The importance of taking personal responsibility cannot be forgotten in the battle against pests and diseases.

IT can be argued that biosecurity is the most important single issue facing the arboricultural and landscape industry today. Of course, there are many challenges facing the industry, but no other single topic arouses so much emotion and has the potential to cause so much damage to our landscape. Biosecurity is the responsibility of all those who grow, specify, order, plant or maintain trees and shrubs.

The DEFRA Risk Register currently lists over 1,000 pests and diseases which have the potential to threaten the UK landscape if they are imported. All readers will hopefully be familiar with ash dieback and the impact it is having on ash trees in both our rural and urban landscapes. The foliage on our chestnut trees turns prematurely brown due to the impact of horse chestnut leaf miner (Cameraria ohridella), while Massaria causes sudden branch drop on London plane and costs enormous sums of money with increased safety inspections necessary in highly used public spaces such as the Royal Parks in London. Oak processionary moth is now spreading throughout London and the Home Counties. It has the potential to become a serious public health issue (some would argue that it already is) and this year reached epidemic proportions in Holland, Germany and other parts of mainland Europe. The pest was imported into the UK on a single oak tree delivered into west London.

Not here yet are Asian longhorn beetle (which could threaten over 30 per cent of London’s tree stock), Emerald ash borer (which, if it arrives, will mop up those ash not wiped out by dieback), plane wilt (a fungal killer of plane trees, currently spreading north through France) or, of course, Xylella (which has the potential to affect not only a wide range of trees but commonly used garden plants such as lavender).

The London i-tree study published in late 2015 provided a detailed snapshot of London’s tree population and assessed it has an asset value of some £6.2 billion. Few can have visited London without being inspired and sometimes awed by the London plane population. Its significance to London cannot be missed. The replacement cost of London plane, should the species be lost, would be over £350 million. Yet hovering in France is a fungal disease called Ceratocystis fimbriata x platani, which is lethal to London plane. Where present, the only recourse is to fell and not replant London plane.

READ MORE: Nurseries and planting strategies: a reciprocal relationship

Individual specimens of Asian longhorn beetle have occasionally been found in the UK, but in March 2012 a breeding population was confirmed by Forest Research scientists in the Paddock Wood area near Maidstone in Kent. More than 4,700 potential host trees were surveyed and 2,166 host trees were removed. A total of 66 infested trees were detected, of which only 24 were found by visual inspection, the remaining 42 only being detected after they were felled. Fortunately, this outbreak was detected before the 2012 adult beetle emergence period, which provided time to inspect and deal with infested trees. The London i-tree report estimates that Asian longhorn beetle could impact on some 3.8 million trees, which represent 31 per cent of the total population. Replacing these trees, were it possible, would cost more than £23 billion.

I have seen the impact of emerald ash borer in the USA and Russia and witnessed the felling of trees affected by plane wilt in both Italy and France.

Forestry Journal: Chart showing increase in pests and diseases (credit: Arboricultural Association).Chart showing increase in pests and diseases (credit: Arboricultural Association).

On occasions such as these, it is easy to point the finger in another direction and ask the inevitable question, “What are they doing about it all?”, never specifying who the ‘they’ is and what they can reasonably be expected to do. The DEFRA team led by Nicola Spence is doing a tremendous amount of good work, but I would suggest that each of us, irrespective of our position in the landscape industry, has a responsibility to ensure that our everyday practices when handling plant material stand scrutiny.

A few years back, at Barcham, we adopted a very strict biosecurity policy which ensured that all imported trees are held on the nursery for at least one full growing season before being released into the landscape, along with other precautionary measures such as independent vitality testing using leaf fluorescence and chlorophyll content, coupled with a rigorous in-house control system forming part of a recent accreditation under ISO 14001.

The Horticultural Trades Association, Barcham Trees and many others have supported the ongoing work of the Plant Health Alliance under the chairmanship of Sir Nicholas Bacon, the immediate past president of the Royal Horticultural Society, which has resulted in the creation of the Plant Healthy Certification Scheme for the industry with an accompanying biosecurity assurance logo for those who are successfully audited. Barcham Trees is pleased to announce that it has successfully completed the extensive independent audit and can now proudly display the scheme’s logo. This is the culmination of a long period of work and support for biosecurity initiatives both in the UK and mainland Europe.

The Plant Healthy Certification Scheme provides a reference point for all those who procure and specify plant material. It provides assurance that nursery companies and others involved in the process of handling plant material have adopted policies and procedures which have biosecurity clearly defined as critical.

The scheme complements and reinforces the work done by many other organisations. The Forestry Commission has done and is doing a great deal of excellent work, which is published on its website. The Arboricultural Association has published a comprehensive guide to biosecurity best practice and the Landscape Institute has published a guide entitled ‘Plant Health and Biosecurity ToolKit’. Both organisations have devoted conference time and space to the issue in recent times.

However, none of the above can replace personal responsibility. It is worth remembering that OPM came into the UK on a single tree, specified by a publicly unknown person and planted by an unknown contractor on behalf of a client. It is likely that one single person was responsible. One tree was imported and planted direct into the landscape without diligent audit processes in place. It is as simple as that. A question I often ask is whether any of you, the readers, would like to be responsible for the importation of one of the pests or diseases mentioned above and the potential decimation of parts of our landscape which might ensue because you or your organisation did not ask the right questions or have the right procedures in place?

The questions are known, and the models are out there, as indicated above, so there really is no excuse. It is up to all of us to respect the work that has been carried out, use the information to amend and examine our everyday practices with regard to biosecurity, use the certification scheme and become one of the growing number of businesses seeking accreditation.

Details of the Barcham Trees Biosecurity Policy and the Plant Healthy Certification Scheme can be found here

Details of the Arboricultural Association’s Biosecurity Guide can be found here

Details of the Landscape Institute Toolkit can be found here

Details of the London i-tree and other similar studies where the implication of pests and diseases have been assessed can be found at here

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