How to Accurately Diagnose Tree Disorders

Accurately and efficiently diagnosing tree disorders can be a challenging task because in some cases, issues will appear disguised as something else entirely.


The implications of this go far beyond mere aesthetics; problems with a tree can pose a risk to people, property or structures nearby, particularly if there is something wrong with the roots, such as decay or other environmental factors influencing its stability. 


Although most arborists will be familiar with common types of tree disorders and how these can manifest, there will always be new or mutated problems to contend with, and a swift and accurate diagnosis can ultimately mean the difference between administering effective action or having to fell the tree.


What might be wrong with the tree?


There are many issues which can cause problems for a tree (or any other plant for that matter). Environmental issues such as stress, moisture, extreme temperatures and mineral deficiencies are categorised as non-living factors. Ultimately, of course, the answer in many cases is in selecting an appropriate tree to plant in the first place, ensuring the quality of soil, lighting and other environmental factors are appropriate. However for an established tree suffering from such factors, in some cases, these can be rectified or mitigated to a certain extent.


Living agents can include fungi, bacteria and viruses, insects, mites and other animals. These agents can spread from tree to tree, so if you discover one tree with an infestation, it’s important to have the issue addressed as quickly as possible to prevent spreading and to check other trees in close proximity.


Things to look for


There are several visible indications a tree might have some disorder which can act as an early warning if you know what to look for. Discolouration, visible fungi, powdery mildew on leaves or fluid being released can all give some indication there may be a problem.


A helpful tool in diagnosis are colour plates, matching the discolouration to common disorders. Although this might not guarantee an accurate diagnosis, it can be a good starting point.

Fungal Decay


Although certain types of fungi can form a mutually beneficial relationship with the tree, many tree fungal infections such as brown or white rot can damage it, causing the trunk to become brittle (brown rot) or soggy (white rot).


Unfortunately, it can be difficult to accurately diagnose a fungal disorder until the fungi is showing, which can be too late. The best treatment for a tree suffering from this sort of disorder is by using fungicide sprays or removing the infected area.


On the other hand, once fungi have sprouted, the specific problem becomes easier to identify as each different type of fungus is discernible by its distinct form. Furthermore, many types of fungi will only affect certain trees, so accurately diagnosing a fungal disorder can be simplified once the right questions have been asked.


Bacterial Infection


Trees can also be infected by bacteria or other viruses, causing deterioration in health or soundness, or even death. Again, most bacteria will only penetrate certain trees, so knowing the species and other environmental factors should help narrow down which type of bacterial infection you’re dealing with.


Often, bacterial infections are more common on woody trees or stone fruit trees (such as cherries or peaches) rather than forest or landscape trees. The bacteria or virus enters the tree through wounds caused by animals, insects, or general wear and tear. Keeping a tree free of infection is best done by removing an infected area below the wound and ensuring that any scratches or other possible entry points are minimised.


Things to check


When diagnosing a tree disorder, it’s important to consider all aspects of the tree: not just the obvious symptoms. Develop a systematic approach, starting at the top of and working down the following three steps:


·         Step One: Foliage


Often, one of the first places a tree disorder will manifest is in the leaves or needles of the tree. Check for signs of problems on the leaves such as discolouration, holes or ragged edges, pests visible on the leaves, spots or bumps or leaves which have fallen prematurely. These can all be signs that there is an issue which might be caused by weather damage, injury during transportation or some form of infection or infestation by bacteria, fungi or pests.


·         Step Two: Trunk and Branches


The second step is to check for any damage to the tree’s trunk or branches. Some injuries might be simply explained as an accident when mowing or pruning, but you should also keep an eye out for evidence that the tree has been harmed by an animal or insect. Injury can also be caused by extreme weather such as ice or wind.


You will also need to check for any cracks in the bark and where these are located. Alternatively, are there any wet or sticky substances leaking out? Or evidence of the trunk hollowing or decaying?


Environmental factors may be addressed by either repositioning the tree if it’s small and young enough or by perhaps considering building some form of shelter.


·         Step Three: The “Root” of the Problem


A frequently overlooked aspect of tree diagnosis is very often the most important in establishing an accurate diagnosis: the roots. Many of these problems are man-made and stem from insufficient care being taken during planting or general maintenance.


Some common issues can include the tree being planted too deeply or not deeply enough, disturbance to the soil, for example, to bury a phone line or by landscaping, changes to the soil grade, excessive foot traffic, littering or new plants being introduced to the environment.


Weather conditions may also affect the tree’s roots. Excessive or restrictive groundwater or water supply can cause problems with the root of the tree, as can changes to the temperature or weather.


Modern technology can assist with diagnosing problems with a tree’s roots by utilising non-invasive imagery, akin to the use of an MRI scanner in diagnosing health issues in humans.




It’s easy to take our trees for granted but the truth is that many UK species are under attack from pests and diseases. As well as the essential work of maintaining public safety and property through professional tree management, a key part of any arborist’s work is effective preservation of our treescape, whether in forests and woods, arboretums, public gardens or on private land. 


Diagnosing tree disorders is key to containing the spread of these disorders and so much can be done through better public education. As well as helping the public to spot tree diseases when out and about, it will help publicise the vital conservation role that arborists play for our nation’s trees.