Hundreds of horse chestnut trees across Oxfordshire are under threat in what looks to be the worst case of tree blight since Dutch elm disease 30 years ago.

The outbreak follows the arrival in the county two years ago of the horse chestnut leaf-mining moth.

An infestation of the insects this summer has left trees in poor health, with leaves withering long before the onset of autumn.

And there is bad news for children, with the blight significantly reducing the number of conkers produced.

Oxford City Council tree officer Michael Lear believes 1,000 trees may have been affected in Oxford alone.

It is still unclear what the long-term impact of the moths, which originate in the Balkans, will be. They were first spotted in the UK in Wimbledon, London, and were found in North Oxford two years ago.

At the moment there is nothing to control the moth or stop its spread, say experts.

Mr Lear said although there was no firm evidence to suggest that horse chestnuts would die, the repeated defoliation was bound to seriously undermine the health of the trees.

To make matters worse, some horse chestnuts are also being ravaged by a bleeding canker.

City council tree expert Kevin Calidcott said: "The advice is that tree owners should not rush out and fell their horse chestnut trees because of the problem.

"In the meantime, the council will be carefully monitoring the condition of trees in its ownership."

Mari Girling, chairman of the Iffley Fields Residents' Association, said: "The infestation is having a very marked effect on horse chestnuts in the city, which have very few conkers this year. It's important that people realise that trees don't have to be felled, especially since there are so many in schools."

A spokesman for Forest Research, the scientific arm of the Forestry Commission, said: "Collecting up and disposing of the leaves in autumn is a way of trying to keep the trees looking good for longer.

"These leaves contain the over-wintering stage of the moth, the pupae, and their removal can delay the onset of the damage to the leaves the following spring." Leaves should be burned or, if composted, covered with a 10cm layer of soil.

Forest Research said it was now trying to find ways of using natural enemies to bring the moth under control.

For more information, see www.forestresearch.gov.uk