The Department of Agriculture, Food and the Marine (DAFM) is currently examining the option of providing support to forest owners with Japanese larch forests damaged by Phytophthora ramorum disease through a reconstitution scheme.
Phytophthora ramorum is a harmful pathogen which is known to have a wide range of hosts, including many tree species. The disease was first detected in Ireland in 2002 on imported Rhododendron and Viburnum plants.
In 2010, the disease was found to be infecting trees in Ireland, in particular Japanese larch (Larix kaempferi), and has since been recognised as a “serious threat” as it can cause damage and death of Japanese larch, the DAFM said.
At the start of 2022, the disease had been confirmed present in Japanese larch at 56 forest locations, affecting approximately 337ha. However, it is recognised that a “much greater area” has been impacted, the DAFM said.
Japanese larch
Phytophthora ramorum disease was first noticed in the early 1990s in plant nurseries in Europe and in forests in California. After being detected in imports into Ireland in 2002, the disease was detected in the wild in 2003 on Rhododendron ponticum.
Larch species across Ireland cover approximately 24,000ha, mostly in mixture with Sitka spruce. This represents about 3.3% of the total forest area in the country, according to the 2022 National Forest Inventory.
Larch plantations are distributed throughout Ireland, with larger areas planted in Wicklow, Tipperary, and Cork. The species of larch planted are European larch, hybrid larch and Japanese larch, with the latter being the most common.
The majority of the larch in Ireland occurs in mixed species stands and a smaller amount, approximately 4,750ha, in pure larch stands, according to the DAFM.
Because of the level of damage to Japanese larch, the DAFM ceased grant aiding Japanese larch and Hybrid larch in November 2010, the DAFM said.
Identification of Phytophthora ramorum
Symptoms at a forest landscape level:
- Dead and dying partially flushed trees in groups or scattered throughout the stand;
- Canopy may be an abnormal grey/brown colour;
- Affected trees may show needle wilt, branch and shoot dieback, abnormal shoot growth.
Symptoms at stand level:
- Partial or whole crown discolouration, (reddish brown or grey brown depending on level and stage of infection);
- Crown partially flushed (in needle) or not at all;
- Crown dieback;
- Excessive external resin bleeding in upper crown areas.
Individual trees:
- Wilt and dieback of fresh needles with blackening of needles;
- Shoot dieback from tip back along shoot;
- Resin bleeding on branches and trunk;
- Excessive side shoot/epicormic growth and heavy cone production may be observed.
Since 2010, the Forestry Inspectorate has worked with Coillte, as the principal landowner affected, in undertaking sanitation felling of infected larch in an effort to limit the spread, according to the DAFM.
Reconstitution
A reconstitution scheme is outlined in the Forestry Programme 2023-2027, and provides for supporting the restoration of forest potential arising from damage by natural events.
Reconstitution will be aimed at forests where significant damage has occurred. This means death or irremediable damage of 20% or more of the trees in the relevant plantation covered by the one contract number or forest block.
It will also include the removal of host species for diseases such as Rhododendro in the spread of Phytophthora ramorum. Infected material or host species will be removed where required and replanted where appropriate, the programme states.