Posted: 08/07/2013 at 11:24
It sounds very much like Woolly aphid, Catherine. These are aphids which exude a white waxy substance to protect themselves. You can gently scrub them off using some soapy water and a small brush or rag. Some folk also use a cotton bud dipped in methylated spirit to kill and remove them. Woolly aphid itself doesn't cause much harm, but left untreated other diseases can develop around the damaged areas.