I also have an ant problem with these bushes, with what appears to be sooty mould but that has abated in recent weeks. I did prune back a bit too harshly last winter - maybe this caused it.
08 April 2012, 01:47AM
The small lumps covering the Callistemon are probably scale insects. These insects have a waxy coating and produce a sugary substance when they feed. This attracts ants to the bush and causes Sooty Mould to develop. The scale can be treated with PestOil and the best time to treat is in Spring when the scale are small. If you apply PestOil you will need to apply a second application about 7-10 later. The help improve the plant's health apply some liquid fertiliser such as Yates Dynamic Lifter Liquid Concentrate which is suitable for native plants.