Defra

Phytophthora ramorum and Phytophthora kernoviae STAKEHOLDERS MEETING Wednesday 6th September 2006.
Ken Haine Building, Duchy College Roswarne Campus, Camborne

QUESTION AND ANSWER SESSIONS

Panel Members

Joan Webber Principal Pathologist (FR)
David Slawson Principal Plant Health and Seeds Inspector (PHSI)
Ben Jones Operations Manager (FC)
Dave Tracy Operation Support Officer (FC)

1. Joan Webber – FR Summary of P. ramorum & P. kernoviae findings and future research

Can you visibly identify the differences in symptoms between Pr and Pk?

It is difficult but possible (around 80% of the time) with an experienced eye.

How does the disease get into trees?

It infects through the bark, which makes the Beech very susceptible as it has a thin bark. Laboratory tests have shown spores lying in water on bark will penetrate and infect given time. The key to whether trees become infected is their proximity to a source of infection, which is usually infected Rhododendrons.

The pathogen, how persistent is it? Six months or more?

That is a reasonable assumption but we are in the early days of the research although we have found that P. kernoviae can persist for at least six months. P. ramorum and P. kernoviae both have resting spore stages and in one study where infected leaf material has been buried, viable P. ramorum has been detected after two years.

Has P. ramorum been found on Beech in the Netherlands?

Yes, and also on red oak (Quercus rubra).

What else causes similar symptoms?

There are a range of Phytophthora spp that will cause similar symptoms of bleeding cankers or lesions on the trunks of trees.

Is there a possibility of animal transfer? We have a number of fallow deer on our land. Is it possible to do research on tissue from culled deer?

This may be possible, but no research has yet been done in this country. There is some anecdotal evidence that infection by P. ramorum followed “runs” used by pheasants on at least one site in this country. Some research has been done in America on the possibility of spores of P. ramorum being carried on the feet of turkeys.

2. David Slawson - DEFRA Pr & Pk EU and National update

Is Scotland included in the survey?

No, Scotland does its own surveys. So far nothing has been found outside nurseries and garden centres.

You talked about destroying the growing medium to achieve eradication. How will this work in woodland?

The measures which I described refer to findings in nurseries and garden centres where destruction of the growing medium is possible. This may not be practicable in woodland although it is advised to destroy as much debris as possible associated with infected plants .

Does this mean you are giving up on woodlands?

Not at all, we will continue to survey and clear sites, as funding is available. Some eradication sites have had negative results when tested. At other sites containment may need to be the primary aim. Overall, whether complete eradication is possible or not, the aim is to reduce inoculum so that trees do not become infected.

Surely clearance work at sites will only cause the disease to spread by releasing spores.

If spores are present the risk of spread exists whether material is removed or not. Destruction by burning on site will minimise the risk of spread. On site where burning is not practical or permission has not been given the low risk method of removal is to cut and then chip this material into skips which are then covered for transportation to a deep burial site. This has been achieved successfully in Cornwall by removal in covered skips for deep burial at United Downs.

In woodland garden sites, the removal of leaf litter will help reduce infection. Root infection may be present (there is conflicting evidence on whether this is significant), but there is no evidence of the pathogens sporulating on roots.

As the cost of clearing is prohibitive would chipping/composting be effective?

The EU Working Group recognised the problem of the high clearance costs, and in their paper have recommended that chipping and composting are given as options. The Dutch have conducted experiments on composting and believe it to be effective if it is managed properly to maintain the required temperatures and durations throughout the compost pile.

Is there EU funding available for clearance work? Would this be an easier way to obtain funds for work?

There are no EU funds available for clearance work. The EU has however provided funds for research. Nationally, there are limited public funds for clearance at the highest risk sites (to be described later in Ben Jones’ talk).

We are using the Woodland Improvement Grant Contract as a mechanism to facilitate the targeting of funds for clearance to the highest priority sites that pose the greatest risk of further spread.

Is living foliage more infective than dead?

Yes, in that living foliage/plants will continue to be infected by the pathogens and therefore carry on being a source of spores. Once plants are killed or removed from the site, there will be some residual inoculum that remains on site in the soil and litter layer, but the amount that remains alive should gradually decline over time.

If complete removal of roots is not possible, is it effective to cut the plants at ground level?

Where complete removal of the plant is not possible, cutting as close to ground level will have to be practiced. Where this has been done, infection of re-growth has been observed possibly because of systemic infection of the entire plant (the Dutch theory) and possibly new re-infection from spores in the litter layer and soil. Chemical treatment of cut stumps to kill re-growth must be carried out.

Has any research been done into woodchip used for mulching? Is there a risk of wood chips, which are used as mulches, or compost spreading infection?

There has been no specific research on woodchip. Imported woodchips are required to be treated which should prevent infection. Although there is no requirement for woodchip moved from site to site, woodchip is considered to be a very low risk. Similarly, compost is considered to pose a very low risk because even if material was infected , the temperature reached during the composting process should be effective at killing Phytophthora spores. The greatest risk comes from movement of infected plants.

3. Dave Tracy – FC Phytophthora Survey 2004 - 2006

Will you be looking for P. kernoviae in England and Scotland?

The Forest Condition Phytophthora Survey will be looking for both diseases in England, Wales and Scotland. The National Re-survey, as recommended by the Interdepartmental Phytophthora Programme Board, will be re-surveying woods last surveyed in 2004, but in England and Wales only.

What about Ireland?

P. ramorum has been found in the Irish Republic on Rhododendrons in woodlands but not P. kernoviae.

If we have only one positive sample over the whole FC survey why are we here?

When P. ramorum was first identified on a tree in Sussex in 2003, the FC, in light of the experience in the USA, instigated a major survey of woodlands in admixture with Rhododendron ponticum in England, Wales and Scotland. Of the c1500 woodlands surveyed in the three countries, there were no positives. In 2005 the Interdepartmental Phytophthora Programme Board recommended that those high and low risk sites in England and Wales which were surveyed in 2004 should be re-surveyed with 20% of the total being surveyed annually. This re-survey commenced in 2005 when 149 woodlands were visited. There were no positives. The 2006 survey has just been completed and we have found only one positive. This is encouraging as it indicates that with the exception of this new positive, the woodlands which were deemed to be at high risk in 2004, are still disease free. The original survey was based on climate, and it showed that in England, Cornwall was a high risk area and this has been borne out by the number of findings of both diseases. While survey work will continue nationwide for the foreseeable future to determine the national picture, the number of outbreaks in Cornwall mean that our (FC and PHSI) survey work will be geared to identify just how widespread the diseases are in the county.

We have a pessimistic picture from PHSI, the FC picture is more positive, why?

The main reason for the apparent difference in results between PHSI and FC is that the FC survey is random whereas PHSI have targeted their surveys with the aim of detecting and eradicating outbreaks e.g. by conducting 3 km surveys around outbreaks in high risk areas. The continuing discovery of new outbreaks in Cornwall does paint a much more pessimistic picture. Our optimism, if we can call it that, is that at this moment in time our national surveys are indicating that the diseases are not nationwide, but largely confined to Cornwall.

4. Ben Jones - FC - Polwhele. Survey and clearance programme in Cornwall

Is there re-infection of plants on cleared sites?

Yes, on sites that have been cleared of R. ponticum there is evidence of re-infection on the re-growth that has occurred on the site. This is being addressed by foliar applications of glyphosate to remove the R. ponticum from site.

Are you able to assess the level of infection in the soil?

Yes we do this by ’Baiting’ for the Phytophthoras. A picture is forming from the results, but we are in the early stages of our research.

Is there a best practice for removal of plants when the sporulation is at its lowest point?

No, a targeted approach is not feasible given the timescales needed for the work.

Should infected trees be removed?

Not necessarily, there is no sporulation from stem lesions. There may be a Health and Safety issue if the tree becomes dangerous. Trees with infected foliage may need to be removed.

Is there any evidence of stem to foliar transmission?

Research continues, different trees have different reactions. For example, the mature bark of beech is susceptible to P. ramorum and P. kernoviae, whereas the leaves are resistant. In contrast, the mature bark of ash is resistant to P. kernoviae but the leaves are susceptible.

How long do the spores last on footwear?

There is a very low risk but it is possible on pathways. P. kernoviae & P. ramorum spores are very resilient so it follows that it will stay on footwear. More general hygiene is needed to control Phytophthoras generally. As a routine we would recommend that tools and footwear should be cleaned at the end of a working day.

5. Ros Smith – Duchy College. Summary of micropropagation project

How do you know that a micropropagated plant does not have P. ramorum or P. kernoviae?

This can be seen in the laboratory when the plants are propagated. It shows up as fungal growth on the nutrient jelly. Before being allowed off site, plants will also be checked over by PHSI and given a licence as pathogen free.

FREE Q & A SESSION FOLLOWING PRESENTATIONS

Propagation from microprop, could this be the way ahead?

Yes, it is one means to produce a disease free plant for restocking, especially where the infected plant is of particular heritage value. However, it will not necessarily save the infected specimen.

Is there any funding for this?

Defra have provided funds to support the micropropagation study at Duchy College. Future funds would need to be considered separately.

Is the whole plant affected or can you prune out areas, what is the policy?

There is still research going on into this matter. PHSI have permitted pruning of high value heritage plants, but experience has shown that pruning is very seldom effective and cannot be relied on as a long-term solution. Pruning can be used to delay the spread so that micropropagation can be carried out but is not an effective measure beyond that. If the disease is not eradicated at a site, there is always a risk that pruned plants may be re-infected.

Surveys – what is being done to look at domestic gardens?

Landscape plantings have been surveyed and when we are contacted by the owner of premises we will survey private gardens. Reassurance that infection is not already widespread in private gardens was provided by a random water-bait study, which did not reveal the presence of P. ramorum in a water course in Birmingham – a large urban area.

Ponticum eradication, what is the future of Rhododendron ponticum in Cornwall?
We need to clearly distinguish between R. ponticum in a woodland environment where it is invasive and will have a detremental impact upon native species and a garden situation where it is potentially desirable. Some funding may potentially be available in the future to address R. ponticum in the wider environment.

Why should I remove Rhododendron ponticum if it is not infected?

As a precaution to manage disease levels on an infected site we strongly recommend the removal of R. ponticum as it is a primary host for both diseases.

What biosecurity products can be used?

Panacide, Enforcer or Mosicide.