- Distribution and susceptible species
- How it spreads
- Report sightings
Cedars are non-native evergreen conifers that have been used as ornamental trees in gardens and estates in Britain. More recently, cedars have been considered as an alternative forestry species, particularly on drier sites in southern and eastern Britain. Cedars are generally pest and disease-free, but in 2014 and 2015 Atlas cedars (C. atlantica) were observed with severe shoot blight and defoliation. The fungus Sirococcus tsugae was identified as being consistently associated with these symptoms.
Until recently S. tsugae was only recorded in western North America, where it occurs on two species of Tsuga and Cedrus. Sirococcus shoot blight of western hemlock was originally described from British Columbia and Alaska, with specimens now known to belong to S. tsugae having been collected on Tsuga as early as 1966.
Sirococcus tsugae has been confirmed from the Pacific Northwest as well as the Northeastern and Southeastern United States on cedars (Cedrus Atlantica and C. deodara) and hemlocks (Tsuga heterophylla and T. mertensiana). Recently, it has also been detected on Eastern hemlock (T. canadensis) in Georgia, USA. It is reported that S. tsugae appears to be less aggressive on T. canadensis than on T. heterophylla.
In 2014, the pathogen was reported on C. atlantica in Germany (EPPO Reporting Service 2015 no.4).
S. tsugae has been detected at several locations in England, Scotland and Wales since the first report on C. atlantica in England.
It has also been confirmed as being present on a herbarium specimen of T. mertensiana collected in Scotland in 2004, and on young T. heterophylla regeneration in south-west England.
The conidia (asexual, non-motile spores) of the fungus are locally dispersed by rain splash, and it is probable that strong winds can disperse them over longer distances. Seed transmission has been reported for S. conigenus, but we have no information about the potential for transmission of S. tsugae via seeds. Planting stock, and possibly also cut foliage and seeds of Cedrus and Tsuga species from countries where S. tsugae occurs, are pathways for spread.
Cedrus has needles arranged spirally on the young leading shoots, and in whorls on short spur-like side-shoots. In the spring, affected trees display dead needles on the shoots, dead shoots (Figure 1- below left), cankers (Figure 2- below right) and gum exudation.
The dead needles are very distinctive because they have a characteristic ‘pink’ colour (Figure 3- below left), and only become brown as the season progresses. The fruiting bodies of S. tsugae might be observed on the dead needles (Figure 4- below right).
Affected branches can display cankers, but these are often indistinct and characterised by a slight reduction in branch diameter, together with a change of bark colour from green to a darker red / purple (Figure 5- below left). Resin bleeding from the bark can also accompany these symptoms in some cases (Figure 6 - below right).
The fruiting bodies of S. tsugae might be seen on the surfaces of cankers during the winter months and into the spring (Figure 7 - below left). Branches can die if they are girdled (Figure 8 - below right).
Brown lesions are evident in the phloem tissue of the bark (Figure 9 - below left), and might extend from affected shoots into the subtending branches and the main stem, where they can spread longitudinally (Figure 10 - below right).
On western hemlock (T. heterophylla) the disease is especially apparent in natural stands on advanced regeneration in the understorey (Figure 11 - below, upper left). It can affect one or many shoot tips on a single tree (Figure 12/14 - below, upper right and lower right). On T. mertensiana the fungus causes shoot blight (Figure 13 - below, lower left).
Cedrus and Tsuga species are valuable ornamental and forestry species in the UK. Although much uncertainty remains concerning the geographical distribution, biology and potential impact S. tsugae in Britain, it might cause significant damage to valuable ornamental trees in public and private gardens and economic losses, in particular for the nursery sector.
No effective control measures against S. tsugae in forest stands have been reported from North America to date, and information about possible control methods in nurseries or in parks and gardens is scarce, and mainly promotes hygiene methods.
Sirococcus tsugae is not currently listed in the European Union’s Plant Health Directive. However, its addition to the Alert List of the European & Mediterranean Plant Protection Organization (EPPO) is under consideration.
If you think you have spotted signs of Sirococcus tsugae, please check the symptoms section above before reporting it.
For more information on the science and research visit the Forest Reseach website.