Fireblight, a bacterial disease that destroys trees and is highly contagious, was first discovered in the Bayside area of Dublin last month and has since spread to more than 20 trees in the area.

"If the disease were to become established in Ireland, particularly on hawthorn, it would be catastrophic, " said Gerry Fitzgerald, senior executive parks superintendent with Fingal County Council.

"Plants with the disease must be removed immediately and destroyed by burying or burning."

Fireblight arrived in Ireland in 1986 but has never become established here. Trees such as apple, pear, hawthorn, whitethorn and mountain ash are particularly susceptible and it can cause great damage to fruit crops.

According to Dr Helen Grogan, plant pathologist with Teagasc, fireblight is spread from tree to tree by bacteria that is picked up by insects or spread by rain splashes. It is thought the inordinately wet summer has probably led to more trees being infected.

"Bacteria oozes from infected trees and when it is dry, it's not so bad, " she said. "However, when it rains, the bacteria spreads from tree to tree, so the recent wet weather has probably not helped matters."

Fireblight symptoms include wilting and death of flowers and young shoots before infection spreads to the branches.

The most obvious sign of the disease is the 'shepherd's crook', when branches become bent and shrivelled. The tree can almost never be saved once the disease has taken hold.

Since last month, six trees in Bayside have been felled and another 16 are due to be cut down in the coming weeks.

"Fingal County Council, working in conjunction with the Department of Agriculture, is taking the required actions to deal with trees suspected of fireblight infection in the Bayside area, " said a council spokeswoman. "We will be replacing any of the removed trees with fireblight-resistant species as soon as it is practical to do so."

Meanwhile, a new study from Teagasc has found that elm trees around the country are in danger of being killed off altogether by dutch elm disease, a fungus which is carried by a leaf-eating beetle.

The report by Dr Gerry Douglas, principal research officer at Teagasc's Kinsealy research centre, found that only a small number of healthy trees are left in Ireland and a plan has been put in place to plant more elms which may have a better resistance to the disease.