1.) Chuck the whole lot away. Nothing lost with D.capensis (Hey! I'm
a beginner, I wouldn't mind keeping some!)
2.) Drown them in water, well-away from any other plants.
3.) Could be mealy bugs.
Had a look with a magnifying glass. Most are dead, but there are live ones on
the live foliage. (the dead ones being mainly on the dead foliage!)
The LIVE beasties look very much like greenfly (ie. aphids) although white!
So, I think they're whitefly rather than mealy bugs. Also, the plants are
dew-less ATM. Its possible that they were underwatered - partially de-dewed,
the whitefly got a hold,etc.,etc.
Anyway, I'm going to tidy them up, pot the died-back ones on (something I
should do). Dunk the whole lot in water, and see what happens. If nothing,
they're going out in the snow! <fx: evil laugh>
Richard