All: I recently attended a forestry event where many sectors of the industry are represented. The Phytopthora ramorum outbreak in Larch is now at very high levels with over 2 million trees lost last year and around 1.6 million scheduled to be felled this year. The information posted below is extensive and I make no apology for that. The full link is here: http://www.forestry.gov.uk/forestry/INFD-8EJKP4 with an exerpt posted below.
The take home message is that anyone in the woods, including stalkers can unwittingly spread the disease. So if you have larch in your woods please be aware of the symptoms and the reccomendations to help prevent it's spread. Members in the South West will be well aware of this by now. However the disease is rapidly spreading so everyone ought to be on the lookout.
Phytophthora ramorum in larch trees - Update
Many readers will be aware of the significance of the recent infection of larch trees by Phytophthora ramorum. In the following article bringing the national situation up to date, we summarise the developments and current situation, and look ahead to the implications for British forestry.
Phytophthora ramorum (P. ramorum) was first discovered in Great Britain in 2002 infecting a viburnum plant propagated in a garden centre in West Sussex. This discovery resulted from surveillance for the pathogen in England and Wales by the Plant Health & Seeds Inspectorate (PHSI), which had begun in 2001 in response to the identified risk posed by this Phytophthora species, which was then unknown in Britain. It has since been found infecting a wide range of plants and trees in all four countries of the United Kingdom and the Isle of Man. Until recently it had mostly affected shrubs such as rhododendron, camellia and viburnum, but only a limited number of trees; and from late 2008 the environmentally important bilberry plant (known as blaeberry in Scotland and winberry in Wales). Globally (Europe and North America), it is known to have more than 150 host species.
It is impossible to ascertain when P. ramorum entered Britain before the 2002 detection, or from whence it came. However, contrary to some views, research has shown that it did not arrive here from the USA, where a different type of the pathogen occurs. The evidence suggests that P. ramorum is native to another part of the world, possibly Asia. Other European countries (Germany and The Netherlands) are now known to have findings of the pathogen (as an unknown Phytophthora) on shrubs dating back to 1993, but these are likely also to have been introduced.
Until 2009, very few trees of any species had been affected in the UK, and in most cases they were growing close to infected “wild” rhododendron, a plant that is abundant in some woodlands and which produces infective P. ramorum spores. Rhododendron ponticum was, and still is, a cause for concern because it is one of the hosts which produce these infective spores, it is invasive, and it is common in woodland. Under the five-year, Defra-funded, Phytophthora Disease Management Programme led by the Food & Environment Research Agency (Fera), which started in April 2009, great efforts have been expended in removing this species and other sporulating hosts from affected woodlands and other affected areas. These efforts particularly target areas known to be at high risk from P. ramorum, building on action taken against P. ramorum since 2002.
In 2009 P. ramorum was found to be infecting and killing large numbers of Japanese larch trees (Larix kaempferi) in south-west England. This was the first time it had been found causing lethal infection (in the form of stem cankers) on a commercially important conifer species anywhere in the world. Only a few ornamental conifers had previously been found affected in Britain, The Netherlands and France before 2009; these were all different types of yew, and were located in nurseries. In addition, a single coastal redwood was also found infected in a garden. Lethal infection has been observed on a non-commercial conifer species, Pacific yew, in the western states of the USA, while non-lethal infection has been observed in other conifer species in the USA, such as Douglas fir, grand fir and coastal redwood. In Britain we have also found Douglas fir to be a host and, unlike the situation in the USA where the impact has been minor, a number of younger Douglas fir trees of about 5 – 10 years of age have been killed in south-west England.
It was then confirmed on a European larch (Larix decidua) in Cornwall, South-west England, in March 2011, and on a small Sitka spruce (Picea sitchensis), another commercially important conifer species widely grown in the British Isles, in the Republic of Ireland. However, the Sitka spruce, a species which had previously been shown in laboratory trials to be moderately susceptible to P. ramorum, was growing under a heavily infected Rhododendron bush and was therefore exposed to heavy inoculum pressure. See "P. ramorum on Sitka spruce" below for further advice.
The major impact on trees in the USA has been focused on broadleaf species. The American strain of P. ramorum has killed millions of North American native oak and tan oak trees, giving rise to the common name of “sudden oak death”. However, that name is a misnomer in Britain. Our two native species of oak, sessile and pedunculate oak (Quercus petraea and Q. robur), have been little affected in the wild, with only a tiny number of cases recorded, and have been demonstrated in laboratory tests to be more resistant than their American cousins. The preferred generic term in the UK for infection by P. ramorum is “Ramorum disease”.
The discovery of P. ramorum-related mortality of Japanese larch in England was followed in 2010 by similar developments in Wales and one small site in western Scotland, as well as in Northern Ireland, The Isle of Man and the Republic of Ireland. Further outbreaks were identified in 2011 in the Peak District of Derbyshire in central England, Lancashire and Cumbria in North West England, and the island of Mull in western Scotland, and Galloway in South-West Scotland. However, so far the number and area of outbreaks identified in 2011 have been significantly lower than those recorded in the previous two years.
P. ramorum is a fungus-like pathogen, one of about 100 in the Phytophthora genus. The word Phytophthora comes from the Greek for “plant destroyer”, and it is arguably the most destructive genus of plant pathogens.
P. ramorum can infect a wide range of trees and other plants, but it does not sporulate (produce reproductive spores) on all the species it infects. One of the reasons why the infection of Japanese larch is of such concern is that it sporulates particularly heavily on Japanese larch needles – much more so than on rhododendron. This means it releases very high levels of inoculum (spores) into the environment, and these are capable of being borne by the wind over considerable distances, especially from tall, mature trees. Apart from infecting Japanese larch needles, it can also infect and kill mature Japanese larch bark, leading to the outward signs of branch dieback and crown death.
Entire trees can be killed by “girdling” as the pathogen invades and destroys the cambium layer, which is the regenerative layer of tissue immediately under the bark. The pathogen appears to be able to kill trees within one growing season after its presence is first detectable, although it might have been present in the tree for some time before that. However, compared with other tree diseases, this is very fast acting.
Phytophthora species in general - and P. ramorum is no exception - thrive in damp environments, which is partly why larch trees only on the milder, moister, western side of Britain have been found affected so far. It spreads easily in moisture and water, so moist air currents, mists, fog and watercourses all provide the potential for movement. It can also be spread as contaminating spores by animals and possibly also by birds, as well as on footwear, vehicle wheels, and machinery and equipment used in forests or other habitats where it is present. This means we cannot afford to be complacent by presuming it will stay confined to larch trees in the west.
It has so far not been confirmed on hybrid larch, but we are closely monitoring and researching this species for any change in this situation.
There is no evidence that it harms Japanese larch’s timber quality, and the pathogen does not appear to be capable of being spread from the timber sawn from infected trees. However, the bark can harbour P. ramorum without producing spores, and it can also transport infected needles and soil as a contaminant trapped in its fissures, and must be destroyed or treated in ways that kill the pathogen.
Maps and other information about all sites found with P. ramorum infection in England and Wales are available on the Fera website at www.fera.defra.gov.uk .
There are two main forms of symptom of P. ramorum infection of Japanese larch:
The foliar symptoms (symptoms on the needles) are not readily detectable during the winter, when larch trees, unlike most other conifers, have shed their needles. However, cankers can be visible all year round, although the resin bleeding becomes less visible once it dries and hardens.
- wilted, withered shoot tips with blackened needles, with the infected shoots shedding their needles prematurely; and
- bleeding cankers exuding resin on the upper trunk and branches.
Diagnosis uses a combination of:
Laboratory tests to confirm the presence of P. ramorum in larch bark and foliage present a number of technical challenges, and return a conclusive result in only about one-third of all symptomatic material sent in for testing, so we cannot rely solely on laboratory tests.
- visual inspection by trained observers;
- field tests of symptomatic bark and needles with test kits known as lateral flow devices (LFDs), which indicate Phytophthora infection to genus level; and
- laboratory tests of bark and foliage samples to isolate the pathogen and confirm its species.
Sometimes other factors can also point to P. ramorum, even when a laboratory test result is inconclusive. Such other factors might, for example, be findings of P. ramorum in larch litter from the forest floor, or infection on Rhododendron ponticum in the under-storey of the forest in adjacent woodland. If the results of these diagnostic methods point to P. ramorum, it will be treated as a confirmed case.
If, however, laboratory analysis confirms the presence of another causal agent, the site will not be classed as infected, but will be kept under surveillance.
No cure has been found, so the objective of any control approach must be to prevent or minimise any further spread of P. ramorum and the damage it causes. The best available scientific advice is to remove and kill the living plant tissue on which the organism depends for reproduction. In the case of infected larch, this means affected trees should be felled or otherwise killed as quickly as possible after detection of the disease and before the next spring or autumn period of sporulation begins on the needles.
The Forestry Commission has suffered extensive infection within its own Japanese larch woodlands, and is undertaking felling on all of its infected sites. We are also serving statutory Plant Health Notices on other woodland owners requiring their infected trees to be felled.
We are ensuring that private-sector interests are addressed and taken into consideration as we develop our strategy for dealing with this threat, through representation on our Outbreak Management Team from the Confederation of Forest Industries (ConFor) and the UK Forest Products Association (UKFPA), and through meetings with key sector representatives. We recognise the burden that this is placing on some forest owners and industry representatives, and want to ensure that, as far as possible, we minimise this.
We have also defined three risk zones in Great Britain, based on the risk of pathogen spread in each from ‘high’ in Risk Zone 1 to ‘low’ in Risk Zone 3. A map showing the risk zones is available in the ‘Advice for Owners and Agents’ section of the information at www.forestry.gov.uk/pramorum. The boundaries of the risk zones are kept under review as the situation develops.
A system has been established for recording the rate of spread of the pathogen based on notifications and aerial survey, and regular updates of the map showing sites can be found at the “Outbreak map” link on our website.
P. ramorum is a quarantine organism listed under EU emergency measures (Commission Decision 2002/757/EC, as amended), and its presence or suspected presence on plants of any sort in Great Britain must be notified to the relevant authority (the Forestry Commission in the case of forest and woodland). National implementing legislation1 gives Forestry Commission plant health inspectors powers to require the remedial actions that, on the best available scientific advice, are deemed to be appropriate and proportionate to the risk posed by the pathogen. This also enables the Forestry Commission to help ensure the Government discharges its obligations under the EU emergency measures to take action to prevent the spread of the disease.
1 The Plant Health (Forestry) (Phytophthora ramorum) (Great Britain) Order 2004 (SI 2004/3213), as amended by SI 2007/3450. The Plant Health (Forestry) Order 2005 (SI 2005/2517), as amended by SI 2006/2696, SI 2008/644, SI 2009/594 and SI 2009/3020
Anyone who suspects the presence of P. ramorum on trees anywhere in Great Britain (England, Scotland and Wales) must immediately notify the Forestry Commission at the following contact points:
or to the Tree Health Diagnostic & Advisory Service by:
- Scotland - email@example.com; tel. 0131 445 2176;
- England - firstname.lastname@example.org; tel. 0117 372 1070;
- Wales - email@example.com; tel. 0300 068 0300;
The contact details for reporting suspected P. ramorum on plants other than trees are:
- e-mail to firstname.lastname@example.org; or
- telephone to 01420 22255.
- ENGLAND & WALES - Anyone suspecting the presence of P. ramorum on plants other than trees in England and Wales should immediately contact their local Fera Plant Health and Seeds Inspector or:
Tel: 01904 465625
- SCOTLAND - Anyone suspecting the presence of P. ramorum on plants other than trees in Scotland must contact the Horticultural & Marketing Unit of the Scottish Government Rural Payments & Inspection Directorate in Edinburgh.
Tel: 0300 244 9972
Statutory Notices that require tree felling or other action for disease management purposes have the force of law, and the Forestry Commission may initiate proceedings against anyone who fails to comply without reasonable excuse. Plant health inspectors may also visit premises where they have reason to suspect that a quarantine organism is present.
- NORTHERN IRELAND - Anyone suspecting the presence of P. ramorum on any plants, including trees, in Northern Ireland must contact the DARDNI helpline:
Tel: 028 9052 4999
Although we have power to do this without permission (except in the case of a private dwelling, where a warrant is required), we will always try to work co-operatively with owners or occupiers. We have published our internal guidance to plant health inspectorson our website so that those whose properties might need to be inspected can find out what to expect.
The vast majority of owners have recognised the necessity of rapid tree felling, and have willingly complied with Plant Health Notices, or have begun taking steps towards compliance. However, any delays in taking action will increase the risk of spread and threaten the livelihoods of other owners and staff of woodlands, nurseries, retail plant outlets and ornamental gardens. We encourage anyone who is experiencing difficulty in complying to contact us to discuss possible ways forward.
Winter felling licence moratorium
It is difficult to detect P. ramorum infection in larch during the winter, when the trees have no needles and the symptoms are much less obvious. Although cankers on the trunks and branches can still be visible, they can be difficult to spot, and result in too many false negatives to be a practicable means of identification.
This means we have to wait until the spring flush of new foliage before we can see whether P. ramorum is infecting any new woodland areas. We want to avoid a situation where we unknowingly permit infected larch to be felled and enter the supply chain, circumventing the biosecurity precautions designed to prevent pathogen spread during timber movements. We are therefore not issuing any new felling licences for larch crops, or crops with a component of larch, until the spring in Risk Zone 1 if their disease status is unknown. Inspections and processing of new felling licence applications for larch will resumed in the spring. With new foliage on the trees in spring, it is easier to distinguish between uninfected stands, which can be felled and marketed in the usual way, and infected stands, to which the biosecurity measures must apply