There are powdery mildew type fungi that you could experience, but the purple or reddish stain is immediately telling that this is not fungus but Wooly Aphids... sometimes called Mealy phids... Here in the U.S. the little critters are covered with a waxy substance which makes them difficult to treat with chemicals.
One treatment that works well here is any product containing Neem Oil. It's made in India from Chrysanthemum flowers. Very eco-friendly. Additionally, repeated treatments of a mixture of warm water, dish soap and a little vinegar will do the trick. Your not the first to surmise fungus when in fact it's these agravting little insects...
Best of luck!