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Five Common Tree Diseases & How To Spot Them

Tree diseases are one of the deadliest things that can happen to a tree. And at an increasing rate, more and more diseases have been inadvertently introduced in the UK from overseas and are now causing issues for our wildlife and vegetation across the country.

Not only are these numbers of diseases increasing, but they’re also causing more problems for tree owners and the public all across the UK. Therefore, it’s important to be aware of the different types of diseases and identify whether your tree is suffering from a disease.

What are the most common tree diseases?

As one of the leading arborists across Buckinghamshire and Hertfordshire, we come across many types of tree diseases on a regular basis. The five most common types of tree diseases we’re seeing are ash dieback, Dutch elm disease, oak wilt, anthracnose and powdery mildew.

Ash Dieback

Ash dieback is one of the most common tree diseases in the UK and is caused by a fungus known as Hymenoscyphus fraxineus. It primarily affects ash trees and is known for its destructive impact on trees across Europe, Asia and the UK.

It spreads through spores produced by fallen leaves and infected twigs and is often helped to spread by things such as rain and wind.

In order to spot ash dieback, you should look out for wilting, blackening and browning of leaves starting from the tips of branches. You should also keep an eye out for diamond-shaped lesions or necrotic spots that appear on the bark. The crown of the tree will also begin to die back and is one of the telltale signs that the tree is infected.

Dutch Elm Disease

Another common tree disease in the UK is Dutch elm disease. This type of tree disease is caused by two closely related fungi known as Ophiostoma ulmi and Ophiostoma novo-ulmi. Dutch elm disease usually affects elm trees and trees within the genus Ulmus.

The disease is spread through elm bark beetles which carry fungal spores from infected trees to healthy ones.

If you think your elm tree may be suffering from Dutch elm disease you should look out for signs of wilting and yellow leaves on individual branches. These patterns typically start at the top of the tree and progress downwards. As the disease begins to progress, the leaves will curl and turn brown. You may also notice dark streaks appearing in the wood beneath the bark, with the tree dying in a few months after you notice these signs.

Oak Wilt

Oak wilt disease is a vascular disease that is caused by the fungus Bretziella fagacearum. It primarily affects oak trees, particularly species in the red oak group (such as northern red oak, black oak, and pin oak), although some white oak species can also be susceptible.

Oak wilt disease is spread through interconnected root grafts between neighbouring trees. It can also move further distances via insects such as beetles, which are attracted to the fungi formed under the bark of infected trees.

In order to spot oak wilt, the symptoms will vary depending on the type of tree species. If it is a red oak tree, the leaves will begin to wilt and brown at the top of the tree and move downward. The leaves will curl and the tree will die in a few weeks or months. If the tree is a white oak, symptoms develop slower with leaf discolouration occurring at the outer margins and progressing inwards.


Anthracnose is a fungal disease caused by various species of fungi. It primarily affects deciduous trees and shrubs, causing foliar damage, twig dieback, and in severe cases, can lead to tree dying. Anthracnose is particularly prevalent in regions with cool, wet weather conditions such as the UK.

The trees affected by this disease include sycamores, oak, maple and dogwood trees with it spreading through rain, wind and infected debris.

In order to spot if your tree has been affected by anthracnose, you will notice the leaves are irregularly shaped and dead in some areas. The leaves may also curl and turn brown, alongside twigs showing dieback.

Powdery Mildew

Powdery mildew is another common fungal disease that trees in the UK can suffer from. It’s caused by various species of fungi belonging mainly to the Erysiphales order. The disease affects a range of different trees and shrubs across the UK and is fairly easy to identify.

It thrives in moderate temperatures and spreads by airborne spores that are easily spread in the wind, by water or by insects.

In order to notice powdery mildew disease, there will be a white or grey powdery substance on the leaves, stems, and buds of infected plants. It starts as small spots and can quickly spread to cover larger areas of foliage. Affected leaves may curl, distort, or turn yellow before premature dropping. In severe cases, it can affect the overall health and growth of the tree.

Resolve Diseased Trees in Amersham and High Wycombe

If you notice a tree on your property is starting to show signs of a particular disease, you should look to have your tree removed as quickly as possible. This is to help prevent the spread of disease further, to other trees on your property and neighbouring areas, helping to reduce the danger of more trees getting diseases.

If you suspect a tree on your property is suffering from disease in Amersham, High Wycombe or anywhere is Buckinghamshire or Hertfordshire; get in contact with Quill Hall Arboriculture today, and we can perform an inspection and help advise you on the next best steps to take.

We also offer a range of services including tree felling, tree pruning, hedge cutting, stump grinding, site clearances and grounds maintenance. For your no-obligation quote for tree trimming or removal, call us on 01494 623191 or enquire online today.