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How to treat black spots on leaves?

Hi everyone,

This tree in my backyard was subjected to a lot of pruning recently and now its leaves have started to show black spots.

Not sure if it's due to (1) the pruning, (2) lots of rain in Adelaide, (3) bacterial or fungal infection, (4) ants?

Please tell me what I should do to save this tree -- it has beautiful tiny purple flowers in summer.

Help with identification of the tree would be much appreciated too!

Here's the whole tree. You can see where the top was cut off a couple of months ago.

black spots on the leaves

Black spots with white centres

lots of ants on the tree

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Comments

MitchellMc

Hi @bergamotblack,

I'd like to say it's sooty mould, but doesn't look right with those splotchy areas. Sooty mould is created by sap-sucking insects like scale, mealybugs, aphids and mites. They produce a sugary substance called honeydew, which the sooty mould grows off. The presence of ants supports this theory as they are often found feeding on the sweet honeydew. Regardless of it not fitting the ID of sooty mould, there's no harm in spraying Eco-oil on the plant, in case these insects are present.

I'm fairly sure this is more likely a fungal infection, or stress damage from the recent prune. Once again, applying a fungicide, removing and disposing of heavily affected and dropped leaves, and ensuring your plant has adequate drainage wouldn't hurt.

I believe the plant is Golden Dewdrops (Duranta erecta). Does it have purple flowers?

Let me tag one of our knowledgeable gardeners, @Noelle, to get her thoughts.

Please let me know if you have any questions.

Mitchell

Noelle

Hi @bergamotblack & @MitchellMc

This looks very like black spot fungus, the same disease that affects roses and a host of other shrubs too. It starts off with a small black area which then turns brown as the tissue in the centre of each spot dies. It can spread quite rapidly if not controlled.

The treatment suggested by Mitchell is the right way to go. It is important to prune off affected areas and pick up all infected leaves that have fallen to prevent recurrent outbreaks.

bergamotblack

https://www.workshop.bunnings.com.au/discussion/comment/40875#Comment_40875

Yes, it does have purple flowers. We have purchased an organic fungicide as there is an orange tree next to it. Thank you for your advice!

bergamotblack

https://www.workshop.bunnings.com.au/discussion/comment/40876#Comment_40876

It is definitely rapidly spreading to the clover on the ground beneath it. We have removed all the infected clover and the worse of the tree leaves before applying a fungicide. Thank you for your advice!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/82680#Comment_82680

Keep us updated, @bergamotblack, and reach out if you don't see improvement. We're here to help.

Mitchell

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