Plant Biosecurity - an olive branch?

This is a talk that I had planned to give at RHS Chelsea Flower Show 2022 on the Wednesday at 7am in the Great Pavilion, however I was unable to do so due to catching Covid-19 a few days before. I have published the talk online in case it is of interest to others:

Good morning, I very much appreciate you taking the time out of your busy schedules to listen to my talk about the Plant Healthy initiative this morning.

My name is Alistair Yeomans and I have unwittingly ended up as a plant biosecurity professional. I say unwittingly, as at heart I am a gardener, once professional, but always a keen amateur. It is with an amateur love of plants that I foremost give this talk today, as I know that it is a passion and care for plant life that bonds all who are involved with RHS Chelsea Flower Show.

So I will avoid technical talk about phytosanitary measures or the like. Instead I will simply reflect on some personal experiences that have driven me to work with 20 national organisations to try and stop more of our cherished garden plants and woodland trees succumbing to new and destructive pests and diseases.

You may have noted that I have four pictures, three of them draw upon cultural references to human illness or mortality and the final one - the olive branch - is a symbol of hope. A hope that we, as plantspeople, can do something now to help our plants thrive for generations to come. In short, the references are an attempt at bringing a pinch of pathos to pathology, as I am aware that, in this Aladdin's cave of plants, I will need to employ all rhetorical techniques available to attract attention.

And one final point before I start, all of these pictures are taken with my phone on a recent evening dog walk. In other words they are genuine, not staged or choreographed. They are examples from friends' gardens or community green spaces that l often walk past or through. Taking these photos has made the penny drop even further for me, that the plant pest and disease threat in the UK is not only a scientific area of research or focus of government policy. It is a real problem that is growing in our local landscapes. Moreover, it is starting to cause real upset - emotionally, ecologically and economically.

So, to the first picture - Pandora's box. This is my friend Lilli's garden which is just next to the Oxford university running track, where Sir Roger Bannister broke the four minute mile. About a year ago I received a desperate WhatsApp message from Lilli wondering why her beautiful box plants were dying. Lilli is an artist and has the most wonderful garden. It is a blend of her carefully nurtured plants and sculpture. Her garden is a source of inspiration for her artwork, so for Lilli to notice that her beloved 20 year-old box plants had turned brown in a matter of days was shocking.

With the help of Pippa Greenwood and further WhatsApp messages, we eventually identified that the culprit was the box tree caterpillar. The caterpillar was first detected in the UK in 2008. It is now spreading widely. Along with box blight, this moth has pretty much removed box, the once go-to small evergreen hedging plant, as an option from the garden designer’s botanical palette. It is not just gardens that will be impacted, some of our finest woodwind instruments are made from boxwood, and it is hard to see how the moth or the blight will be controlled in forest situations. These pests will be of cultural significance in other ways, we only have to consider what the possible fate could be of the eponymously named Box Hill in Surrey for an ecological shiver to travel down one's spine.

The moth, originally from east Asia has spread quickly since it's introduction into Europe in 2007. The main way that it spreads is through live plant movement. In other words, growing box plants in nurseries and moving them around the continent for gardening purposes.

Lilli asked, 'Are there other new pests that will harm my garden?' She looked towards her Rambling Rector winding its way through an old apple tree and wondered, 'what about my roses?' I mentioned that there are a number of pests and diseases that we must try to stop the spread of, but seeing how upset she was, I thought then was not the time to point out the existence of the ever lengthening UK Plant Health Risk Register - A database that now contains well over 1200 plant pests and diseases - Pandora's box indeed.

So I asked to take a picture, left and walked along the Thames in the direction of Hogacre community woodland, which brings me onto my next picture - Ash to ashes.

The woodland grows on an old University playing field to the west of the city. I helped plant this mixed broadleaved woodland with about 100 other south Oxford residents in early 2010. The day was celebratory and I was planting next to an academic named Casper, who, on realising that I was a forester, asked me which tree species I thought would grow fastest. Casper and I were planting an area of hazel, and in response I looked towards the ash team nearby and replied, 'I am sorry Casper, our hazels have nothing on the ash.' I imagined that in 10 years or so the ash would be at least double the height of our hazels. Little did I know that on the horizon, and spreading quickly across Europe, was the worryingly named Chalara ash die-back disease.

Unfortunately ash-dieback arrived in Norfolk the next year and its presence was eventually noticed in Oxfordshire around 2015. Nowadays the hazels are around four metres high. Most of the ash trees barely reach two metres before the ash die-back sets in. This fungus renders the trees to exist as a multi-stemmed masses of mainly dead twigs, rather than a single strong stemmed standard, which should easily be reaching beyond eight metres by now. Ash die-back hits young ash trees particularly hard, as the lesions caused by the fungus can easily encircle the relatively thin young shoots. Older ash trees tend to show lesser impacts, but unless robust resistance emerges or is found within the species, it feels like this generation of ash trees will be the last to reach the naturally majestic heights and forms that we associate with our native ash. It is desperately sad to think that ash could be going the same way as our elm trees.

Planting trees is a great joy, and I of course appreciate why society has put such an emphasis on forest creation to fight climate change. However it seems to have passed many people by that 42% of European tree species are now facing a risk of extinction, primarily from invasive organisms such as plant pests and diseases. Many of these injurious organisms have been introduced by humans, mainly through the movement of plants. With tree mortality comes carbon emissions as the wood rots, the exact opposite of what the current rush to plant trees is hoping to achieve. So we must supply our new and existing woodlands with pest and disease free planting stock or run the risk of irreversibly damaging our woodland ecology even further. Our ability to produce timber and biomass fuel may decline too, bearing in mind that wood is one of the most sustainable materials available when produced from well-managed woodlands.

I then walked in the direction of the city centre. On approaching the magnificent Magdalen College rose beds at the front of the Oxford Botanical Gardens, I remembered Lilli's question about what the prospects were for her Rambling Rector. This brings me to my next picture - Ring a ring o' roses.

The splendid array of rose varieties must have focussed my mind, as I recalled that prior to the first Covid-19 lockdown there had been mention of a rose rosette virus in the horticultural press. Thankfully this virus and the microscopic mite that transmits the disease are not in the UK. The virus is causing considerable damage to rose gardens in areas of North America where it is moved unknowingly by the trade. When it eventually appears, it causes witches' broom-like symptoms, where the thorns, leaves and flowers amass into an almost indistinguishable growth on the end of infected stems. It eventually kills the rose plant. If it were to arrive in the UK it would likely spread quickly as the mite is windblown and considerable numbers of ornamental and native roses grow in our green spaces and wider countryside.

Being aware of the rose rosette virus is a good example of a threat where we can work together proactively to help ensure that amateurs or professionals do not bring this virus and the mite into the UK on infected material. For amateurs there is the 'don't risk it' campaign, where travellers are asked not to bring any live plant material, be it novel or sentimental, into the UK in their luggage. For the trade, official systems or checks and corresponding certificates indicate the plants are pest or disease free. However this system is not infallible, as when plants are moved there is often some risk of material being infected.

I then headed for home thankful that rose rosette virus was not in the UK. On nearing my house I approached one of my favourite private gardens. It is a small southwest facing front garden with an olive tree underplanted with a bed of lavender. It is not a novel planting scheme, however it reminds me of my time when I ran a small nursery in the Alentejo region of Portugal. Although simply beautiful, I have, with another disease in mind, been monitoring this coupling of species for a few years now.

This brings me onto my final slide - olive branch - which is really the focus of my talk. We are now increasingly aware that around the world there are damaging pests and diseases spreading into new areas. In some cases this is causing concern for food security. For these reasons, 2020 was designated the United Nations International Year of Plant Health, although it was unfortunately overshadowed by a major human health issue. In recent years one such disease that has caused great concern in the horticultural trade is a bacterial disease called Xylella fastidiosa.

In the UK olive trees have arguably become the poster child for this bacterial disease. This is unsurprising, as it is images of desiccated ancient olive trees being destroyed in Southern Italy and the havoc wreaked on the farming communities that are evoked when Xylella is mentioned. However, it can infect over 650 other plant species, many of which we use as garden plants here in the UK, such as rosemary, periwinkle and lavender. It also infects native forest species such as oak, maple and cherry to name but a handful. This disease is not in the UK but there are insect vectors here that could spread the diseases if it did arrive. As Xylem feeders, our harmless native spittle bug could become a potential vector which can be seen on the lavender in the picture. The word vector is used in the sense that the bug can potentially transmit the virus in its saliva, and once in the plant, the bacterium multiplies and blocks the plants water supply channels causing it to wilt. Due to the broad host range of this disease, the European Commission describes “Xylella as one of the most dangerous plant bacteria worldwide, with huge economic impact for agriculture, public gardens and the environment”.

The advice is often to choose alternative plants with similar attributes when a pest becomes established in a species, although this approach will be of limited use for pests and diseases with broad host ranges. Substituting Ilex crenata for box is a good example of this practice. Although seemingly a fix, I suggest this is short-term thinking. As a note of caution, I recall a sentiment from the late Dr Peter Savill who was the Reader in Forestry at Oxford University. During a Royal Forestry Society tour of an Oxfordshire woodland in 2012, Peter reflected on the recent upsurge of new tree pests and diseases and expressed concern that one day we may run out of tree species to plant that will grow with good health.

You may have noted that there is a question mark at the end of each picture title. This indicates that we still have a great deal to learn. The question mark is also relevant as now that we know there is a problem - we must ask what can we do to help protect our plants?

This is where the Plant Healthy Certification Scheme aims to help. Established partly due to a plant health summit at Highgrove in 2018, this scheme aims to empower professionals who handle plants to take a greater responsibility for the plants they source and grow. The initiative compliments official inspections by minimising the risk of spreading plant pests further. This is done by carefully assessing the pathways for pest and disease entry, the species sourced, their origin and the range of pest and disease species that could be problematic. It also requires that the businesses and organisations that grow, handle or manage plants establish other plant biosecurity measures such as staff training programmes, monitoring regimes and sterilisation procedures. These are all with a view to avoid introducing plant pests and diseases, but in the event they do occur, to spot them quickly, report them to the authorities with a view to controlling them quickly before they get a foothold.

So, the scheme's focus is on intelligence, pro-action and shared responsibility. Cooperation throughout commercial supply chains and between professionals will be essential as, it is only by working together, that we can be Plant Healthy.

Thank you for your time.