All plants are affected by disease-causing organisms. Damage from diseases is often limited and is a natural part of habitat and host plant ecology. However, increasing global movement of plants and plant products has been accompanied by the effects of introduced pests and pathogens that are not native to Scottish habitats. These organisms find Scottish plant hosts without evolved defences, and can therefore cause major epidemics and ecological damage. Likewise, land use or climate change can increase plant susceptibility and allow native pests to become more damaging. A series of pests that can be considered threats to the Scottish natural environment are listed here.

The list comprises 1) selected long-present or native species that can cause significant damage in plant communities; 2) pests in the UK Pest Risk Register (PRR), already present in the UK, that affect the major genera of woody plants in Scotland; 3) PRA-listed species not yet present but that have been identified as at high risk of arrival and a high impact. In order to identify threat organisms in these habitats, searches can be based on threats to watch out for in a particular habitat, the threats likely to affect a given host, or by the threat itself. Please click through to the information sources for detailed descriptions.

Plant communities occurring in Scotland have been determined using the JNCC National Vegetation Classification (NVC) and the significant native tree and shrub hosts (including long term naturalised trees e.g. Sycamore and Horse chestnut) in these habitats are listed. The habitats have been grouped functionally according to the BAP Broad Habitat types in which those NVC plant communities are most frequently encountered. Note that some hosts and habitats are listed that at present have no known major threats! These are important species and habitats, and information will be added as it becomes known.

1. Determine the general cause and the extent of the disease symptoms. Look for insect damage such as leaf galls or insect exit holes in the bark, or for signs of fungi or other organisms such as leaf spots or brackets on trunks of living trees. Note that some damage can be caused by abiotic factors (such as frost).

2. Use Recommended Sources to try to identify the causal organism and to determine if it is a common and or/native species, and whether it is disease-causing or just a saprophyte (living off a dead plant that something else has killed)*.

3. Search this page by 'Host' for diseases on the Pest Risk Register to find links to detailed information on some of the most important threats and to determine whether you need to notify authorities.

4. Check the Prevention – Biosecurity pages to see how to keep the disease from spreading, and the Control pages for generalised advice for non-notifiable diseases. If you are fairly sure of the pests's identity, check specific resources for targeted recommendations. In the case of notifiable diseases, notify authorities and follow their instructions.

5. Recall that these pages highlight the biggest threats to plants in the Scottish natural environment, but there are many more diseases than listed here! If you do not find a description in these pages that matches the pest you see, you can follow general Prevention – Biosecurity and Control guidance. You can also try to find the exact cause through Self Diagnosis in Recommended Sources.

Most pests encountered will not be notifiable, but if after checking diagnostic and specific resources you think you may have encountered a notifiable pest it is important that you report it quickly. In forest trees in Scotland notify Scottish Forestry via TreeAlert or by email, or if in any other plants notify the Horticulture and Marketing Unit at SASA. Outwith Scotland consult the Plant Health Information Portal for other UK reporting contacts.