[UPDATE]
Thanks to everyone for your advice and suggestions it’s very much appreciated. I ended up finding some more evidence such as clear sticky residue on the foliage (honeydew) and discovered it was under attack from mealybugs.
I immediately gave it a thorough spray of eco-oil, and then with the help and advice of my local club we gave it an emergency re-pot into a much better draining mix, as the soil I had it in was too rich in organic material for the climate and rainfall we get down south here, and staying too wet. This mix was fine in a larger plastic pot but not a shallow bonsai pot.
Since this was the first tree I have potted into a bonsai pot - (The rest of my collection are in development), my lack of experience with the shallow container led me to not alter my mix accordingly. What we believe happened is that since re-potting the roots were staying too wet and slowly rotting, in doing so weakening the tree, leading to the mealybugs beginning to prey on it’s vulnerability. I have been told these pests will usually attack a tree that is weakened.
It’s on a daily regime of season now, and thankfully after only one day so far the branches with the dead foliage are already starting to green up again so I think I might have got it just in time for them to be saved. This has been a good learning experience and hopefully if someone else has a problem with their adenanthos woolly bush they can refer here for a possible cause. Just have to remember very good drainage and watch out for mealybugs
