I have suspected that the lumps occurring on this Euc over the years is some sort of GALL. Although none of my other Eucs have been affected I am unsure weather my diagnosis is correct. I have tried various treatments without success and have resigned myself to the fact that this is how this tree will be as it is developed as a Bonsai.
The other thought I have, is that it may be genetic because of the yearly occurrence of what you see in the pics. The new ones will eventually join up with the existing ones and give that gnarly looking trunk.
From memory the Euc is a variety of iron bark.
Any feedback or ideas would be welcome.
Peter
