Hi @KazTCB,
Thank you for reaching out for assistance with your flowering gum.
Yellowing leaves can be for a few different reasons, including insect attack, fungal issues, natural aging, watering issues, nutrient deficiency and heat stress. While there is certainly some yellowing, there is not enough for me to be immediately concerned about the health of your tree.
I can't see anything that leads me to believe it is insect-related or fungal issues, but I'd suggest you have a good look for evidence of insects or fungus to rule these issues out. If you can see any gnarled new growth, bite marks or small waxy deposits, please take some photos and upload them so we can have a look.
I suspect the issue is likely due to heat stress, which can be addressed with water and nutrients.
You'll want to ensure the tree is getting deeply watered once a week during the hot months. Deeper watering less frequently will ensure that the trees' roots chase the water down into the soil, which strengthens the plant in the long term. They also don't like to sit in sodden soil, so deep watering less frequently will prevent reactions to overwatering that can result in fungal issues.
I'd also suggest you apply a native fertiliser such as this Scotts Osmocote Native Controlled Release Fertiliser to ensure your tree has access to the nutrients it needs to thrive through these hotter months.
Allow me to tag our knowledgable gardeners @Noelle and @mich1972 to see if they have any advice they can offer.
Let me know what you think.
Jacob
