Research undertaken
We employed the CABI Distribution Database for PPDs to analyse 171,481 distribution records of 9472 PPDs across 480 geographical units. We first conducted an ecological assemblage analysis to identify which geographical regions shared the most PPD with Scotland, then applied a machine learning algorithm known as a Self-Organizing Map (SOM) to estimate probabilities of invasion by PPDs currently absent from Scotland and the UK. We then used global climate matching and crop distributions to estimate biophysical risk ratings for absent PPD, focussing on the most important crops for Scotland (barley, wheat, oats, oilseed rape and potato). We used international imports of crop products and live plants into the UK to estimate the risk of arrival by trade, and international tourism data to estimate the risk of PPD arrival through travel. We co-designed with a diverse range of stakeholders (farmers, agronomists, crop breeders, scientists, policy advisors, regulatory bodies, and value chain actors) plausible future scenarios for Scotland’s arable and horticulture sector and considered how risks from PPDs would differ among scenarios. The timeframe for the scenarios was set at 10 years. We elicited stakeholders’ knowledge about potential future pest and disease issues to compare with model results. Finally, we employed the Pest or Pathogen Spread (PoPS) model to investigate how a PPD of particular interest, Colorado Potato Beetle, might invade the UK under a range of different climate scenarios, focussing on the risk of establishment in Scotland following an initial invasion into southern England.

Main findings
There were significant changes in crop cover in 2023 compared with previous years, particularly a large increase in oilseed rape and a decline in oat production. Climate change, as well as socioeconomic factors, are likely to change the composition and distribution of crop production in Scotland which is dominated by barley, wheat, potato, oilseed rape and oats, with soft fruit, grown over a smaller area, also contributing significantly to the Scottish economy. While some recent analyses have considered changing suitability for some individual crops across the UK and there is a predicted decrease in barley yields in Scotland, we are unaware of any comprehensive projections of the suitability of other crops for Scotland under climate change.
Our biophysical risk models identified a number of PPDs of greatest risk to Scotland. PPDs which emerged as being of particular concern included: Wheat thrip (Haplothrips tritici), corn earworm moth (Helicoverpa armigera), wheat common bunt (Tilletia laevis) and CPB (Leptinotarsa decemlineata).
Some of those identified had high unmitigated risk ratings in the Defra Plant Health Risk Register (PHRR), including: CPB, beet root weevil (Asproparthenis punctiventris), the disease vector Hyalesthes obsoletus, pea leafminer (Liriomyza huidobrensis), tarnished plant bug (Lygus lineolaris) and potato virus S.
The potato flea beetle (Epitrix papa) was identified as a risk through travel and has a high PHRR unmitigated risk rating.
Additionally, we consider as a potential threat to Scottish fruit production the blueberry rust pathogen (Pucciniastrum minimum, syn. Thekopsora minima), which was first reported in Scotland in 2021, and as a potential threat to cereal production the wheat stem rust pathogen (Puccinia graminis f.sp. tritici) due to its recent re-emergence in the UK and Ireland.