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How to treat grevillea plants with black markings on leaves?

Hi I have 3 different grevillea plants around 1 year old

that have potential fungal issues. They are all in pots in full sun in native Potting mix with chip bark mulch. Up until winter they were sitting close together. 1 has red rust underneath leaves, I has grey crispy leaf tips that spread to the whole leaf and

die off and the other has black markings all over the leaves that completely go black or orange. Could these have a fungus? I have tried the liquid copper solution twice as foliar application and removed affected leaves but no results yet. They are still growing and flowering but getting more discolouration. I have a feeling it's fungus as last summer I used to top water and didn't let them dry out between watering.

Any help would be great.

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Comments

JacobZ

Hi @ashjell,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

It sounds like your grevilleas may indeed be experiencing fungal issues, likely exacerbated by your previous top-watering practices. Each of the symptoms—red rust, grey crispy leaf tips, and black markings—points to different potential fungal infections. Here's a breakdown of what might be happening:

Red rust under the leaves is likely due to a rust fungus, which is common in grevilleas. The copper-based fungicide should help, but it may need more frequent applications. Be sure to follow the recommended intervals on the product and keep up with it for a longer period.

Grey crispy leaf tips leading to whole leaf die-off could be due to a root issue. Ensure that the pots have proper drainage, and avoid overwatering, especially in cooler months.

Black markings that turn orange or black on the leaves could point to Phytophthora or another fungal pathogen. If the copper spray isn't working, you might need a systemic fungicide that targets root-borne diseases such as Yates Anti Rot Fungicide.

Since they're still growing and flowering, your plants are likely fighting the infection, but additional measures could help. Consider the following:

Improve air circulation by spacing out the pots more.
Switch to bottom watering if you're still top watering to avoid getting the foliage wet.
Check drainage in the pots. Waterlogged roots can increase fungal problems.

Lastly, ensure they dry out between waterings to prevent further fungal growth.

Allow me to tag @Noelle to see if she has any thoughts.

You might also like to have a read of this Grevillea Planting, Growing & Pruning Guide.

Let me know if you have any other questions.

Jacob

Noelle

@ashjell

Jacob is right on the money with his diagnoses of your grevillea issues, and he's given you the best possible advice. With appropriate action, they hopefully will recover/recuperate and thrive.

ashjell

https://www.workshop.bunnings.com.au/discussion/comment/43357#Comment_43357

Thank you so much for your advice. I'm glad to hear there is still hope. I will definitely continue with the copper as suggested.

ashjell

https://www.workshop.bunnings.com.au/discussion/comment/43362#Comment_43362

Thank you. I will definitely follow Jacobs advice.

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