September 2012. In an extensive article from the BBC, the UK faces an “unprecedented level of threat” from pests and diseases according to the Forestry Commission. The threat comes from non-native species, with those of greatest risk listed as follows:
- Phytophthora ramorum– fungal pathogen that infects the commercially important conifer species, Japanese larch
- Acute oak decline (AOD)– An aggressive bacterial disease that can kill an infected tree in just four or five years
- Great spruce bark beetle – breeds under the bark, weakening the infected tree and in extreme cases, can kill the tree
- Chalara dieback of ash– “a serious disease of ash trees”, caused by a fungus called Chalara fraxinea, and can kill an infected tree
- Horse chestnut bleeding canker– appears as an area of dying bark that oozes liquid. If it spreads around the entire trunk, it cuts off the food supply, killing the tree.
The plant trade is singled out as a major rick, with an “ever-widening diversity of plants and plant material being traded around the world”.
Later, October 2012, several articles appeared online concerning the so-called ash tree crisis. This is from the Guardian: http://www.guardian.co.uk/environment/2012/oct/30/ash-tree-crisis-dieback-disease.
80 m trees in the UK are vulnerable to ash dieback, Chalara fraxinea, a fungus that has swept across Europe and entered Britain. Entry has most probably occurred via imported saplings earlier this year. It seems that seed from the UK is collected and sent to Holland to be grown and then sent back as nursery plants. Infection starts on the leaves, then moves into the shoots and heart of the tree. Spores readily spread the fungus. In Denmark, 90% of the trees are showing symptoms, and it is widespread in Netherlands and Belgium. In February this year, it was discovered in imported plants in a nursery in Buckinghamshire.
A task force to combat the fungus has been formed and details of its work can be found here: http://blog.plantwise.org/2012/11/09/research-teams-and-scientists-working-to-stem-ash-dieback-fungus/. This account also gives information on CuPC33 which is being used as a fungicide against the fungus.
Between 1% and 2% of ash trees in Denmark are showing signs of immunity from the disease, so there is hope for the future.
As a member said: Why import ash seedlings from Europe (I think UK horticulture could easily manage to produce this indigenous species) especially when the disease problem is long known there, and Denmark’s ash trees are very badly affected. I cannot imagine what can now be done. Add Phytophthora ramorum to our bad experiences of importations.
Not connected with the above, but nevertheless interesting as it concerns Chestnut blight in the USA and what is being done, is an articles in Nature:http://www.nature.com/news/plant-science-the-chestnut-resurrection-1.11504.