Gardeners who spray their roses with a common fungicide could be harming bees.
A chemical used to protect roses from black rot and powdery mildew damages bees' muscles.
Myclobutanil is recommended by the Royal Horticultural Society to stop the powdery mildew which affects ornamental plants. In roses it forms a white fungal growth, causing flower buds to fail to open.
But the popular fungicide has been found to react badly with a naturally-occurring chemical in plants which bees ingest. Scientists at the University of Illinois found the substance damages the thoracic muscle honeybees need to sustain lengthy flights and which they vibrate to generate heat of up to 35C to keep warm in winter.
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Myclobutanil, also used by farmers, was found to put bees ‘at risk of being unable to extract sufficient energy from their natural food’, Proceedings of the National Academy of Sciences journal reports.
Dr Ivor Davis, former president of the British Beekeepers Association, said: ‘We would like to encourage more gardeners not to use pesticides and fungicides unless they are absolutely sure they are bee-friendly.’
Dr Richard Comont, science manager at the Bumblebee Conservation Trust, said: ‘This study demonstrates the potential harm which can result from using even apparently innocuous chemicals on our gardens.’