My tree is continually losing leaves which are a brown and yellow colour with rough black dots on. Bark healthy and new leaves still growing.
This is called black spot fungus. It is not normally fatal to plants but does look unsightly. Treat the plant with a fungicide and this should help clear it up. If possible, water it from below, rather than above, as overhead watering can aggravate the problem. This article will also help:
https://www.gardeningknowhow.com/plant-problems/disease/black-spot-fungus.htm - See more at: https://questions.gardeningknowhow.com/tag/eucalyptus-plants/page/9/#sthash.i7W8jNAk.dpuf