For all of us, whether or not we open our gardens to visitors, there are implications for the health of our garden plants and trees from various threats of infection and diseases.
Mike Thornley of Glenarn Garden, Rhu, Helensburgh has attended a recent workshop on these matters.
He sends this report:
PLANT PESTS AND DISEASES WORKSHOP
In 2012 FERA (The Food and Environment Research Agency) organised four plant health workshops in the UK. The last of these was held on 26 November at the Royal Botanic Garden Edinburgh and was attended by representatives from all of the four RBGE gardens, Glasgow and Dundee Botanical Gardens, the National Trust for Scotland, the Scottish Government, SASA, the Forestry Commission, and the Glorious Gardens of Argyll and Bute.
We were reminded that trees and plants were under serious threat, a situation thrown into stark relief by the crisis facing ash trees (from Chalara fraxinea). Government action alone was not sufficient. There was an over-riding need to reduce the risks of contracting diseases and pests, and creating less favourable environments for their establishment. ‘Plant health champions’ were required to ensure that bio-security measures rippled out to horticulture organisations, gardens, and the public. People with this experience will become increasingly important if and when diseases and pests become so widespread that statutory controls, currently in place, are lifted.
Although the emphasis of the day was on Phytophthora ramorum and Phytophthora kernoviae we were reminded of other threats including citrus longhorn beetle, acute oak disease, oak processional moth, chestnut leaf minor moth (now as far north as Newcastle) and chestnut blight, Phytophthora lateralis on Lawson’s Cypress, pine-tree lappet moth, pine needle blight (reported at Glasgow Botanical Garden), as well as ash die back. A point made more than once during the day was that ten years ago these problems were hardly known. The real threats were not only the currently identified problems but also the diseases and pests that may arrive in the next ten years (with a particularly high risk placed on even small amounts of material collected illegally or inadvertently exported from the Far East).
Delegates were invited to give their initial thoughts, and threw out a wide range of interesting points. The changing weather pattern, with periods of near drought followed by high rainfall was putting plants under stress and making them more vulnerable to disease. Eradication of Rhododendron ponticum had been implemented in a number of gardens. Plant passports were not fool proof and the increasing use of the Internet meant that the established nursery trade was being bypassed. The movement of infected plants was the basic cause of our problems. Related to this last point was the view that the movement of plants on a global scale and the homogeneity of crops, was reducing genetic diversity. Looking at this issue at the local level one suggestion was for more reliance to be placed on re-creating woodland slowly by regeneration rather than instantly by planting (a point underlined later when we heard that 50% of all broadleaf trees planted in the UK are imported). The question was asked:
“Can we do anything, or do we have to hobble along?”
Certainly government does believe that it can and has to do something. The mechanism as to how controls on diseases and pests are put in place was explained. These stem from the workings of world trade agreements (to avoid spurious plant health issues being used as justification for trade barriers) coupled with the need for the world to feed itself (and to avoid catastrophic losses of staple foods), via European Union regulations (plant health directives, phytosanitary certificates, and plant passports) to UK and Scottish Government legislation (plant health orders, statutory notices, and controls at points of entry). In addition plant passports and their coding system were explained and the case made for extending the scheme.
Turning to everyday, practical issues bio-security was defined as the measures that can be taken to minimise the risk of contamination and the spread of diseases. A range of actions might be considered including:
• Checking plant passports
• Visit plant suppliers
• Specify clearly and be pro-active in policing contracts; for instance requiring that no fungicides (that can mask phytophthoras) are used
• Avoid large plants, that are difficult to inspect and come with large root balls
• Source small plants or, ideally, grow from seed
• Avoid having delivery vehicles enter the garden
• Quarantine plants
• Wash tools and spray with “Cleankill” or equivalent and clean boots (including scrubbing off mud from cleated soles)
• Ensure that paths have hard and well drained surfaces (not bark)
• Keep the public away from an outbreak site and install notices saying why (a condition if a statutory order has been served)
In terms of horticultural practices the following measures were suggested:
• Avoid susceptible plants; remove host plants such as Rhododendron ponticum.
• Do not plant in water logged pockets
• Reduce density of planting generally, deadwood and open up to allow more light in and air to circulate, create more diversity (and include indigenous plants)
• Prune rhododendrons, particularly where overhanging paths or where branches are near the ground
• Consider carefully where to place labels so that they are visible from paths
• Do not irrigate with a contaminated water supply
• Avoid composting infected leaves (or ensure that the composting temperatures are high - 45 degrees C. for 5 days - and cover to avoid leachate)
A tour of the Royal Botanic Garden Edinburgh provided examples of a number of the measures described above. In addition guidance was given on the use of phytophthora lateral flow devices for testing for diseases. It was also pointed out that greenhouses, especially when heated, create the conditions for the incubation and spread of pests and diseases and bring with them attendant risks such as the consumption of food by the public.
The quarantining of plants was raised on a number of occasions and it became clear that for the amateur, and for many gardens open to the public, this will involve placing plants in a reception area rather than implementing a strict quarantine regime. Plants can then be monitored before they are put out into gardens and any that are showing signs of disease be rejected and destroyed. Ideally plant holding sites should:
• Be sited way from the main collection(s) and garden
• Have only one entry/exit point
• Be covered and have a solid floor
• Have allocated tools (and even clothes) within the area
• Allow only limited access to named persons.
The suggested period for holding plants was 2-6 weeks (depending on the type of plant), which seemed surprisingly short.
The above bio-security measures can be found, in more detail, in FERA’s “Parks and Gardens – Bio-security Best Practice Protocol” which can be down loaded from its website
www.defra.gov.uk/feraThe Health and Safety risk assessment template was seen as being applicable to plants and collections; what is the horticultural activity being undertaken, the nature of the risk, the likelihood and severity of the possible consequences, the appropriate actions and how and when should they be implemented?
A representative from the RHS garden at Wisley explained its bio-security measures and raised a number of issues that are relevant to other gardens. Particular risks included mixture of functions on one site coupled with the concentration of visitors in certain zones. A highly vulnerable area was the entrance and associated pathways. Swopping of plants between gardens, however well intended, creates dangers, as does the bringing onto site of ailing plants for identification (of the plant and/or the disease). Plant purchasing areas should be separate from the garden and arrangements put in place for a plant crèche, to avoid purchases being taken round the garden. Flower shows present particular problems, as do other commercial activities involving floral displays such as weddings. The bringing together, from other sites, of species or cultivars to form collections, for conservation or assessment, creates particularly high risks.
Any organisation and businesses holding important botanical and horticultural collections are likely to develop their own bio-security policies, risk assessments and action plans. Amateur gardeners, however, may feel that these matters are not relevant and that implementing possible measures described above is beyond them. However all those seriously interested in gardens and plants need to force themselves to face these potential problems, and to re-think what they are doing in order that they create safe and sustainable environments for their plants. Much can be achieved by critically examining the potential risks and by implementing those measures that are appropriate to a particular garden’s circumstances.
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As a postscript to the above I heard on the day of the workshop that Phytophthora kernoviae had been identified on Rhododendron ponticum in a hedge on Glenarn Road, not more than 50 m from our garden entrance. This was disappointing given that a week previously the garden itself had been given a clean bill of health, one year on from the statutory notice being lifted on our earlier Phytophthora ramorum outbreak. The inspector had been monitoring the hedge and I am grateful for her persistence and look forward to a notice being served on the owner, further surveys put in place and the outbreak area removed.
However what action could we take in the meantime to minimise the risks to our garden? Glenarn Road is narrow, with no curb, so that vehicles, especially large delivery vans and council cleansing trucks, brush along the side of the hedge, especially when passing. It is not difficult to imagine on a wet day the disease being transferred onto a vehicle and then onto susceptible plants on our drive. For years we have tolerated the overhanging branches in order to preserve the informal look that we work so hard to maintain. However, spurred into action, we have been from bottom to the top of the drive removing all the branches and herbage that overhang the drive. Suddenly there was more light and space and the topography was revealed. We wondered why we had not done this work years ago.
The point is that we cannot afford to drop our guard and that action against diseases can bring wider benefits.
Mike Thornley
FERA = The Food and Environment Research Agency
www.fera.defra.gov.uk DEFRA = Department for Environment, Food and Rural Affairs
www.defra.gov.uk/SASA = Science and Advice for Scottish Agriculture
www.sasa.gov.uk Glorious Gardens of Argyll and Bute
http://www.gardens-of-argyll.co.uk 
