TreeAlert: Enhancing how we monitor tree health

A user reports a poorly-looking tree. From bleeds or exit holes to unusual growths or leaf discolouration, the user takes clear pictures, provides locational details and adds contextual comments about their concerns. They then send it on to the THDAS team at Forest Research as a TreeAlert enquiry.

Initial screening takes place when the enquiry comes in, using the symptoms in the images and described in the comments to allocate the report to the appropriate diagnostic pathology or entomology team member.

Allocating the enquiry also depends on the location: with those that are north of the River Humber being issued to diagnosticians in the Northern Research Station near Edinburgh, Scotland, while enquiries which are south go to the appropriate team member at Alice Holt Lodge in Surrey.

Next, the allocated diagnostician reviews visible symptoms in images and considers any further information provided. If the diagnosis is relatively obvious – with the use of experience and literature resources – a response is emailed to the enquirer with their diagnosis, general facts about the pest or disease and further resources to refer to.

If an enquiry is more complex, ambiguous or potentially a UK priority pest or disease that we are on the lookout for, we will often ask for further images and/or a sample of the organism or affected area in question to be posted to us.

With further images of parts of the tree that may have been missed in the original submission, we can make a more accurate diagnosis. However, if the potential diagnosis is particularly concerning (e.g. a quarantine-level pest), we may contact the enquirer to arrange a field visit as soon as possible.

If a judgement cannot be made from images alone, and with the cooperation with our enquirer, we will obtain a sample through the post. This is the point where processing and diagnostics often differ drastically between the THDAS ‘ento’ and ‘path’ teams.

The sample is taken to the laboratory for examination. Whether this is foliage, bark or wood samples, it is examined with a fine-tooth comb for creatures, evidence of feeding or their excrement. We can skip this step if the sample itself is simply of the insect in question and go straight to an identification.

Pictured above: (left) bark sample being inspected by entomology diagnostician; (right) bark beetles found in the bark and examined under the microscope. Image credit: Forest Research.

Once we have our suspect(s), we go onto our next step of identifying the insect to species level, inspecting its key features (such as the patterns on the wings, shape of the antennae, etc.) under the dissecting microscope. We often use taxonomic keys to help identify the species of invertebrate.

If we are not able to reach a conclusive diagnosis, for example there are no specimens in the sample or the specimens are too degraded, the last resort may be to send the insect or associated larva or excretions for molecular analysis where hopefully the species is identifiable from the DNA sequences. This whole process from start to finish can be completed in approximately one week if all goes smoothly.

Examination of the sample proceeds in the lab, where the processing varies depending on the plant material in question. The four main sample types that path receives are foliage, bark panels, soil, and large fungal fruit bodies. In the case shown below, the foliage sample is initially scrutinized using a stereo microscope. If fungal fruiting bodies are present, they are extracted onto a microscope slide, stained, and their structures are inspected. In some cases, the fungal structures are enough to identify to species level using identification keys. However, some fungi may require different methods of processing to determine species.

Pictured above: Pathology diagnostician inspecting foliage for fungal fruiting bodies. Image credit: Forest Research. 

Samples like bark, lesions on foliage, and some fruiting bodies are treated differently; to get a species level identification, they require culturing. This involves extracting material from where the pathogen is most active, known as the ‘live-dead junction’. The extracted pieces are placed onto a nutrient rich media for the fungi to grow and are checked after three days. If the fungal growth resembles the suspected pathogen, a section of the fungus is chopped out and grown in isolation.

The final stages of processing involve molecular identification, using DNA sequencing to identify the fungal culture to species level. The whole process can take around 2 weeks from when the sample arrives.

Once a diagnosis is reached, the pathologist or entomologist sends a concluding email to the enquirer and the identified pest or disease is added to the TreeAlert database. The email will always hopefully include their diagnosis of the species, background information on its biology and status in the enquirer’s area, as well as helpful resources with further information.

The importance of the data added to the database should not be underestimated, as it allows us to identify any trends in distribution and spread, indicates what the most common tree health problems are, and supports pest and disease management around the UK.