Forest Research’s Tree Health Diagnostic and Advisory Service (THDAS) received a record number of pest and disease enquiries during the past year (April 2020 to 31 March 2021). As a result of people spending more time in nature, the number of enquiries was about 10% higher than in 2019 and at the highest level since the service was relaunched in 2014.
Tree health enquiries concerned a wide range of species (belonging to 57 genera) and mostly broadleaved tree species. The most common host by far was Quercus (oak; 38% of reports) followed by Fraxinus (ash; 14%) and Castanea (sweet chestnut; 4%).
Ash dieback was the most commonly reported disease in 2020. Almost all of these reports were on ash (on a range of ash species, but most commonly Fraxinus excelsior), but there was one report on the ornamental shrub, Chionanthus virginicus (fringe tree). Ash dieback is a highly destructive fungal disease that is expected to kill at least 95% of the ash in Britain and cause damage estimated at £15 billion. This disease is present in most parts of the United Kingdom, but reports from areas where it has not already been recorded are encouraged to help monitor its spread.
Oak processionary moth (OPM) enquiries made up almost half of all pest enquiries in 2020. OPM caterpillars are pests of oak and a hazard to human and animal health. Native to southern Europe and first detected in the UK in 2005, OPM is subject to a government-led programme of survey and control to minimise its spread and impact. OPM caterpillars can be confused with caterpillars of other species, such as buff-tip moth, gypsy moth and small eggar moth, which explains their presence among the most common enquiries in the table below.
Find out how to tell caterpillars of the different species apart with our online guide.
Chestnut blight was diagnosed in a number of cases in 2020, including two reports from the public through TreeAlert. This is a serious fungal disease of sweet chestnut (Castanea) and infection usually results in the death of the tree. Since 2011 the disease has been found on a restricted number of sites in the UK, principally in central and southern England. The government is taking action to contain and eradicate the disease.
Acute oak decline is a complex disease of oak that has emerged since the 1980s. The disease is caused by a number of agents, especially bacteria, and can kill mature oak trees within five years. Forest Research is leading research to understand the disease and protect oak trees for future generations, for example through the BAC-STOP project.
Most common enquiries
The table below shows a summary of the most common pest and disease enquiries over the past year. However, note that some of these entries are present due to their visual similarity to pests or diseases of concern.
|Top pest enquiries||Top disease enquiries|
|1. Oak processionary moth||1. Ash dieback|
|2. Buff-tip moth||2. Phytophthora diseases|
|3. Gypsy moth||3. Honey fungus|
|4. Oriental chestnut gall wasp||4. Acute oak decline|
|5. Bark beetles (non-regulated Scolytinae)||5. Diaporthe dieback|
|6. Brown-tail and yellow-tail moths (Euproctis species)||6. Sirococcus blight|
|7. Bark beetles (Ips species)||7. Diplodia shoot blight|
|8. Longhorn beetles (Cerambycidae)||8. Plane canker (Neofusicoccum parvum)|
|9. Small eggar moth||9. Dutch elm disease|
|10. Elm zigzag sawfly||10. European mountain ash ringspot-associated virus|
Reporting a tree pest or disease
If you wish to report a tree pest or disease, please use TreeAlert.
Find out more about Forest Research’s Tree Health Diagnostic and Advisory Service.