In October 2024, Matt and I received an invitation to Blickling Estate for Acute Oak Decline (AOD) training led by The Forestry Commission. We were absolutely thrilled at the opportunity to meet with specialist Nathan Brown and further our knowledge and understanding of this devastating disease.
During this training event, we were taught the leading theories as to what may be causing this decline in our oak trees and what common factors have appeared over the many years of research Nathan and his colleagues have carried out.
What is Acute Oak Decline?
Acute Oak Decline can be identified through a variety of symptoms, but it should be noted that not all of these symptoms may be present on trees with AOD. Similarly, not all trees with these symptoms are suffering from AOD. Symptoms that you may see include:
- Dark weeping lesions on the main stem
- Crown dieback
- D-shaped exit holes on the outer bark layer caused by the agrilus beetle.
- Vertical or horizontal cracks on/within the main stem
- Callus tissue
For more details, please take a look at our blog post which takes a more in-depth look at AOK.
Damage caused by the agrilus beetle
1 out of 3 affected trees can be seen with exit holes caused by the agrilus beetle, commonly known as the two-spotted oak buprestid or “oak jewel beetle”. These small insects are native to the UK and Europe, and whilst there is no definite confirmation that this particular beetle causes AOD, there is a wider concern that it does have a role to play in the overall decline of oak trees. This is due to its frequent recorded presence in areas affected by AOD.
Damage caused by other factors
Other common factors seen in trees affected by AOD include up to three kinds of bacteria: Brenneria goodwinii, Gibbsiella quercinecans, and Rahnella victoriana. Environmental factors such as low levels of rainfall, high temperatures, and high deposition of nitrogen oxides are also recorded in areas where AOD is prevalent.
Although it may seem daunting to consider the fate of our native oaks against AOD, research has shown that around 40% of monitored trees have produced callus tissues over their decaying sections and seem to enter a state of remission against the disease.
Is there a cure for acute oak decline?
Although there is currently no way to cure AOD, there have been many discussions on how to mitigate the spread. We urge our readers to be considerate of biosecurity when travelling from site to site, woodlands to nature reserves, to monitor trees within their local area or their own gardens and make reports on TreeAlert when necessary.
Learning to identify common tree diseases
Over the last century or so, we have seen several of our native trees affected by complex diseases caused by a manner of elements. Most commonly known is Dutch Elm disease, which has all but decimated trees in the Ulmus genus across multiple continents, though some resistant species or variants remain.
Learning how to identify these diseases helps us as arboriculturists understand the reactive way that trees combat disease and what we can do to slow the spread or whether there is potential to eliminate these factors entirely.
Our readers can take part in this research by learning how to identify AOD and report potential cases on applications such as TreeAlert, a service set up by Forest Research to track all kinds of diseases, pests, and pathogens affecting all species of trees. Further information about TreeAlert can be found on the Forest Research website.
Advice for tree health and diseases
If you’re concerned about the health of your trees or want expert advice on tree care, consult Dr. Stump today. We can provide arboricultural expertise for the mitigation of stubborn tree diseases such as Acute Oak Decline.
