The gorgeous nectar-filled flowers of grevilleas add colour to our gardens and keep our native birds happy.
But, grevilleas can suffer from various problems, pests, and diseases.
The most common problems that grevilleas have are fungal diseases including leaf spot, leaf blight, root rot, cinnamon fungus, and sooty mould.
Another common problem can be related to overfertilising with phosphorus. This can result in burnt leaves and can be fatal for the plants.
Let’s have a look at each of these problems in more detail.
Common fungal infections in grevilleas
As mentioned, there are various fungal infections that can affect certain species of grevilleas.
Here’s how to identify them and how to fix them if possible.
Leaf spot or leaf blight
These fungal diseases will be more prominent in grevilleas grown in humid areas.
They are caused by the Cercospora and Phyllostica fungi:
- Grevilleas infected with the Phyllosticta fungus usually exhibit yellowing leaves with irregular grey, black or brown spots.
- On the other hand, the Cercospora fungus will cause the leaves to turn light brown or bronze and eventually grey.
If you look closely at the leaves, you will usually see evidence of the fungal spores. These fungal diseases are the main cause of grevillea leaves turning yellow.
In the event that the problem is serious, an affected grevillea can be sprayed with a fungicide designed for Australian native plants.
Root rot can be common if your grevillea is not growing in well-drained soil. These native plants don’t like sitting in waterlogged soils.
Root rot will first be noticed by the appearance of white fungus around the base of the plant.
Once a grevillea has been infected with root rot, it cannot be saved. It needs to be dug up and discarded.
It’s also important to note that some fungal spores can still be present in the soil so you should avoid planting in that spot until you’ve treated the area with fungicide.
To identify whether your grevillea has been infected with cinnamon fungus, you need to look closely at the leaves.
The leaves will generally turn yellow and wilt. You might also notice orange marks along the stems and the trunk of the plant.
Cinnamon fungus is common in soils will poor drainage and can be difficult to get rid of.
To avoid this problem, make sure your grevilleas are planted only in well draining soil. Water only the roots of the plant and avoid getting the foliage wet.
Sooty mould can be a common problem for grevilleas grown in humid areas.
Although the mould is quite unattractive, it will not harm the health of the plant.
To control sooty mould, you can trim away the infected areas and ensure that you only water at the root level.
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As you’re most likely aware, many Australian native plants are highly sensitive to an overabundance of phosphorus.
This is because most Australian soils are phosphorus-deficient and our native plants have adapted to live happily in low-phosphorus soils.
If your grevillea is suffering from phosphorus toxicity, it will exhibit burnt leaves. By the time this is noticeable, it’s usually too late to remedy the situation and the plant will likely die.
Phosphorus toxicity is one of the major causes of grevilleas dying. To avoid this problem, choose a fertiliser that is designed for Australian native plants and is low in phosphorus.
Grevillea looper caterpillar
The grevillea looper caterpillar can cause major damage to your plants. In fact, in severe cases, it can totally defoliate your gorgeous grevillea.
To get rid of them, spray your plant with an effective insecticide designed specifically for Australian natives.
Be vigilant in checking your plant often and remove any offending caterpillars as soon as you spot them.
Grevilleas not flowering
If your grevilleas are not flowering, it usually means that they are not getting enough sunlight and that the soil is not well-drained. Grevilleas don’t do well in heavy clay soils.
To encourage your grevillea to flower, ensure that you tip prune them often to encourage new growth.
You should also fertilise them with a fertiliser that is low in phosphorus and designed specifically for Australian native plants.
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What is wrong with my Grevillea?
Common grevillea problems include fungal diseases, phosphorus toxicity due to over fertilising with phosphorus, and damage caused by the grevillea looper caterpillar.
What causes yellow leaves on Grevillea?
Yellow leaves on grevillea are often caused by Phyllosticta fungus which causes leaf spot or Cinnamon fungus which causes leaves to turn yellow and wilt. With Cinnamon fungus, you may also notice orange marks along the stems and the trunk of the plant.