Occasionally and apparently healthy rosette on one or another of my houseleeks will suddenly turn yellow or orange and die very quickly, over just a few days. Rosettes nearby are unaffected. The affliction does not spread from a given point: the whole rosette suddenly capitulates.
Below is an example on Sempervivum ‘Sir William Lawrence’ with one rosette affected
I would be grateful if anyone can tell me what this condition is, though I somehow doubt there is any way of stopping it and it only affects single rosette a few times each year..