There is a black soot falling from our golden wattle, this has fallen onto a barbeque, the lower leaves and branches of the wattle and the paving stones beneath the tree.
There does not appear to be an aphid infestation on the tree.
Does anyone have any idea what this is from or how to treat it?
Thanks,
Edward
The black soot is likely to be sooty mold that grows on the honeydew secretions from various sap sucking insects including various soft scale, aphids, psyllids, mealy bugs and white flies.
Systemic insecticides will successfully kill the sap suckers you can then hose all the sooty mold from the leaves.
Ants love honeydew and are commonly seen over infected plants, they farm and protect the honeydew secreting insects, stopping the ants allows the other predators to eat the insects. Using a barrier, like Tree Guard around the tree trunk will prevent the ants climbing up and down the trunk.
The big question is - How big and old is the tree? Acacia have a short life span and as they age become more susceptible to pests and disease, if the tree is old it may be better to remove it and replant. Secondly, if tree is very large it is not really feasible to spray the whole tree and using insecticides will kill all the insects living on the tree.