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An organic way to treat white flies on French beans

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Sally Smith Sally Smith | 11:02 UK time, Friday, 13 August 2010

Organic gardener Sally Smith answers your questions about white flies on French beans. If you have a similar problem with your French beans, share your experiences in the comment section below.

Lesley Hardy from Kings Lynn asks: I have lots of little white flies on my French beans. Are they anything to do with white butterflies as there seem to be lots about? I am spraying them with washing-up liquid. Is that OK as I don't like using chemicals?

Answer: The flies are not related to white butterflies, these are cabbage white butterflies and are a specific pest of plants in the cabbage family, they will not therefore harm your beans. I wonder too if the flies that you see are actually damaging the bean plants or whether you are spraying unnecessarily? The first 'rule' of treating a problem is to first identify it accurately otherwise we are in danger of killing creatures needlessly that are doing no harm and may indeed be beneficial creatures that are predators of pest species!

That said, there is a pest actually called 'whitefly', it is a tiny white fly, 2mm to 3mm long, usually clouds of them fly up when plants are disturbed though they mostly infest cabbages and not beans.

My advice would be first of all to stop spraying altogether and definitely do not use washing up liquid as it is not suitable to be used on plants and is not particularly effective at clearing up pest problems. Observe the plants regularly for actual damage - such as leaves turning yellow, developing black mould on the upper surfaces (sooty mould) and seeing flies and their young (they look like tiny scales) feeding on the undersides of the leaves. If these symptoms are present, treat as for whitefly with an insecticidal soap spray based on fatty acids. Spray in the evening to avoid beneficial insects such as bees and target the undersides of the leaves where the flies are found, always follow the manufacturers instructions for spraying.

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