Sally Smith on courgettes, ants and blackfly
Organic gardener Sally Smith answers your questions about why courgette leaves may turn silver and how to treat blackfly. If you have a similar problem with your courgettes,Ìýshare your experiences in the comment section below.
Louise from Newcastle asks: The older leaves of my courgettes have turned silver in colour. I have had a number of courgettes which are tasty but now they are going soft before they are large enough to harvest and are covered in what appear to be black eggs with ants running all over them. I water nightly when needed and feed once a week.
Answer: It is normal for courgettes to develop silvering of the older leaves, this isn't anything to worry about so long as the leaves are otherwise healthy in appearance. If they develop a white powdery coating, this is a fungal disease called powdery mildew and I don't think this is what you are describing.
I suspect the other problem that you describe is blackfly and that they are being 'farmed' by ants.
If you examine the black dots closely you will find they are tiny black aphids and are producing sweet honeydew from feeding on the sap of your courgettes. The honeydew is what attracts the ants and they protect the aphids from predators that would normally help to clear the problem. These pests may or may not be contributing to the formation of poor fruits. I would start by removing the worst affected fruits and then inspect any new ones daily for re-infestations. To keep these clear simply rub off the insects gently or use a jet of water to remove them.
Unless your courgettes are growing in grow bags or pots, I would advise to stop liquid feeding the plants as overfeeding will encourage too much leafy growth that in turn is attractive to pests such as the aphids.
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