I have a large established tree in my garden which I think is a bottlebrush of some kind (perhaps you can tell me what it is). Some of the upper branches are covered with a black, charcoal-like substance. Within the charcoal are shiny red bumps that look like sap. Is this a plant disease of some kind? See photo. As far as I know, the tree has not been set on fire or anything. Most of the other branches are fine and the tree seems otherwise healthy. It is currently flowering with fuzzy purple flowers.
Hey Brendan, it a Leptospermum laevigatum or Coast Tea Tree. The black is a sooty mould which is caused by sap sucking insects like scale, aphids or lerps. The sweet sap gets spread around and that's what causes the sooty mould. Eco-oil and Eco-neem will both control a broad range of sap-sucking insects. Spray with either a couple of times to kill the pests. Ensure good coverage all over the plants so you don't miss any of the pests. Once the sooty mould starts to dry and flake hosing can help to remove the flaky bits faster.
Catch it now and your plant will recover nicely.