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
