Located within the Alice Holt Forest in Farnham, Surrey, a new £5.8 million state-of-the-art facility is conducting world-leading research into the growing threats posed by tree pests and diseases.

AN invitation to tour Forest Research’s new 370 m2, £5.8 million state-of-the-art Holt Laboratory is an opportunity not to be missed.

After signing in at Alice Holt’s reception, followed by a fire safety briefing, we make our way to the larch-clad Holt Laboratory building.

Dr Ana Perez Sierra, head of Forest Research’s Tree Health Diagnostic and Advisory Service (THDAS) since 2013, welcomes us inside and offers some background on why this new facility was built. “Our teams are growing, volumes of work have increased and we have outgrown the Main Laboratory.”

Forestry Journal: The larch-clad exterior of Forest Research’s new state-of-the-art Holt Laboratory at Alice Holt.The larch-clad exterior of Forest Research’s new state-of-the-art Holt Laboratory at Alice Holt.

The addition of the new Holt Laboratory allows Forest Research to separate its activities into two distinct functions. “The main lab (in the reception building) is now dedicated to work and research on non-regulated pests and pathogens, those that are common in this country, for example honey fungus and powdery mildew. Work in the Holt labs is focused on regulated pests and pathogens.”

Forest Research pathologists and entomologists designed these new ‘contained’ facilities, doubling their research capacity and providing the ability to respond to outbreak situations, providing scientific evidence on recently arrived pests and pathogens, or “working on the knowns (getting ready for what may come from other countries) and also the unknowns (threats emerging as a result of the increased globalisation of trade, travel, and climate change).” 

Phytosanitary security is paramount, ‘contained’ meaning that pests and pathogens are held securely in the facility. “The water used is heat-treated in the lab, the air is filtered throughout the building and all rooms have negative pressure, meaning nothing can escape. Apart from us, anything that comes into the lab has to leave dead. All waste is either killed by submitting them to high or cold temperatures or by incineration.”

Forest Research receives enquiries or samples of material sent via THDAS (from landowners or the public) or those that have been directly collected during specific surveys and outbreaks (or suspected outbreaks) from across England, Scotland and Wales. It also receives samples and suspect material discovered during border interceptions, which can originate from anywhere in the world.

Forestry Journal: A longhorn beetle found (along with larvae) in a piece of oak from Bulgaria.A longhorn beetle found (along with larvae) in a piece of oak from Bulgaria.

All packages sent in must adhere to strict guidelines, three layers of containment being mandatory for all regulated pests or pathogens. Before packages enter the lab, they are placed in an airlock chamber and sanitised (timed sterilisation) and removed only by key-card-carrying authorised personnel.

It is the same for humans. Everyone enters through an airlock chamber, the ‘changing room’, where a bench divides the floor between ‘dirty’ and ‘sanitised’. Essentials, like mobile phones, are sealed in plastic cases and footwear is covered with two pairs of blue cloth overshoes. Nothing that has touched the floor on one side of the bench can touch the other. The airlock’s positive pressure ensures anything unwittingly brought in on clothing does not leave.

From the foyer beyond the airlock, the Entomology Suite (insects and other arthropods) is to the left and the Pathology Suite (diseases) is to the right. In both, the processing of materials and samples follows the same pathway, ‘dirty’ to ‘clean’. “When a sample comes in it is classed as ‘dirty’. The further away it gets from its original form, the more ‘clean’ it becomes.”

We begin in the Entomology Suite. Each lab, bright and white, looks out across clipped lawns and veteran broadleaf trees or through glass partitions to the next room. In the Processing Lab, head of entomology Dr Max Blake offers us white lab coats, saying: “When an import sample comes in (dirty), we don’t know whether it contains a quarantine organism or whether it is a native species. Border interception samples arrive in the lab regularly from our port inspectors and surveillance staff; having facilities in which to open things safely and securely is important to protect our biosecurity.”

From a basic identification, samples move to the Cleaner Lab for further research.

Lengths of Norway spruce bark and timber (approximately four inches in circumference) are laid out on a worktop in the Control Temperature Room. Max holds up a specimen tube containing Ips typographus (8-toothed European spruce bark beetle), the biggest pest to spruce in Europe and of growing concern to the forestry sector in the UK. Small and black (or taupe) with short, spindly legs, these beetles were found this year in Kent, breeding under Norway spruce bark.

READ MORE: What is Phytophthora Pluvialis? Everything we know so far

Max holds up a bark sample riddled with ‘galleries’: deep and lengthy central trenches (grooves running along the grain) bored by adult females, with shallower squiggly grooves radiating out (mostly across the grain) created by Ips larvae feeding activity.

Max says, “We have fought outbreaks in the South East (Kent and East Sussex) for three and a half years now. In 2018, the first incursion (5.5 ha) was detected (and subsequently contained) as part of our routine monitoring on what were, originally, EU Protected Zone surveys. We are virtually unique in Europe in not having this pest as part of our natural fauna. We had to prove its absence to apply trade restrictions on material coming into the UK, which could harbour Ips. Leaving the EU, we continue to have to prove absence of Ips typographus through what is now a ‘Pest Free Area’ for the beetle.”

Last year saw Ips typographus outbreaks across 13 new sites. Using a combination of climate modelling, data collected from breeding galleries at outbreak sites, and (beetle) samples collected from 150 pheromone traps (installed across the South East and beyond, in both FC and private woodlands), Forest Research believes last year’s beetles arrived here in one flight. “Insects have a deterministic life cycle, they grow at a distinctive speed. We worked that back and it matched up perfectly with beetles caught in the traps.

“Where trees are stressed, growing on heavy clay soils waterlogged in winter, or with small root plates that get baked to a crisp in summer, and particularly in trees with tops that have snapped, or trees that have fallen, this is when Ips can get in.”
Outbreaks found on sites last year are currently being eradicated. Each site will be signed off by Max or a senior member of the FC’s Plant Health team. Pheromone trapping continues for a further three years to prove eradication has been effective.

“Over the next 10 years, removing all spruce from the South East will create a ‘Cordon Sanitaire’. A Tree Health Pilot Grant can help with removal costs. It is hoped this grant will be rolled out for more pests and diseases and may bring more woodlands back into active management.”

Using incubators, the Entomology team is modelling ‘what if’ scenarios, such as, “if Ips gets into Sitka spruce, how bad will it be?”

Firstly, to determine the beetle’s life cycle in differing hosts, plastic boxes hosting Plexiglas sandwiches of Ips larvae being reared in Norway and Sitka spruce wood have been placed in two incubators. One incubator simulates summer in south-east England, while the other simulates the Welsh mountains. Larval size and positions are measured daily and breeding successes compared. “Initial results are mixed, but there is a risk to Sitka.”

Forestry Journal: In the Pathology Lab, plastic bags contain samples of western hemlock with yellowing needles.In the Pathology Lab, plastic bags contain samples of western hemlock with yellowing needles.

Secondly, the Cold Store contains plastic crates filled with Ips-infested logs, an experiment where the beetles can choose to breed in either Norway or Sitka spruce logs. Anecdotal evidence suggests that “they seem to prefer Norway, but still breed successfully in Sitka”.

Further research will examine flight patterns and when they swarm. “They can fly at temperatures in the mid-teens. If it is 20 degrees C during the daytime, three days without any rain tends to trigger swarming. That’s near impossible to predict with any certainty, but we are investigating ways of trying to predict this based on weather trends.” 

Are outbreaks of Ips expected in 2022? Max says: “Yes. We are fully prepared for this. We have this laboratory, a robust surveillance programme and new, well-trained staff.”

He is confident populations can be eradicated as they arise.

Back in the foyer, lab coats and one pair of cloth shoe covers are removed and hands are sanitised. Ana leads the way into the Pathology Suite’s Reception Lab, where plant material and soil are processed. Once processed, only clean cultures or selected parts of the material move on, either to the Clean Culture Labs, where they are analysed, or to the Molecular Suite for testing.

In a bright and white lab, plastic bags contain western hemlock and Douglas fir samples that have been sent in from Plant Health Inspector surveys across England, Scotland and Wales. Since January, Forest Research has received 600 similar bags of material, displaying symptoms that could be associated with Phytophthora pluvialis: yellowing needles; dead branches; resinous cankers. Ana says: “When the canker girdles a branch, the part of the branch above the canker dies.”

Samples taken from lesions found under the bark (in the Reception Lab) provide the core material sent to the Molecular Suite (a series of five separate rooms to ensure that no cross-contamination occurs between samples). Using standardised and approved protocols, DNA is then extracted and tested for the pathogen’s presence.

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In the Molecular Suite, preparations for PCR tests (polymerase chain reaction, a test that amplifies or ‘copies’ small fragments of DNA and allows the identification of a specific organism, such as a virus or fungus) are underway. Scientists, the most important resource in this new facility, pipette liquids into sample tubes to be placed in a centrifuge. The test results (displayed onscreen in the PCR Lab), show an exponential curve. These latest samples are Phytophthora pluvialis-positive.

Ana says the first samples of western hemlock received in August 2021 all bore resinous cankers and lesions resembling those caused by Phytophthora. “Investigations identified P. pluvialis, a pathogen that at the time was only present  in radiata pine and Douglas fir in New Zealand, and in Tanoak and Douglas fir in Oregon, USA. There were no published records of this pathogen in western hemlock. In these other locations, it is mainly a foliar pathogen. Here, it affects the bark, causing resinous cankers. This is the first report of this pathogen in Europe. The question is, ‘Where does it come from?’”

Forestry Journal: A bark sample riddled with Ips ‘galleries’: deep and lengthy central trenches (grooves running along the grain), with shallower squiggly grooves radiating (mostly) outwards at right angles across the grain.A bark sample riddled with Ips ‘galleries’: deep and lengthy central trenches (grooves running along the grain), with shallower squiggly grooves radiating (mostly) outwards at right angles across the grain.

Soils tests and surveys of over 1,000 European nurseries made during previous Phytophthora studies revealed no P. pluvialis. “Scientists suggest P. pluvialis could have arrived in New Zealand from the US, probably on machinery wheels.  In the UK, we are not certain where it came from. Apart from western hemlock and Douglas fir, it has not been detected on any other plants and we know of no sporulation hosts.” Ana is currently working with scientists from New Zealand and the USA to investigate the pathogen’s origins in the UK.

In the Clean Cultures room, Ana urges people to report any concerns on TreeAlert. The earlier the report, the sooner Forest Research can act. “You can only act on something if you know about it.” If what is found is new to science, “then you need to prove it and provide the evidence. For example, P. pluvialis was detected on symptomatic western hemlock trees,” not a known host for this pathogen.

Forest Research needed to prove (under controlled conditions) the symptoms observed in the field were actually caused by P. pluvialis. “Once you confirm that, you can reproduce similar symptoms and that you can re-isolate the pathogen, then you can say with certainty that the pathogen is responsible (Koch’s postulate).” Test results were published in February, 2022.

“P. pluvialis is a new pathogen for us and we have yet to see its life cycle here. We first noticed it at the end of summer 2021 and at the time did not see foliar symptoms, only defoliated branches and resinous cankers. We thought we only had cankers. However, during winter we started to see foliar symptoms.”

The next step is to understand how the pathogen behaves: when does the pathogen sporulate? When are the first symptoms observed? How does it infect trees? How does it affect timber? Is it present in leaf litter, in the soil or in streams? “What we have here is probably an aerial pathogen and a canker pathogen.”

Forestry Journal: Dr Ana Perez Sierra, pathologist and head of Forest Research’s Tree Health Diagnostic and Advisory Service, with the head of Entomology, Dr Max Blake.Dr Ana Perez Sierra, pathologist and head of Forest Research’s Tree Health Diagnostic and Advisory Service, with the head of Entomology, Dr Max Blake.

In the Experimental Lab, fitotrons (temperature-controlled, modular, plant growth chambers that can simulate night or day) are being used to test the susceptibility of other tree species to P. pluvialis. Incubators host investigations into the pathogen’s optimum growth temperature. “Scientific evidence and the research done in these labs will be crucial when providing management advice, including whether to attempt eradication or take other steps to contain the pathogen on affected areas.”  

Forest Research collaborates with FERA (Food and Environment Research Agency) and SASA (Science and Advice for Scottish Agriculture) when dealing with outbreak situations, not only supporting diagnostic activities, but providing research evidence to support policy decisions across the nations.

From running P. pluvialis seminars across the UK, Ana will run two more in Europe, helping scientist colleagues (and stakeholders) to know what to look for. “In this job, we look to the horizon to see what is coming (knowns). We have been preparing for pathogens such as Xylella fastidiosa and canker stain of plane, but sometimes we get the unknowns, pathogens on different hosts, or doing something different, in the wrong place.”

In addition to official inspections at ports and airports and active surveillance (aerial, foot and nursery surveys) and readers reporting any concerns via TreeAlert, citizen science projects (Observatree) can contribute to tree health reports on priority pests or diseases that threaten trees. “We are interested in any reports. They help us to understand the health status of trees in Britain.” 

READ MORE: Phytophthora Pluvialis now confirmed in every part of mainland Britain after Welsh find

With Ips typographus on the south-east coast and Phytophthora pluvialis on the west, will there be any forestry resource left? Ana responds: “Yes, because trees are resilient.

Some will die, but not all pests and diseases kill all trees. Things balance eventually. In response to climate change, some trees may adapt over time, some pests might have more than one generation per year, some pathogens will become more active while others won’t, and sometimes one replaces another.”

Forestry Journal: : In the Experimental Lab, fitotrons (temperature-controlled, modular, plant growth chambers that can simulate night or day) are being used to test the susceptibility of other tree species to P. pluvialis.: In the Experimental Lab, fitotrons (temperature-controlled, modular, plant growth chambers that can simulate night or day) are being used to test the susceptibility of other tree species to P. pluvialis.

In the Waste Room, two autoclave machines sterilise all waste. Anything too big for the autoclave is taken away under licence and destroyed by incineration.

Back in the changing room, shoe covers are removed and plastic mobile phone cases disposed of. With the airlock’s positive pressure, anything unwittingly brought out of the lab is sucked back in. We walk back to Alice Holt’s Reception building. In fleeting sunshine, the shadow of a tree falls across the tarmac. The shadow is reminiscent of beetle galleries gouged in bark and serves as a reminder of the urgent work being done here. 

TreeAlert: www.forestresearch.gov.uk/tools-and-resources/fthr/tree-alert/