THREATS FROM ABROADSudden Oak Death

THREATS FROM ABROAD
Sudden Oak Death
Last year’s report on Pests and Diseases (Evans and Webber, 2002) described the risk posed by a new fungal pathogen, Phytophthora ramorum. This is currently the cause of widespread mortality of oaks in coastal areas of California, USA, and the rapid onset of symptoms frequently seen in infected trees has led to the disease name ‘Sudden Oak Death’ or SOD. The same fungus has also been found sporadically in the Netherlands and Germany where it causes a twig blight of rhododendron and has also been found killing nursery plants of viburnums and rhododendron (Werres et al., 2001).
In June 2001 an information leaflet was prepared describing the symptoms caused by SOD on oaks in California, and the possible symptoms that might be seen if UK oaks were infected. Over 2000 copies of this Exotic Pest Alert were circulated to arborists, tree officers and foresters. As British oaks are already subject to a widespread but low level mortality and dieback known as ‘oak decline’ (caused by a complex of root infecting fungi, recurrent droughts and insect defoliation), there was concern that decline symptoms could be masking the somewhat similar symptoms of SOD. To assess whether P. ramorum could be infecting oaks in Britain a range of oak decline sites were resurveyed for any signs of SOD, with particular attention given to sites where rhodendron was a component of the surrounding vegetation. However, no evidence of the disease was obtained, and all visible symptoms could be attributed to known problems of oak dieback. To evaluate in more detail the risk that SOD might pose to oaks (and possibly other trees species) in the UK, pathogenicity tests were undertaken with P. ramorum under licence in high security quarantine containment chambers. Freshly felled logs cut from a range of broadleaved species, but with particular emphasis on Quercus species, were inoculated with isolates of P. ramorum obtained from Europe and California. After a few weeks the extent of lesion development in the bark and sapwood around the inoculation point was taken as an indicator of pathogenicity (see Plate 1 (a), (b) and (c)). The results of these tests were promising in that Quercus robur appeared relatively resistant to the fungus and only small, limited lesions developed. However, Q. rubra (American red oak) and Fagus sylvatica (European beech) showed signs of greater susceptibility to P. ramorum and further tests are planned. Closer study of the pathogen has also revealed that it has two mating types (A1 and A2), with the A2 only apparently present in the USA and the A1 in Europe. This raises questions about the geographic origin of this new pathogen and its potential for genetic change through sexual recombination. More information about this research is available on the Forest Research website or from one of the authors (joan.webber@forestry.gsi.gov.uk).
Coleoptera intercepted in port inspections and in pheromone traps
As part of the service that Entomology Branch provides for the Forestry Commission Plant Health Service, rapid identification is carried out of insects intercepted during port inspections and which are captured in pheromone traps at ports and timber yards. There were relatively few significant interceptions during 2001 but among the list are Coleoptera of high quarantine significance (Table 1).

Tabel 1

The eight-toothed European spruce bark beetle, Ips typographus, has been regularly intercepted and poses one of the most serious threats to spruce forests in this country. It was found during regular inspections by Plant Health Service staff and in pheromone traps at five different locations. Among the other bark beetles, several are already present in Britain but their interception indicates that there were infringements to the quarantine requirement that all bark should be removed from sawn timber. Two species of Ips from North America were also intercepted. Although neither species is regarded as a serious pest in the country of origin, their potential impacts in new locations may be less predictable. For example, I. grandicollis has established in Australia (Berisford and Dahlsten, 1989) where it has caused significant damage to radiata pine (Pinus radiata).