Plant Doctor Archive

Black spots on swan plant

I have a swan plant growing outdoors, and towards the end of summer, as the monarchs were leaving, I noticed the leaves of the plant were covered in black spots and were also present on the stems too. I'm confident in labelling this a fungal infection and would like to know more about what fungus it is and how to treat it.

I am wondering if the black spots you describe are black aphids which do look different from the common green aphid. Being on a swan plant, they are best removed by fingers or soapy water rather than spraying, as there may be monarch butterflies flying around on sunny days and an insecticide spray will kill them.

If you are unsure, take a sample into your local garden centre for positive identification before taking action.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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