Thank you for advice that I received on this forum to cut back my brown leaved and withering Heucherella, suspected to be suffering from a fungus. I said I would report on its progress and I am pleased to say that it is recovering from its drastic haircut, with a nice head of green variegated leaves.
In the middle of the summer an aquilega was covered in a rust/fungus and it looked so bad that I thought the plant was beyond rescuing. I cut back all the stems to the roots to remove the diseased plant material, intending to dig up the roots and dispose of them too. Well I was busy for a few days and when I returned with my spade the plant was already re-sprouting, so I left it. Within a few weeks the plant had developed a nice new head of leaves again and with feeding has become larger and far more beautiful than before.
The last two issues of gardener's world has given advice on pruning trees and shrubs. I have learnt this year that perenials can benefit from a pruning sometimes too!