Horticulture

Scotland is renowned for the quality of its private and public horticultural collections, and its rich cultural history of plant collecting, allotments and gardening. Horticultural plantings are of significant economic value, as well as providing amenity, health and well-being, cultural and conservation resources. However, pest and pathogens represent a major threat to this highly diverse set of plantings.

Horticultural plantings provide amenity value in public spaces, form structural components of landscaping projects, represent a significant component of urban biodiversity and are central to private, public and heritage gardens. Given the diversity of plants involved in horticulture, there is a corresponding diversity of pests and pathogens of concern, and a particular challenge is the extensive network of plant movement at a range of scales from industrial supply to movement of individual plants between gardens. This results in a highly distributed network of pest and disease vectors. The role of the public is of particular importance for horticulture, in terms of both the ownership of plants in private gardens, and as being a major source of plant movement.

 

 

Projects

Project Lead: Ian Toth
The potato industry in Scotland employs over 2000 people and is worth £250 million to the economy. However, the industry is under serious threat from Potato Cyst Nematode (PCN). PCN comprises two closely related species, Globodera rostochiensis and Globodera pallida, both of which are present in Scotland and, in recent years, the incidence of G. pallida has increased markedly. The use of commercial varieties with resistance to G. rostochiensis have largely halted its spread but there are few varieties with resistance to G. pallida. Statutory testing data collected by SASA shows that the area of land recorded as infested with G. pallida is doubling every 7–8 years and now accounts for nearly 70% of findings. SASA estimates that over 13% of land for growing potatoes is infested with PCN with an estimated increase in spread of 5% per year.

Following a Ministerial round table meeting on PCN in June 2020, the PHC were asked by the OCPHOS to form a working group to identify a clear strategy for dealing with the PCN crisis.
Project Lead: Mariella Marzano
The UK and Scotland have ambitious tree planting targets, with a major driver being carbon sequestration. Scotland’s Forest Strategy outlines a target of 15,000 ha per year. In addition to carbon management, other major drivers for tree planting are commercial forestry, habitat restoration and the establishment of new woodlands for biodiversity and amenity value. Scotland’s Forest Strategy outlines a target of 3,000-5,000 ha of new native woodland per year, and restoration of an additional 10,000 ha of native woodland. This involves planting a large volume of trees. There is considerable uncertainty as to where and how this volume of trees will be sourced, and associated uncertainty as to the biosecurity threats posed. The aim of this project is to improve our understanding of current biosecurity awareness and practices within the arenas of woodland creation/ expansion and habitat restoration in Scotland.

Impact: Determine the main barriers to ensuring that future planting for environmental restoration and conservation will minimise plant health risks.
Project Lead: Mariella Marzano
Large scale infra-structure projects such as transport networks and major housing projects typically include extensive landscaping and planting programmes. These operate at a large scale, often require instant visual impacts (semi-mature shrubs and trees) and face significant cost pressures. The modest scale of domestic production creates challenges in obtaining material from local sources, which can favour low-cost large-scale plant imports with associated risks of pest and disease entry. This project will fill in key knowledge gaps with those responsible for selecting, procuring and planting plants and trees on a large-scale to provide an understanding of how/whether biosecurity features in their decision-making and make recommendations for any changes required to improve bio-secure practices.

Impact: Provide Scottish Government policy with an assessment of the major biosecurity pitfalls and opportunities arising from large-scale landscaping plantings.
Project Lead: Mariella Marzano
Retail horticulture is a large-scale industry in the UK, with ornamental horticulture and landscaping worth an estimated £24.2 billion national GDP in 2017. The industry is characterised by a large volume of individual transactions and the transport of a diverse range of plant materials (with accompanying soil and packaging) to a highly distributed set of final destinations (households). These horticultural sales represent a complex and pervasive vector network, which carries the risk of transportation of pests and pathogens to surrounding parks and gardens, agricultural systems, woodlands, forests and the wider environment. The diversity of the plant material in trade and the multitude of suppliers and recipients creates a major challenge for managing biosecurity. This project will identify decision-makers, their knowledge, attitudes, and behaviours relating to plant health, and assess opportunities and barriers to better plant biosecurity and the potential role of a Plant Health Assurance Scheme.

Impact: This project will enable policy to identify and prioritise plant biosecurity vulnerabilities from non-specialist and online horticultural sales.
Project Lead: Carolyn Riddell
The oomycete Phytophthora ramorum has caused substantial losses of Scottish forests in recent years due to widespread mortality of European larch trees (Larix decidua). Since 2009, legislation and policies have been implemented to control P. ramorum outbreaks on larch including the use of a 250 m larch ‘fire-break’, although it is unclear whether this distance is optimal for disease control. A project funded by Scottish Forestry is using a P. ramorum-specific qPCR assay to compare several spore trapping techniques for quantifying wind- and rain-borne inoculum and to better estimate inoculum dispersal distance. This project adds value to that of the Scottish Forestry-commissioned work, through evaluation of metabarcoding as an alternative method to both monitor P. ramorum inoculum dispersal and detect a broader range of aerially dispersed Phytophthora species. A second objective is to determine the lineage composition of P. ramorum inoculum throughout the observed peak sporulation period.

Impact: Timely management and prioritisation of policy to manage P. ramorum and facilitate early forecasting of other Phytophthora outbreaks.
Project Lead: Katy Hayden
A previous PHC project (PHC2018/11) created an online Resource Bank for plant health threats to the Natural Environment sector in Scotland, which includes an assembly of, or signposting to, available existing resources. The PHC recognised that for the remaining three sectors (Forestry, Agriculture and Horticulture) information on plant health is more available but the quality and relevance to Scotland is often not clear. The aim of this project is to expand PHC’s online resource to signpost users and practitioners to relevant and reliable information and to address a broad spectrum of plant health topics, from diagnostics and control to outreach and education for agriculture, forestry and horticulture sectors.

Impact: Expand the PHC online resource to create a comprehensive and unique signposting resource for plant health information for all sectors.
Project Lead: April Armstrong
The oomycete Phytophthora ramorum has caused substantial losses of Scottish forests in recent years due to widespread mortality of European larch trees (Larix decidua). Infected trees are subject to statutory felling notices in an effort to reduce sporulation potential. Nevertheless, there are concerns about the multiple pathways by which spores might be transferred to new sites. There have been assessments of soil moved by mountain biking and walking/running resulting in evidence to support the Forestry Commission’s Keep-it-Clean campaign. This study will assess soil/plant material collected from commercial harvesting equipment (tyres, treads, mud guards etc.). PHC support will enable a wider range of diagnostic tests to be carried out, testing the robustness of the methods and examining the potential for multiple Phytophthora species to be transferred.

Impact: Add to the evidence base underpinning public and sector-facing biosecurity campaigns and improve disease management and restrict spread of the disease.
Project Lead: Alison Dolan
The brown marmorated stink bug (BMSB) Halyomorpha halys is an invasive species of the shield bug family. It has been intercepted in the UK on several occasions, likely posing a ‘when’ not ‘if’ risk to crops. The BMSB attacks a wide range of hosts including raspberry and sweet cherry, two main soft and stone fruit crops grown in Scotland. The conditions in Scotland appear to be suitable for the establishment of this pest and the Scottish soft fruit industry are concerned about the threat. The soft fruit industry trades with countries with strict biosecurity measures for this pest, and assurances are being sought to verify that every measure is being taken to assess whether the pest is present in Scotland. A failure to do this could have economic consequences for both local markets and on Scottish export markets. This project will survey for BMSB presence and model the potential spread of BMSB in Scotland, including the likely effects of climate change.

Impact: Investigate the suitability of the Scottish climate for establishment and spread of the pest should it be introduced to provide data for a Scottish-specific BMSB risk assessment.
Project Lead: Daniel Chapman
Xylella fastidiosa is a bacterial plant pathogen that can cause disease in a broad range of hosts. Disease symptoms include leaf scorch, wilting of foliage, dieback and plant death. Xylella fastidiosa was first detected in Europe in 2013 in Puglia in Italy and was identified as subspecies pauca which has gone on to devastate olive plantations in this region. There are currently major Xylella outbreaks in Southern France, including Corsica, Italy, mainland Spain and the Balearic Islands. Although Xylella has so far not been detected in Scotland, an outbreak would have serious impacts on any businesses where Xylella is detected and the wider environment. An essential aspect of ensuring that Xylella is not introduced to Scotland is to establish, through modelling, that national surveillance monitoring aimed at detecting a Xylella outbreak is effective. In addition, it is important to identify which epidemiological parameters most strongly influence the effectiveness of surveillance, to guide where future empirical research should be targeted to reduce any uncertainty.

Impact: This project will contribute to Scottish Government’s preparedness measures for the possible arrival of Xylella fastidiosa by ensuring surveillance monitoring is effective and by identifying the key knowledge gaps for effective surveillance.
Project Lead: Andy Evans
The use of pesticides to manage plant pests and diseases is a key management intervention across plant health sectors, particularly in agriculture, horticulture and commercial forestry production. Pesticide withdrawals through legislation, coupled with resistance development, and their impact on plant health have emerged as key concerns for Scottish plant health stakeholders. There is an urgent need to quantify the impact on Scottish plant health that will arise from pesticide withdrawal scenarios and to set this in the context and time frame of alternative management tools. This will be used to inform recommendations on pesticide strategy at the Scottish, UK and EU levels going forward. A synthesis report of available information is required to identify products at risk and work through scenarios for the plant types, pests and diseases of importance in Scotland. This will be a project where cross-sectoral dialogue between the plant health sectors of agriculture / crop production, horticulture, forestry and the environment will be necessary. The project will review existing information and a key output will be summary recommendations appropriate for use by policy makes. The bid must include time to engage with in cross-sectoral dialogue and with Scottish Government staff to discuss and progress early drafts.

Impact: Improved understanding of costs and benefits of pesticide use across Scottish sectors and an impact analysis for the most likely withdrawal scenarios such that key gaps can be identified and their impact quantified in order to inform pesticide policy.

Publications

Horticulture, Agriculture | Final Report and Policy Document

Interdisciplinary Analysis of Plant Health Threats to Arable and Horticultural Crops in Scotland

July 2024

This project took a unique cross-disciplinary approach using biophysical risk modelling combined with social science methods to analyse the threat from emerging plant health threats to both arable and horticultural crops in Scotland.

Horticulture, Agriculture | Final Report and Policy Document

Understanding crop producers’ perceptions around crop health decision making and the impact of that on key metrics such as pesticide usage

July 2024

Increased uptake of Integrated Pest Management (IPM) measures on Scottish farms will be key in improving resilience against pests, weeds, and diseases, and maintaining or improving crop yields and farm profitability, whilst reducing environmental impact and reliance on pesticides. The aim of this project therefore was to improve the flow of IPM knowledge and its uptake and identify the drivers and barriers to further adoption of IPM practices for different decision makers and for different farm types.

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

Biosecurity for plant health: better justification of precautionary measures

May 2024

This project engaged experts and practitioners with knowledge of existing sectoral practices in Scotland, UK and internationally, summarised existing literature and undertook a gap analysis, to generate a better understanding of the rationale for taking precautions and to improve the evidence base with which to justify taking actions.

Forestry, Horticulture, Agriculture | Final Report and Policy Document

Potential of biocontrol for the sustainable management of plant diseases in Scotland: opportunities and barriers

March 2024

Previous PHC projects identified biocontrol as a major element of Integrated Pest Management (IPM) with a role to play in mitigating pesticide withdrawals. However, it is currently unclear how practical biocontrol is as a suitable alternative to pesticides in Scotland, what the opportunities are for deployment across different sectors and what barriers exist to uptake (including regulatory).

Forestry, Horticulture, Environment | Final Report and Policy Document

Action Research to gain a deeper understanding of large-scale biosecurity risks to Scotland

December 2023

This project has developed a systems approach, in the context of plant health biosecurity risks in the retail, infrastructure landscaping and planting in the natural environment, to facilitate further understanding of key organisations and identify general and specific leverage points at which interventions could have a significant effect on the system.

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

A targeted analysis of the impact of insecticide withdrawals in Scotland, in the context of alternative control options

July 2023

Insecticides are commonly used in Scottish agricultural, horticultural, forestry production, and for amenity and natural environment management purposes.  Over the last 10 years, approximately 50% of UK insecticide active substances have been withdrawn due to increasing concern over human health and environmental impacts.  Some of these losses will be mitigated by using alternatives but their practicality and cost under Scottish conditions is unknown.  This project analysed current crop production patterns and insecticide use in combination with how likely different insecticides are to be withdrawn and provided stakeholder views on the impacts of any such losses on their industry, including other control methods that may be adopted.

PHC Annual Report 2022-2023

July 2023

The Plant Health Centre works with Scottish Government, public bodies and stakeholders to provide scientific evidence to help them make important decisions about pests and pathogens that threaten Scotland the most.  Over the past 12 months we have delivered a consistent programme of stakeholder engagement and project commissioning, which are detailed in our annual report. 

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

Biosecurity practices to support plant health: a review of knowledge and practice

March 2023

This research investigated plant biosecurity risks from site visitors, tools & equipment, and large machinery. In addition to reviewing published guidance, UK businesses and organisations were engaged via questionnaires and interviews to explore how these aspects of biosecurity are understood and what procedures may be in place to address them.

Forestry, Horticulture, Environment | Final Report and Policy Document

Identifying the plant health risks associated with plant waste disposal and peat-free growing media and developing best practice guidance for waste disposal and composting across sectors

March 2023

This research focussed on two areas of biosecurity that provide significant risk to plant businesses and the wider environment in Scotland, i) plant waste management, and ii) the constituents of reduced-peat and peat-free growing media.

Enhancing the Plant Health Centre’s communication with stakeholders

February 2023

This project was commissioned to implement a selection of the recommendations made in the PHC stakeholder engagement strategy and communication plan. The team developed strategies to manage time and resources of the Plant Health Centre more efficiently regarding communication of outputs, general information on activities, aims and current issues related to plant health.

Horticulture, Agriculture | Final Report and Policy Document

Perceptions of pest risk and differences in IPM uptake by arable farmers and agronomists in Scotland

November 2022

Pesticide use remains an important tool in managing pest, weed and disease risks to crops and maintaining profitable production. There are several drivers for reducing reliance on pesticides and promoting the uptake of more sustainable practices through integrated pest management (IPM).  By identifying IPM information networks it may be possible to improve the flow of information to farmers by targeting their preferred information sources.  Better informed farmers and agronomists can make better IPM decisions.  Therefore, this project undertook a telephone survey to collect information on currently perceived invertebrate pest and disease threats in Scotland, the level of IPM uptake, and the information sources they relied upon.  

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

Improving knowledge of Xylella fastidiosa vector ecology: modelling vector occurrence and abundance in the wider landscape in Scotland

May 2022

If introduced to the UK, the insect-vectored, bacterial plant pathogen Xylella fastidiosa could be a serious threat to trees and other plants. There is a lack of knowledge about the ecology and distributions of Xylella vectors in Scotland and the potential effects of this on any outbreak of the disease, which this project aimed to address.

Assessment of large-scale biosecurity risks to Scotland

December 2021

PHC commissioned an assessment of large-scale biosecurity risks with a focus on three areas of concern:

  1. non-specialist and online horticulture sales;
  2. landscaping and infrastructure;
  3. planting for environmental benefits.

An additional area was the potential for modelling to support decision making across these areas of concern.  This policy report summaries each report and highlights the key findings and suggested actions.  

Assessment of large-scale plant biosecurity risks to Scotland from non-specialist and online horticultural sales

October 2021

This project focused on an initial exploration of tree and plant biosecurity risks to Scotland arising from large-scale movement of plants via non-specialist (those for which plants are not their primary product type, e.g., supermarkets, DIY and lifestyle stores) and online plant retailers. By better understanding the characteristics of these retailer types, the plant health behaviours they undertake, and the challenges they face, potential avenues were offered for greater engagement and collaboration on biosecurity with this important, but understudied and hard to reach sector.

Assessment of plant biosecurity risks to Scotland from large scale plantings for landscaping and infra-structure projects

October 2021

Planting for large-scale landscaping and infrastructure can typically involve tens of thousands of individual plants, potentially threatening plant health in Scotland due to the biosecurity risks of imports and widespread planting of infested or diseased plants. This project aimed to understand the extent and means to mitigate against such plant biosecurity risks with a focus on mapping the pathways from plant specification through to planting and establishment and highlight different biosecurity awareness for actors, in decision-making and procurement processes.

Assessment of plant biosecurity risks to Scotland from large scale tree plantings for environmental benefits

October 2021

This report features five case studies from across Scotland and examines risks associated with large scale tree planting schemes, levels of awareness around pests and diseases, and how the decisions and actions of those involved can serve to reduce or exacerbate pest and disease related threats and long-term tree health. Each case study was unique in respect to their combination of location, site conditions, ownership, management objectives, species choice, supply chains and management activities. By highlighting best practice and lessons learned, it was hoped to ensure that future planting schemes can be successful and, importantly, reduce the likelihood of pests and diseases being introduced and spread into the wider environment.

The potential of ecological and epidemiological models to inform assessment and mitigation of biosecurity risks arising from large scale planting

October 2021

Large scale planting projects linked to infra-structure such as transport networks and major housing projects or to planting for environmental benefits (e.g., urban greening, woodland restoration) pose high biosecurity risks due to the high number and types of plants involved. This report focusses on whether and how ecological and epidemiological model frameworks can inform assessment and mitigation of biosecurity risks from large scale planting using a combination of literature review and stakeholder engagement.  The project aimed to identify priority steps to develop more useful models and tools for assessing biosecurity risks from planting in the future.

Forestry, Horticulture, Environment | Final Report and Policy Document

Metabarcoding analysis of Phytophthora diversity in spore traps and implications for disease forecasting in the P. ramorum management zone

May 2021

Surveillance and monitoring of airborne pathogens is a key tool in the management of healthy forests and controlling disease outbreaks. A Scottish Forestry-funded project was carried out in autumn 2019 to validate different spore-trapping techniques for monitoring airborne P. ramorum inoculum using a species-specific qPCR assay. This project aimed to add further value to the Scottish Forestry project by investigating the suitability of DNA metabarcoding for screening spore trap samples for P. ramorum and other Phytophthora species, seeking early data for aerially dispersed Phytophthora species that may become problematic in UK forests. The study highlighted the value of both monitoring P. ramorum dispersal and detecting other Phytophthora species, to predict and understand changes in disease severity in UK tree host species. Recommendations included that the use of both rain and wind-borne inoculum capture methods might be advantageous due to the variety of weather conditions under which inoculum can disperse.  Lineage testing in Southwest Scotland should be carried out to look at the prevalence of lineage EU1 in the EU2 area and to monitor for presence of North American lineages. Development of a new DNA barcode more specific to Phytophthora would be beneficial.

Horticulture, Agriculture | Final Report and Policy Document

Monitoring for BMSB in Scotland - Final Report and Policy Summary

March 2021

The increase in global trade brings with it the risk of spread of new pests and diseases into Scotland. Halyomorpha halys, Brown Marmorated Stinkbug (BMSB) is an invasive pest that has already become established in North America and several European countries. The insect aggregates inside houses over winter and can cause problems as an urban nuisance pest in homes as well as being a pest of agriculture. In this project, co-ordinated monitoring for the presence of BMSB was undertaken by teams at SASA and the James Hutton Institute. A reference collection of voucher specimens of common UK stinkbug species was established, including DNA barcoding. A process-oriented climate-based niche model was used by a team at SRUC to determine the areas in Scotland that are suitable for the establishment of BMSB under current and future climates.

Recommendations and suggested 'next steps', including encouraging further surveillance, are detailed in the report and policy summary documents.

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

PHC2020/09: Economic Impact of Pesticide Withdrawals to Scotland, with Case Studies

March 2021

Chemical forms of plant protection are widely used in Scottish agricultural, horticultural and forestry production plus for amenity and natural environment management purposes.  The availability and use of active substances in pesticides are closely regulated and increasing concern over human health and environmental impacts has led to a greater likelihood that some existing approvals will be withdrawn and/or that approvals for new products will not be granted.  Potential impacts from withdrawal of these pesticides are of policy interest and this summary report builds on the data and results from project PHC2018/15 (Potential impacts arising from pesticide withdrawals to Scotland’s plant health) and uses case studies to understand the likely magnitude and distribution of potential impacts and how they may be mitigated. 

PHC2018/15: Potential Impacts Arising from Pesticide Withdrawals to Scotland’s Plant Health

November 2020

The use of pesticides to manage plant pests and diseases is a key management intervention across plant health sectors, particularly in agriculture, horticulture and commercial forestry production. Pesticide withdrawals through legislation, coupled with resistance development and their impact on plant health, have emerged as key concerns for Scottish plant health stakeholders.  This project quantifies the impacts on Scottish plant health that will arise from pesticide withdrawal scenarios and sets this in the context and time frame of alternative management tools. 

Impact of climate change on the spread of pests and diseases in Scotland

June 2020

This project constructed a modelling framework which combined epidemiological and economic modelling.  The modelling framework was used to study predictions of spread and economic impact of pests which are not currently in the UK, including Xylella fastidiosa, Candidatus Liberibacter solanacearum (Zebra chip) and Ips typographus (Eight toothed Spruce Bark Beetle). 

Impact:  A web/desktop application is available to the PHC and Scottish Government to analyse the effects of climate change on the spread and economic impact of new threats. 

Expansion of PHC Online Plant Health Resources

May 2020

This project has expanded the PHC online Resource Bank for plant health threats to the Natural Environment sector in Scotland to include information sources for the remaining three sectors (Forestry, Agriculture and Horticulture). Information sources for Forestry, Agriculture and Horticulture were compiled and evaluated, and a Knowledge Bank relevant to each sector is now online at the PHC website, creating a comprehensive and unique signposting resource for plant health information with relevance to Scotland.

 

Forestry, Horticulture, Agriculture, Environment | Final Report and Policy Document

The use of mobile technology to enhance plant health monitoring and awareness in Scotland

August 2019

The aim of the project was to review existing websites and smartphone apps currently available and applied in the plant health sector and to assemble a detailed overview covering the following points:

  • What options are available in terms of mobile software applications for plant health?
  • What is their primary purpose?
  • Who is the target audience (growers, plant health professionals, citizen science, …)?
  • Which plant health sectors do they cover?
  • Are they reliable and accurate?
  • Is information submitted to a central database? If so, how is this information used?
  • Could they be used globally, or are they limited to certain geographic regions?
Horticulture, Agriculture | Policy Document

Impact on Scottish crops if the molluscicide metaldehyde is withdrawn

December 2018

This report sets out estimates for the crop loss and value to Scottish crop production should the molluscicide metaldehyde be withdrawn. This would leave ferric phosphate as the only available chemical control option. Short term losses are negligible as the substitution of ferric phosphate carries no additional treatment costs and has equivalent efficacy. Longer term there is some risk should resistance arise to this single site mode of action active, and ferric phosphate (although of lower mammalian toxicity to metaldehyde) has some environmental impacts of its own.

Difficult choices to protect gardens and the environment

Authors: Katy Hayden
September 2018

Heritage gardens play an important role in plant conservation. They house collections gathered over decades or even hundreds of years, including varieties of plants that may be overlooked elsewhere, fostering heirloom varieties and preserving biological diversity that is the raw material of adaptation. As well as being beautiful and tranquil sites of cultural heritage, these ex-situ resources are treasure troves of biological diversity. Arduaine Gardens shows us that tough choices can be necessary and important to preserve these collections and the surrounding environment.