Plant Doctor Archive

Sooty mould

I HAVE what looks like black soot on the trunk of my native trees. Is it sooty mould? What can I do about it, apart from cutting off branches that are affected? I try to keep organic if I can.

BLACK sooty mould is caused by insect infestations. Look on the tree and see if you can spot any insects such as mealy bugs, scale or aphids. These excrete a sugary substance called 'honeydew' and the sooty mould grows on this. Ants also feed off it.

Spray with an insecticide such as Yates Nature's Way Pyrethrum. Spray a small test area on the tree, as some natives are sensitive to sprays.

Once you have cleared up the insect problem, the sooty mould will go away. Some native tea trees are more susceptible than others.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.