You could always try the "non-chemical" route. I have used ant deterrent tape on some of my trees. It stops the ants from getting into the trees to "farm" the scale insects. That reduces the effect of the sooty mould and a small amount of scale can be put up with.
I have a contact for Aust readers, but will not post here. PM me if you want details.

I have also just started using ant trap material in "semi-liquid" form and will be happy to discuss the results of this with people if they ask. (Give it a while to have an effect, though!).
Cheers
John
Tamworth NSW Au

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"I spent most of my money on booze, women and fast cars, the rest I wasted" George Best (arguably one of the best footballers ever!) R I P