RAMORUM DISEASE: UPDATE

ISSUED JOINTLY BY DEFRA AND THE FORESTRY COMMISSION

Nine trees at three sites in Cornwall have now been found to be infected with Phytophthora ramorum, Defra and the Forestry Commission reported today. The trees affected are four holm-oaks, a turkey oak, two beech trees, one sweet chestnut and a horse chestnut. In the case of the sweet chestnut and the holm-oak trees, the damage was only on leaves. Recent cases, found on beech trees, a turkey oak and a horse chestnut, exhibit infected bark in the form of conspicuous “bleeding cankers”.

There are two other trees in Europe known to be infected – one in Sussex and one in the Netherlands. They are of two different American species of oak.

At one of the sites in Cornwall, a second new species of Phytophthora, which has not yet been identified, is causing disease on rhododendrons and a nearby beech tree. Defra and the Forestry Commission are assessing this new type of pathogen and whether the risk differs in any way from that posed by P. ramorum.

At the majority of the 300 other outbreaks in the UK, which have mostly been confined to rhododendrons in nurseries and garden centres, eradication has been achieved by immediate destruction of affected plants.

An intensive survey programme of retail outlets, nurseries, gardens and other established planting areas has been underway since the first finding was confirmed in April 2002. Precautionary eradication and containment action will continue, and surveillance will now be increased to reduce the risk of spread of this pathogen into the wider natural environment.

Buyers of host species - mainly rhododendrons, camellias and viburnum - are advised to check plants before purchase for symptoms of the disease and to contact their garden centres if these subsequently develop.

Ben Bradshaw, Plant Health and Forestry Minister, said:

“Defra and the Forestry Commission continue to monitor this situation very closely; the identification of a new type of disease is a matter of concern and we are working to establish the extent of the problem either this or the original disease type might cause to our tree population. That is why we are funding research to refine the risk assessment.

“We need to ensure the precautionary measures we are taking, including additional resources in surveillance and checking imports, are effective and proportionate to the risks.”


NOTES TO EDITORS

1. Defra and the Forestry Commission are considering, with local partner organisations, what further measures would assist in the containment of the disease, drawing on the best available scientific information.

2. On rhododendron, P. ramorum causes a twig and leaf blight. Affected twigs develop a brown to black discoloration that spreads along the twig and can move into the leaves. Characteristic symptoms include blackening of the petiole (leaf stalk), leaf base and leaf tip and may extend along the mid-rib. Twig cankers can lead to wilting of shoots; in such cases leaves remain attached but may not develop any spots. Leaf infection can also occur without twig infection. Roots are unaffected. Symptoms are similar to those caused by other Phytophthora species on rhododendron, but the development of symptoms is more rapid in P. ramorum.

3. On viburnum, infection commonly begins at the stem base causing wilting and ultimately death. It may also cause leaf symptoms similar to those on rhododendron.

4. On Pieris and Vaccinium, the pathogen causes brown stem lesions that lead to aerial dieback and leaf symptoms as described on rhododendron.

5. On Camellia, Kalmia, Syringa (lilac) and Leucothoe, the pathogen causes leaf blight with large brown to black lesions typically occurring at the tip or edges of the leaves. On Taxus (yew), P. ramorum causes a needle-blight affecting young foliage leading to an aerial dieback.

6. Further information on P. ramorum, including pictures and further descriptions of symptoms, can be found on the Defra and FC websites at www.defra.gov.uk/planth/oak.htm, and www.forestry.gov.uk/pramorum.

7. Surveys have been undertaken since 2001 when Forestry Commission scientists and experts in Netherlands and Germany identified a link between a new disease of rhododendrons on the continent and an epidemic which has been killing oak trees in coastal districts of California. After the first UK finding, on viburnums at a garden centre in April 2002, emergency measures were taken in the UK to prevent further spread. As a result of UK proposals these measures were extended to the whole of the EU later in the year.

8. The first finding of Phytophthora ramorum disease on a tree in the UK was described in a news release on 5th November, followed on 4th December by an announcement of further findings and additional resources to increase surveys for the disease, action against it, and research on the level of risk to UK trees.

Catriona Ross: 0131 314 6289
e-mail: catriona.ross@forestry.gsi.gov.uk