Are the white patches easy to lift off or attached firmly to the leaves? If they are a bit fluffy, easy to lift off and stain red when squashed they are mealy bugs. If not hope somebody else knows!

Welcome to GoY, Nicolette!
Do you know which species that "ice plant" is? It doesn't seem to match the specs for a true Mesembryanthemum, which is now a genus with only one species. Knowing the true species, or even genus, of the host plant can help greatly in tracking down which pest is attacking it.
A closer picture would also help. What I can see makes me think that it is a scale insect, but a mealybug is also possible, in the slight blurriness.

I think that it is Delosperma, Ice Plant. Could it be mildew, we can't tell from the photo? It certainly will not like the cold & wet, I'm presuming it is growing outside.

Just noticed that the enquirer is in South Africa. Perhaps there might be problems of this sort that we don't have in the UK?