Phytophthora ramorum symptoms on Japanese larch
The disease caused by the pathogen Phytophthora ramorum a fungus like organism, can damage and kill plants and trees it infects.

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

For more information and pictures of the disease:

How to identify Phytophthora ramorum:

Update on Phytophthora ramorum

  • Since Phytophthora ramorum was first detected in Japanese larch in 2010, ground and aerial surveys have continued. During 2011 the disease was detected in Japanese larch at 2 new locations, 1 in Co. Wicklow and 1 in Co. Cork. During 2011 further additional outbreaks were also detected adjoining previous infected sites at 3 of the 12 locations where the first findings were made in 2010: Co. Wicklow, 1 adjoining outbreak; Co. Tipperary, 11 adjoining outbreaks and Co. Cork, 2 adjoining outbreaks.
  • Ground surveys have continued during the 2012 season and with the assistance of the Irish Air Corps an extensive national 2012 aerial survey of larch was carried out. Any suspect sites from aerial surveillance are being subsequently followed up on the ground to determine the cause of the symptoms. To date in 2012 there have been no further new confirmed findings in Japanese larch but it will be later in the year before the overall 2012 P. ramorum situation can be fully assessed following completion of the national survey and laboratory analysis.
  • In relation to wild rhododendron outbreaks, P. ramorum has been detected in 2012 on wild rhododendron at 7 new forest locations. Rhododendron appears particularly symptomatic this year, probably related to the very wet summer. To date nationally wild rhododendron has now been found to be infected at 22 different forest locations. The non-compliant cutting and unauthorised removal of rhododendron for foliage production remains an ongoing serious disease management problem at several of the P. ramorum infected forest sites.
  • In summary to date the total number of confirmed locations of P. ramorum infection in Japanese larch forest is 14 accounting for findings in 6 counties, namely Wicklow, Kilkenny, Tipperary, Waterford, Cork and Kerry. This amounts to a total area of around 139 ha.
  • All larch 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. Most of the felling has been completed. 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 statutory Disposal Notices issued by the Forest Service of the Department 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. Telephone 01 6072651 or email This email address is being protected from spambots. You need JavaScript enabled to view it.

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