave, so I thought perhaps I'd forgotten to water it when I watered the others - sometimes it's hard to keep track!)
Now my orange rocket is showing some signs of distress. At the moment, it's just the very tips of the tallest shoots that are starting to wilt (with new leaves on them, they've just kind of keeled over).
I'm worried that the same is going to happen to my orange rocket. The red rocket is still looking fine.
Any ideas what can have happened to the pow wow, and if the same thing could be happening to my orange rocket? I can only think that they might not like full sun exposure, as the red rocket is in a shadier position, but I thought berberis wasn't supposed to be picky?
I'll take a pic of the poorly plants later, if anyone can help...

 

Have you checked for greenfly? My berberis always get covered with the little blighters at this time of year.

 

No greenfly or other beasties. I do have some aphids etc in the garden, but nothing excessive, and none on the berberis.

 

After gardening for many years I find the best thing for Berberis is to cut them down along with all thorny shrubs

 

Over the years I have had a couple of Berberis up-and-die for no apparent reason. Maybe they are short lived?

 

Well, the pow wow seems to be recovering, and I think will regenerate eventually. I gave the orange rocket a really good soaking last night, and today it rained for most of the morning, and most of the wilted stems have perked up.
The pow wow was previously on the 'sunny side' of the garden, until I moved it to the shade. The orange rocket is also on the sunny side, and yesterday was a hot day when it began wilting. The red rocket is on the shadier side and has had no problems whatsoever. So I can only conclude that despite planting instructions that say they like 'full sun,' my garden is too sunny for them, and they want to be positioned in the shade. Which is fine, although contrary to what I'd believed about berberis - I thought they were supposed to thrive in all conditions. So I'll have to do some shuffling about (luckily, I have a container garden!).

 

Glad my diagnosis is correct! I love the berberis for their colours, though it's a shame they don't seem to like full sun after all. Not a problem, I shall shuffle them all over to the other side, where they'll only get sun later in the day.