Image caption Symptoms of ash dieback include leaf loss and it can lead to tree death.

Ministers have said that 100,000 trees have been destroyed to try to prevent the spread of the deadly ash dieback disease.

A ban on the import of ash trees came into force on Monday and an expert tree disease taskforce has been established.

But Labour accused the government of being "asleep on the job" and failing to to act quickly enough.

Ministers said they acted as soon as the disease was confirmed and had taken the threat "extremely seriously".

The Chalara fraxinea fungus, which causes Chalara dieback - also known as ash dieback - has already infected 90% of ash trees in Denmark.

The disease was first spotted in the UK in February, at a nursery in Buckinghamshire, and was subsequently identified in other nurseries and newly planted areas.

But it has now been found in the wider countryside in East Anglia, sparking concerns the disease, which has the potential to devastate the UK's ash tree population, has spread to mature trees.

'Dither'

Environment minister David Heath told MPs that 100,000 ash trees had already been destroyed to try to prevent the spread of the disease - this is 42,000 more than the environment secretary had previously disclosed.

Mr Heath said: "On discovering Chalara in the UK, plant health authorities took immediate action to rapidly assess ash trees for signs of infection at over 1,000 sites where ash plants from Europe had been grown or planted in the last five years."

A voluntary moratorium on imports had been imposed before the government announced its temporary ban, he said.

Symptoms of Chalara dieback Diseased saplings typically display dead tops and side shoots.

Lesions often found at base of dead side shoots.

Lesions on branch or stem can cause wilting of foliage above.

Disease affects mature trees by killing off new growth. How to spot the signs

Shadow environment secretary Mary Creagh accused the government of "dithering" over the summer.

"Why did ministers sit back, cross their fingers and wait until the disease was found in the wild in June?" she asked.

Ms Creagh also attacked budget cuts for research into plant and tree health.

She said the Forestry Commission's budget had been cut by 25% and funding for research had been cut from £10m to £7m a year.

"Those cuts reduced the Forestry Commission's ability to identify and tackle tree disease," she said.

"After the forest sell-off fiasco, this incompetent government has been asleep on the job with ash dieback.

"Like Nero, ministers fiddled, and now it is our forests that will burn."

But Mr Heath denied there had been any cut back in resources: "There has been no reduction in the resources applied to plant health and tree health in this country."

Experts say that if the disease becomes established, then ash dieback could have a similar impact on the landscape as Dutch elm disease had in the 1970s.

This outbreak resulted in the death of most mature English elm by the 1980s. Elms have recovered to some extent but in some cases only through careful husbandry.

Visible symptoms of ash dieback include leaf loss and crown dieback in affected trees and it can lead to tree death.

The disease has been listed as a quarantine pathogen under national emergency measures and the Forestry Commission has produced guidance, including help on how people can identify possible signs of infection.

Mobile app

Experts are urging people to report suspected cases of dieback in order to prevent the spread of the disease to the wider environment becoming established.

An app, Ashtag, has been launched to try and map the spread of the disease by allowing users to upload pictures and report possible sightings to a team who will pass any information to the Forestry Commission.