TREE DISEASES: ROUND-UP

Photo: John May

Since my last post http://hqinfo.blogspot.co.uk/2012/07/ tree-news-sudden-oak-death.html in July this year, there have been a number of significant developments. This post is a round-up of issues and stories.

 

UK ACTION PLAN [UPDATE]

On 18th October 2011, the Government launched the Tree Health and Plant Biosecurity Action Plan which brings together DEFRA, the Forestry Commission, Forest Research, FERA and the Devolved Administrations to ‘set out a UK-wide integrated approach towards strengthening strategy for dealing with serious tree pests and diseases. The June 2012 Progress Report on the plan is available here. They are due to publish a further Progress Report before year end and have written to DEFRA for details. [DEFRA confirmed this is likely to be in November]

[Matthew Appleby, Deputy Editor of Horticulture Week was good enough to send me a copy of his article on the Action Plan (Pub. Sept 11th). As well as above, the partnership also includes the Biotechnology and Biological Sciences Research Council (BBSCR) with other research councils likely to be added. This coalition has been brought together under the Living With Environmental Change Partnership. Several million pounds over the next four years is being committed to the research effort.

 

OAK PROCESSIONARY MOTH

 

The Oak Processionary Moth (Thaumetopoea processionea) is native to central and southern Europe but spread northwards during the late 20thC. It was first recorded in the Netherlands in 1991 since when numbers have soared periodically. It  remains a major problem there and in neighbouring areas of Belgium, where 30,000 moths were recently caught in just one night. In Germany, police have sealed off infested areas and deployed helicopters fitted with sprayers to drench tree canopies with insecticide.

OPM arrived in Britain from Europe on imported trees in 2006 and has been defoliating trees in five west London boroughs: Ealing, Brent, Hounslow, Richmond-upon-Thames and Hammersmith and Fulham.

According to Amateur Gardening: ‘The Government has admitted that attempts to eradicate oak processionary moth (OPM) from streets, parks and gardens in London have failed. It has now spread as far afield as Reading and Sheffield.’

It is the caterpillars not only cause serious defoliation in  oak trees, their principal host, but are also a human health hazard. ‘Each 20-25mm bug is covered with 62,000 toxic hairs. The hairs easily penetrate clothes, causing skin irritation for up to a month.Other symptoms include vomiting, dizziness and fever.’ In France, there are reports of people being blinded. The caterpillar hairs remain toxic for up to five years and can contaminate nearby grass, soil and crops. Trees recover and leaf the following year.

Methods for controlling OPM caterpillars are: spraying trees with the controversial insecticide deltamethrin; using hair spray to glue the caterpillars together and then burning them with a blowtorch, using giant vacuum cleaners to hoover them up and then burning them in on-site incinerators; spraying trees with nematodes, a natural parasite.

Source: Amateur Gardening.

Forest Research provide advice and help. You must not attempt to handle the larvae caterpillars yourself, or disturb their nests.

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ASH DIE-BACK

Close up of the leaves and “keys” (fruit) of the common Ash.    Source: Wikipedia

Ash die-back is caused by a Hymenoscyphus pseudoalbidus), an anamorph ( an asexual reproductive stage) of the fungus Chalara fraxinea. This infects the tree’s leaf-stalks. When the leaves die and fall, they infect other trees. The fungus has destroyed 90% of Denmark’s ash trees and is causing serious problems in Germany, Poland, Norway, Sweden and Austria. Many European countries have been urging Britain to ban imports of ash saplings – an interim ban may come into force in November – but many feel its too late. According to Tracy McVeigh in The Observer:

‘In February, the fungus was found in a batch of trees sent from a Dutch nursery to Buckinghamshire. Between June and September it was confirmed in nurseries in Yorkshire, Surrey and Cambridgeshire, at a Forestry Commission Scotland woodland near Kilmacolm, and in ash trees planted in a Leicester car park. Conservationists hope it has not reached the 80 million ash trees in the wider British countryside, outside of new planting.

The UK and Ireland may well be, within the next 10 years, the only remaining places in Europe with ash. ‘

Full story here: www.guardian.co.uk/world/2012/oct/07/disease-killing-denmarks-ash-trees

There’s an exceptionally good post on this topic which explains a great deal more about this fungus, its life-cycle and the damage it causes. See: ‘Leaves, keys and Fungi’ on the Skeptical Squirrel blog.

 

HORSE CHESTNUT: BLEEDING CANKER

 

Bleeding canker on horse-chestnut tree. Map shows percentage of horse chestnut trees surveyed in 2007 with symptoms of bleeding canker. Source: Forestry Research

‘Horse Chestnuts have been prone to infection from pathogens from the genus Phytopthora for several decades, but infection rates which caused ill health remained at a relatively low level. However, for the last few years incidences of ill health in Horse Chestnuts have observed to be increasing at an alarming rate. Scientific research carried out on affected trees repeatedly confirmed the presence of a pathovar known as ‘Pseudomonas syringae pv aesculi’.

See full article: Farming Life [18th Oct 2012}

According to a 2007 report by Ian  Monger on the Arboricultural Information Exchange site:

‘In the UK the disease is now very widespread and the Forestry Commission estimate that up to 50,000 trees are affected, with probably a few thousand already felled.

The disease affects almost all ages of tree, from young trees with a DBH of only 10cm to mature specimen trees, including many highly visible trees in parks, gardens and avenues. The disease has struck the prominent double avenue of horse chestnuts leading to the prehistoric Avebury stone circle.

Research has shown about 50% of the horse chestnuts studied in Hampshire to be affected with bleeding canker (Straw and Green, unpublished data), with a higher proportion in amenity situations than in woodlands. Slightly more red horse chestnuts (A. x carnea) were affected than the white A. hippocastanum.’

[Unable to find any more recent statistics]