Never had problem with my hedges now white things on leaves and trunk , lady at Mitre 10 said mealy bugs so I bought (congaurd) and have sprayed them every week I just can’t seem to stop Them
Unfortunately your photo was not attached. I think problem is more likely white wax scale, it seems to be in plague proportions this year.
White igloo like scale protect small sap sucking insects. There are various options and a combination of all them is problably your best bet.
1. Remove by hand and destroy - if thery are hundreds/ thousands it is a very long process.
2. Use a systemic insecticide, many people recommend Killa Bug. This is a strong chemical known to affect the tracking radars of bees so should only be used when the plants are not in flower.
3. Spray the branches with White Oil in December and again in January. During this time the young nymphs 'Crawler' come out from the safety of the scale house and disperse along the branches looking some place to settle. This is their most vunerable time and the best time for us to strike.