East Anglia: Ash Dieback and other tree diseases one year on
PUBLISHED: 16:02 13 October 2013
Mike Seville, forest and woodlands adviser at the Country Land and Business Association, with an update on some of the devastating new diseases stalking our forests
The recent ban on the import of sweet chestnuts in the hope of saving Britain from the devastating blight which attacks their bark is a deadly reminder of the vulnerability of so many of our native trees.
It could not have come too soon, for though the widespread pests, conditions and diseases affecting ash, oak, pine, horse chestnut and larch might have disappeared from the headlines they are still here, still causing untold damage – and spreading to ever wider areas. Thankfully the chestnut import ban imposed by Owen Paterson, Secretary of State at Defra following pressure from us and the Horticultural Trades Association, is evidence that the situation is being taken very seriously by the government - as is the £8 million funding allocated to enable researchers to learn more about these killers and, it is greatly to be hoped, how to combat or, failing that, control them.
They and the trees they affect are: chalara fraxinea (ash dieback), acute oak decline, red band needle blight (pines) horse chestnut blight and leaf miner, and phytophthora ramorum, (larch). A year ago the public was made aware of chalara and its potential to deprive the country of its ash in the way that elms disappeared in the seventies.
So where are we now?
Chalara fraxinea. Twelve months of investigation has shown it is widespread in the wider environment and present in recent plantings across the whole of the UK. Both woodland and roadside trees of all ages are affected. What’s more it has certainly been here for at least five years - in some cases infected plants must have been brought into the country as long ago as 1996. This evidence, that by the time it was identified chalara was already established supports the conclusions of the Chalara Management Plan, in which the CLA played a crucial role: that the disease would be impossible to eradicate and efforts should be concentrated on the management of the trees as they became sick and in trying to identify and breed from any resistant ones.
There have already been two significant developments originating from Norfolk, both of which will be invaluable in managing the diseased trees and perpetuating ash in the countryside into the future. Firstly, scientists at the John Innes Institute have successfully mapped the genome of a strain from Denmark, which is believed to be resistant. Secondly an enterprising woodland owner has established a completely new market for good quality ash to China and Vietnam. This gives optimism for future sales, which in turn would make the necessary management more viable.
A third move is an initiative from the University of East Anglia in which the public is asked to help scientists identify and monitor healthy and diseased ash*. Forest Research has a similar project recruiting volunteers to monitor all trees ObservaTREE*
Acute Oak Decline (AOD). This destructive ‘disease’, usually an unholy alliance of bacteria and the agrilus beetle is definitely still with us and while there has been no large scale survey, forestry agents will tell you that it is continuing to attack more trees and expand its range. It has been found from Norfolk to Herefordshire. Many trees are dying, especially those with a heavy agrilus infestation but some, notably those with only bacterial bleeds or few beetles present do seem to be able to survive the attack - at least for now.
Horse chestnut blight and leaf miner. Early in the year it looked as if the long cold winter may have killed off many of the leaf miner moths whose larvae are responsible for the premature browning of leaves. Unfortunately that optimism has proved to be misplaced for although the symptoms appeared later than usual, most trees are now showing the dry, crispy brown leaves characteristic of leaf miner infestation and a steady stream of trees continues to die from the blight with its distinctive weeping black lesions.
Red band needle blight is a fungal disease that kills the needles of pine trees, dramatically reducing their growth and often resulting in their death. Predominantly a disease of woodland trees it was first identified in Corsican pines in Thetford Forest on the Suffolk/Norfolk borders. It is now also found in both Scots and Lodgepole pine throughout England and is rapidly spreading into Scotland. It thrives in the moist atmosphere of under-thinned crops and so heavy thinning has had some success in reducing its effects. However the last year has been a good one for the fungus and many pine plantations are looking very poorly indeed.
Phytophthora ramorum is another fungal disease which is currently killing thousands of hectares of larch trees in the west of England, Wales, and Scotland. Fortunately it has not yet reached the Eastern counties, but it is doubtless only a matter of time.
What can we do?
Unfortunately the reality is that there is no cure for most of these killers so we will have to learn to live with them. Some of them such as chalara will change the look of our countryside for decades – if not for ever - whilst others, such as AOD, will probably kill some trees but eventually reach an equilibrium. Many of these diseases thrive in monocultures or woods with very few species and only a simple structure. Even that favourite, oak with hazel coppice is very vulnerable, because it comprises just two species and management gives little chance of genetic change.
If our woods are to survive the onslaught steps must be taken now to make them more resilient. In practice this means:
• growing a wider variety of species of different ages together – and ideally mixing broadleaves and conifers. Thus if one species is lost that woodland is not lost to the landscape.
• being more adventurous in non-native woodlands in species choice and mix
• recognising that not every tree needs to be a timber tree,
• re-introducing native species such as lime and aspen that have disappeared from many woodlands.
Most importantly a real effort has to be made to reduce deer numbers to a level that will allow woods to recover and regenerate, and to mount a concerted and sustained attack on the scourge of broadleaved woodland - the grey squirrel.
Many of the threats have arrived on our shores as ‘passengers’ on imports – bought in to be sold through nurseries and garden centres or brought back in a suitcase from foreign holidays. The bigger the plant and rootball the greater the chance it could be hiding a new horror. If we are to have a real chance of slowing the spread of new diseases we must all accept stronger import controls and curb our desire for new exotic plants and instant gardens.
Our trees and woods are worth protecting so I for one am up for it.
*For details of the ash monitoring project run by the Adapt Group at UEA www.ashtag.org and for observaTREE www.forestry.gov.uk/fr/observatree