Killer tree blight alert for Irish forest owners
Already, the forest service in Britain has felled 5,000 acres of trees in an effort to halt the rapid spread of Phytophthora ramorum, since the August 2009 finding of the disease in Japanese larch throughout Britain and in Northern Ireland — the first time it had been found infecting a commercially important conifer anywhere in the world.
Previously, a different strain of Phytophthora ramorum had killed millions of North American oaks, giving rise to its common name of “sudden oak death”. Native oaks have been little affected in Britain and Ireland, where the term “Ramorum disease” is preferred.
The British forestry industry is likely to cease planting Japanese larch in some areas, and warns the disease can spread to previously unaffected plant species, and poses a major challenge to control.
Following the first detections in Ireland in July 2010, further surveys have confirmed the disease in Japanese larch at 11 forest locations in five counties, where more than 300 acres of forest have been felled as a disease control measure. However, most of the wood from infected trees can be utilised and sold in the normal way, if prescribed hygiene measures are taken during felling, transport and processing.
There has also been a recent scientifically confirmed finding here in a single Sitka spruce, growing in close proximity and underneath the canopy of a large infected rhododendron, which is the plant species most commonly infected in Ireland. The Forest Service of the Department of Agriculture has asked forest owners to be vigilant for symptoms of ill health in larch or other species.
Phytophthora ramorum, which is related to the Phytophthora infestans which caused the Irish potato blight and Great Famine, can kill Japanese larch trees in one growing season after its presence is first detectable.
Like potato blight, it thrives in damp environments. Infected Japanese larch produces particularly high numbers of the inoculum that spreads the disease, which can quickly spread to a large number of trees and shrubs in mists, rain and air currents. Hence, the most effective means of preventing the spread is to fell infected trees and plants, in order to remove the living plant material on which the pathogen depends.
No cure has been found, so the control objective is to minimise spread. Infected trees should be felled as quickly as possible.
Along with the wider threat posed to the forest industry, the experience in Britain has been that a greater than usual volume of larch logs entering the timber market has depressed prices. Well known for use in fencing, larch also substitutes for spruce in sawmills, and is used for decking and other garden products, and for exterior building cladding.
The symptoms of Phytophthora ramorum infection in larch include excessive resin bleeding, sunken or cankered areas of bark, wilting of the needles with the tree canopy turning grey, and branch and shoot dieback with a distinctive ginger colour.
