Infected larch can clearly be seen in this picture.

A DEADLY contagious disease related to the potato blight that caused the great famine is threatening trees across West Cork.

 

The Phytophthora ramorum fungus is a soil borne plant pathogen that causes root disease in Yew and Chamaecyparis conifer trees and hedges; the most frequent symptoms of the disease are root and collar lesions.

 

Two strains of the disease have been confirmed here affecting Japanese Larch and Rhododendrons.

 

It is believed to have come into Ireland through contaminated soil in root ball conifers imported from Holland to be used in the horticulture sector for amenity gardens and parks.

 

It can persist in soil for years, even after infected plants have been removed, to infect a wide range of trees and other plant types.

 

 

Infected trees become infected when their roots come into contact with the zoospores in soil or water.

 

The foliage of infected trees initially appears slightly lighter in colour than that of healthy trees.

 

Sections or the whole canopy can turn olive grey then brown when the tree is dying.

 

 

Local horticulturalist John O’Reardon said, “The disease is very infectious to the conifer group and some other trees, but harmless to people, animals and most other plants.

 

“It can persist in soil for years, even after infected plants have been removed, to infect a wide range of trees and other plant types.

 

“Eradication is still the aim, but the omens are not good; burning or deep burial of dying trees help implement bio security measures to minimise the risk of spreading the disease.

 

“The disease can be transmitted in soil, on footwear and via pruning and cutting tools.”

 

 

Since Phytophthora ramorum was first detected in Ireland in Japanese Larch in Tipperary in 2010, ground and aerial surveys have continued.

 

During 2011 the disease was detected in Japanese larch at two new locations, one in Cork and one in Wicklow.

 

 

During 2011 further additional outbreaks were also detected adjoining previous infected sites at three of the 12 locations where the first findings were made in 2010: Cork, two adjoining outbreaks; Tipperary, 11 adjoining outbreaks and Wicklow, one adjoining outbreak.

 

 

An aerial survey was carried out during July and August and completed in mid August.

 

The extensive survey was carried out with the assistance of the Irish Air Corps and 190 waypoints of larch forest of varying age classes covering a broad geographical spread of the country were visually assessed by the Forest Service.

 

Larch and general forest health was also assessed while flying between the waypoints. Suspect sites identified from aerial surveillance are currently being followed up with ground surveys.

 

 

To date there have been no further new findings but extension of infection in a number of previously infected areas is suspected.

 

In following up some of the suspect sites on the ground, symptoms not typical of P. ramorum have also been observed and these are likely to be caused by a non-quarantine needle cast disease.

 

 

In rhododendrons, outbreaks, P. ramorum has been detected in 2012 on wild rhododendron at one new forest location in Tipperary and in two new locations in Waterford.

 

 

A number of other additional suspect sites have also been detected during the 2012 surveys.

 

 

Phytophthora ramorum infected Rhododendron.

To date the total number of confirmed locations of Phytophthora ramorum infection in Japanese larch stands is 14 accounting for findings in six counties, namely Cork, Wicklow, Kilkenny, Tipperary, Waterford, and Kerry.

 

 

All forests where the disease has been found are subject to strict quarantine controls and felling of the infected larch areas is required as part of the disease management strategy.

 

 

Timber from infected forests can be utilised and sold provided hygiene measures are taken and in this regard a number of processing facilities have been licensed to process infected timber.

 

 

The key challenges are to ensure that sanitation felling, haulage and processing of infected material is carried out in compliance with disposal notices issued by the Forest Service of the Department of Agriculture in order to prevent the further spread of the disease.

 

 

Forest owners are requested to be vigilant and to report any unusual symptoms of ill health in larch or other species to the Forest Service of the Department on 01 607 2651 or email forestprotection@agriculture.gov.ie.