BigBill said:Most likely scale insects. Bayer's 3 in 1 spray. 3 applications a week to ten days apart.
The OP is in Australia and so any specific pesticide suggestions would need to be available there. So far I'm not finding it but Google always insists on giving me Canadian results for the most part, even though I included Australia in the search terms
You can get all kinds of pesticides for home use there in the USA that are not permitted/available in other countries.