Rapid Pest Risk Analysis (PRA) for: Peronospora sp. on Aquilegia
This rapid PRA shows that a new species of Peronospora is causing a damaging downy mildew on Aquilegia, but the disease is already widespread in the UK, with limited control options availible.
Risk of entry: Aquilegia downy mildew is only recorded from South Korea and the United Kingdom. There is a relatively small trade in plants and seeds from South Korea. It is possible the disease has a wider distribution than currently reported. If limited to South Korea, new introductions would be very unlikely, but since global distribution is uncertain, entry has been rated as unlikely with low confidence. The confidence in the rating is also impacted by the lack of knowledge on trade volumes or the amount of material that may enter in passenger baggage. It is not known which pathway Aquilegia downy mildew entered the UK on.
Risk of establishment: Aquilegia downy mildew is already widespread in England and Wales and establishment outdoors across the UK in very likely, with high confidence.
Economic, environmental and social impact: No details of impacts have been reported from South Korea. Disease symptoms are severe on Aquilegia and plants may be killed by infection after one or two seasons. It is likely sales of Aquilegia will be negatively impacted by the disease, causing large economic impacts in that sector with high confidence. Loss of garden plants and a reduction in consumer choice will lead to social impacts which are rated as medium with medium confidence. Aquilegia vulgaris is a native species, though also a common garden escapee. Impacts of the disease on wild populations have not yet been reported and it is highly uncertain what impacts may occur. Relatively few species are reliant on Aquilegia as a primary food source, but some of those species that are reliant are considered rare or notable in the UK and could be impacted if there is a large decrease in Aquilegia due to downy mildew disease. Environmental impacts are rated as small, with low confidence.
Endangered area: The endangered area is anywhere where Aquilegia is grown.
Risk management options: Since the disease is established and spreading rapidly, there are limited risk management options. Infested plants should be removed and destroyed, and re-planting of Aquilegia at the same site avoided since spores can survive in the soil for several years. Currently no chemical control options have been identified, and development of resistant varieties is likely to provide the best risk management option.
Key uncertainties and topics that would benefit from further investigation:
Since Aquilegia downy mildew appears to be new to science, and is not formally described, there is an inherent uncertainty throughout the PRA. The following points are key uncertainties:
- Full global distribution of the pest
- How the pest was introduced to the UK
- If, like some other Peronospora species, Aquilegia downy mildew is transmitted by seed
- The potential environmental impacts should the disease spread to wild populations of A. vulgaris, especially on rare invertebrates for which Aquilegia is the primary food source.
- The level of resistance to the disease within Aquilegia species and varieties
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- United Kingdom