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 trees have been hit by the arrival in the region of the horse chestnut leaf-mining moth.

The infestation has left trees looking in poor health, with leaves withering long before the onset of autumn. And there is bad news for the county's school children, with the blight significantly reducing the number of conkers produced.

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

It is still unclear what will be the long-term impact of the moths, first established in the UK in Wimbledon four years ago. At the moment there is nothing to control the moth or stop its spread, say experts.

Heavy infestation results in leaves turning brown and dropping, with the tree taking on an early autumnal appearance.

Mr Lear said although there was no firm evidence to suggest that horse chestnuts would die, the repeated loss of three-month growth and repeated defoliation was bound to seriously undermine tree health. To make matters worse it seems that some local horse chestnuts are also being affected by a bleeding canker.

The arrival of the moth in Oxford has been reported to the Forestry Commission.

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."

The horse chestnut leaf mining moth was first observed in Macedonia, in northern Greece, in the late 1970s.

Forestry Research says it is now trying to find ways of using natural enemies and parasites to bring the moth numbers under control. But a spokesman added: "This could take some time."