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Hello,
My eucalyptus has a lot of spots and looks poorly what kind of disease might it be and how can I treat it? I believe I am having similar issues with many plants in the garden.
Hello @bubbyduck
Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your eucalyptus tree.
From the photos, it looks like your eucalyptus is showing signs of stress that could be related to fungal disease, insect damage, or environmental stress. The brown, round galls on the stems are a clear indicator of eucalyptus gall wasp. This pest is very common on young eucalyptus trees and causes the tree to produce galls on leaves and stems, leading to distortion, dieback, and overall poor health. The red and brown spotting on the leaves may also be linked to fungal issues such as Mycosphaerella leaf spot, which is common in eucalyptus when conditions are humid.
The galls along the branches are almost certainly from gall wasps. They lay eggs in the soft tissue, and the plant reacts by forming these swollen lumps. This weakens the tree, diverts nutrients, and makes it more vulnerable to secondary infections. The spots and patches on the leaves are likely fungal in nature, especially if you are noticing similar symptoms on other plants in your garden. That suggests your garden may have a high fungal load in the soil or air, often triggered by damp or crowded growing conditions.
Unfortunately, there is no simple chemical cure for eucalyptus gall wasp. The best approach is cultural and biological management. Prune out and destroy (do not compost) affected branches to reduce the gall wasp population. Encouraging beneficial insects such as parasitic wasps can also help naturally reduce numbers. For fungal leaf spot, improve air circulation around the tree by pruning nearby plants, avoid overhead watering, and collect and dispose of fallen leaves. A copper-based fungicide such as Yates 200ml Liquid Copper Fungicide or Yates 150g Mancozeb Plus Garden Fungicide And Miticide can be used on new flushes of growth if the fungal problem becomes severe, but focus on prevention first.
Since you mentioned that many of your plants are experiencing similar problems, this points to either high humidity, poor airflow, or stress conditions in the garden that make plants more susceptible to pests and disease. It may help to thin overcrowded areas, improve drainage, and check soil fertility. Applying a layer of mulch can stabilise soil moisture and temperature, but keep it away from plant stems. Also, be careful with fertiliser use; too much nitrogen encourages soft growth that pests love.
If you need further assistance, please let us know.
Eric
Thank you. The grey irregular shapes spotting is not pest damage? My larger parent gum tree also has this leaf damage and now has substantial kino seepage on the trunk. I’m not sure if I need to make a seperate post for each plant or species but I am worried about Phytophthora although I don’t think that’s associated with spotting? My other larger eucalptus has red spotting on the leaves as well but no sap issues. I have found small caterpillars on the leaves of one. The canopy on both the large gum trees looks good. I previously had issues with overwatering the lawn with duck pond water (it developed grey leaf spot), and allowing the grass and plants to be overgrown. The overwatering was stopped 2-3 years ago, but the plants have just gone downhill steadily or some appear to be stunted growth wise. I had some grevilleas with mold like spots on the leaves and trunk that had severe foliage die back that I just pulled out. Others like lomandaras have just seeded into more plants and appear to be fine. The lomandras had crowded out the base of the larger gum trees which I assume gave a mulch like affect that isn’t good for them. I also have two acacias that appear to be suffering from severe dieback of the leaves but no spots.
Hello @bubbyduck
Thank you for providing those extra photos of your eucalyptus tree.
I can see why you are concerned. Let’s break this down based on the photos and the symptoms you’ve described.
The grey, irregular patches and mottling on the eucalyptus leaves look more consistent with chewing or skeletonising insect damage and possible fungal or bacterial spotting rather than being a direct indicator of Phytophthora root rot. The small caterpillars you found are very likely a primary cause of the leaf chewing. Eucalyptus trees often host leaf-eating larvae such as sawfly larvae (spitfires) or various moth caterpillars, which leave patchy holes or irregular areas where the leaf tissue has been scraped off.
The kino (red sap-like resin) seeping from your larger gum’s trunk is a different symptom and usually indicates stress or wounding. Kino exudation can be caused by insect borers, fungal pathogens (such as canker-causing fungi), mechanical injury, or environmental stress. It is not diagnostic of Phytophthora by itself. Phytophthora root rot typically shows up as crown dieback, reduced canopy density, yellowing leaves, and poor new growth due to root decline, not spotting on leaves or kino on the trunk.
The decline of your other plants such as grevilleas and acacias raises a flag, because they can be highly susceptible to Phytophthora. The fact that your lomandras are thriving while grevilleas and acacias suffered could point toward soil-borne pathogens like Phytophthora or waterlogging stress in the past, since lomandras are generally more tolerant of heavy conditions. Your history of overwatering with pond water and having dense groundcover around the base of the gums could have encouraged root stress and fungal pathogens. The grey leaf spot on your lawn indicates fungal activity was present in the system.
At the same time, the good canopy on both gum trees is reassuring. This suggests that although they are stressed, they are not in rapid decline.
Here is a practical approach you can take:
- Monitor the caterpillars and consider physically removing them.
- Prune away any dead or severely affected foliage from the smaller plants to improve air circulation.
- Avoid mulching directly against the base of the gum trees, since this holds moisture at the trunk and can worsen fungal issues.
- Make sure drainage around the trees is as good as possible.
- If you are still concerned about Phytophthora, you can have the soil tested or leaf samples assessed by a local plant pathology lab. If symptoms become worse, I recommend engaging the services of a local arborist.
If you need further assistance, please let us know.
Eric
