How to fix black spots on grevillea?

[nc]

I have two grevillea about a year old (moonlight and superb) and I have noticed that they have black patches. I have had a lot of rain lately and have clay soil. Is this something that I need to worry about? And if so, how do I fix it?

[EricL]

Hello @nc 

I believe you've got a bit of fungal infection happening. Is the soil damp and wet in that area all the time? Has the plant not had a chance to dry off? I suggest moving the mulch away from the base of the plant to allow the soil to breath and the moisture to evaporate. 

I recommend using Yates 200ml Liquid Copper Fungicide. It is a broad-spectrum fungicide, that is suitable for use on fruit, vegetables and ornamentals, for controlling leaf curl, leaf spots, blights, downy mildew and many more fungal diseases.

Please remember to wear personal protection such as appropriate clothing, gloves, goggles and a Citeco Half Face Respirator A1P2 Kit when spraying. Please make sure to follow all the safety guidelines printed at the back of the bottle.

Here is a handy guide: How to diagnose a sick plant by @Noelle 

If you have any other questions we can help with, please let us know.

Eric

[nc]

Thank you, yes, we have had a lot of rain lately so everything is damp. I will try the fungicide you recommend, thank you.

[HitOrMiss]

you can try and save it with a copper spray, but ultimately if the drainage is poor, it may just be a matter of a extended rain event.
your 2 varieties of grevillea dislike wet feet a bit more than other varieties.
regardless of what people may tell you, unless you physically remove the clay, there is no fast way to fix it.
you could try installing a drain but where would you run the water to ? it would likely be redirected somewhere else in your yard.

spraying copper will help with the signs of the fungal pathogen, but not necessarily the cause, which is likely the wet soil. 
adding a 'clay breaker' will likely change your soil ph, so you have to take that into account using those, and they take a very long time anyway if they do much at all.
you can also add worms and organic matter to help improve the soil, but that is a slow process aswell.
another thing you could do, is knowing the plant may be prone to the fungal disease in the environment it is in, spray preventatively instead of reactively. (do not just use copper repeatedly over and over and over, alternate it with something else, even a horticultural oil)

hopefully something mentioned helps. 

[JacobZ]

Hi @HitOrMiss,

Welcome to the Bunnings Workshop community.

Thank you for your advice, it's great to see you getting involved and it seems like you are very knowledgeable about plant and garden care.

Allow me to tag @nc, so they are notified of your response.

Jacob 

[nc]

Thank you for your advice