How to treat gum tree with galls?

[JemW]

So sad! Something is attacking my gum tree and has depleted it in the last week. Can you please help? 

 

 

[JacobZ]

Hi @JemW,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

It is difficult to say from these photos alone, but it looks like it could be something like galls or scale.

Is it possible to get a better photo of that first branch with the lumps on it?

Are there any other abnormal growths on the tree anywhere?

Seeing the issue a bit more clearly would certainly help us identify it and offer steps moving forward.

If it turns out to be gall, then the best approach is to have the affected branches removed and destroyed. Due to the apparent height of the tree, I would be contacting an arborist for their assistance with this.

Allow me to tag @mich1972 and @robchin to see what they think.

Jacob

[JemW]

Thanks Jakob. 

Here's a close up. 

  

[JacobZ]

Hi @JemW,

Yeah, they look like galls, which are caused by small insects such as wasps or flies laying eggs just under the surface of the bark.

I would suggest cutting off the affected branches and destroying them, then focusing on the overall health of the tree.

You can apply some native fertiliser to the tree and ensure it is well watered to help promote overall health.

Outside of this, I don't think there's much else you can do besides monitor it.

Let me know what you think and if you have further questions, please don't hesitate to reach out.

Jacob

[JemW]

Thanks Jacob. 

So it sounds like the poor tree is pretty much gone...

Can you please tell me what cause this and how to prevent it from occurring again? 

Thanks 

[EricL]

Hello @JemW 

Galls and small insects such as wasps or flies lay eggs on gum trees as part of a survival strategy that provides food and shelter for their developing young. When a female insect injects her eggs into the tissues of the gum tree, often along with specific chemicals or enzymes, the tree responds by producing abnormal growths called galls. These galls are essentially the tree’s own tissue, but they are hijacked and reshaped into a protective casing around the insect larvae. This benefits the insect because the gall not only shields the eggs and larvae from predators and harsh weather but also provides a nutrient-rich environment that the larvae can feed on as they grow.

Deterring gall-forming wasps and flies from laying eggs on gum trees is difficult because they are highly adapted to the tree. The best approach is to focus on overall tree health, since strong trees can tolerate galls without long-term harm. Regular watering during dry periods, mulching to protect roots, and avoiding unnecessary pruning or stress will make the tree more resilient.

For young or small trees, you can prune and remove heavily infested branches before the insects emerge, disposing of the cuttings away from the garden. This reduces the next generation of gall-formers but must be done with care to avoid over-pruning. Encouraging natural predators such as parasitic wasps, predatory beetles, and birds also helps keep populations down. Planting a variety of native shrubs and flowering plants nearby can attract these beneficial species.

Horticultural oil sprays, applied at the right time, may discourage wasps from inserting eggs into fresh growth, though this is more practical on smaller ornamental eucalypts rather than tall mature trees. Overall, gall formation is a natural process and usually doesn’t seriously harm healthy gum trees. Managing stress and supporting natural predators is the most sustainable way to reduce infestations while keeping the tree vigorous.

If you need further assistance, please let us know.

Eric

[robchin]

HI @JemW 

Sorry I'm a bit late to this one. Some good advice from Jacob and Eric below. Don't despair - I don't think it's going to kill your tree. If you manage the pest and keep the plant healthy it should come away OK. The insect pests will die or leave the plant. A couple of other suggestions:

1) Physical removal - old-school. Scrape them off if you can with your fingers or a paint spatula.

2) Spray - I work at Bunnings and we do sell an insecticide that may help if you have no luck with the oils recommended below - looks like those hard casings will be hard to penetrate so something like this spray may be worth a try. Yates 50ml Advanced Garden Insect Killer - Bunnings Australia

Good luck.