Common Diseases Affecting Britain’s Trees

The UK government is taking steps to educate people about the threat posed to native trees.

Damage is caused to our trees, woods and forests from insects, pests, bacteria, fungi and other organisms that are often transported from overseas.

Goods that are imported from other countries and people going abroad for a holiday can introduce foreign predators that disrupt the natural eco-system in Britain.

To help prevent, treat and minimise the risk caused by tree pests and diseases, it is important to identify when trees are affected and when to report outbreaks to the local authorities.

According to Woodland Trust, the most common diseases affecting trees in the UK are as follows:

Acute Oak Decline

Acute Oak Decline (AOD) typically affects mature trees that are over 50 years old. Symptoms include vertical, weeping fissures that seep black fluid. If left untreated, the tree will die after four to six year.

The most commonly affected trees are English or pedunculate oak (Quercus robur) or sessile oak (Quercus petrel). Turkey oak, bali oak, holm oak and Pyrenean oak can also be affected.

Ash Dieback (Chalara)

Chalara causes bark lesions on the subtending branch or stem, leaf loss, wilting foliage and a clump of foliage towards the crown. The disease is often fatal as the pathogen destroys new shoots so the branches are unable to grow leaves.

The types of trees that are most commonly affected are European Ash (Fraxinus excelsior), narrow-leafed ash (Fraxinus angustifolia).

Horse Chestnut Canker

According to Forest Research, the number of trees that have contracted Horse Chestnut Canker has risen dramatically since 2000. The cause is predominantly due to a bacterial pathogen, Pseudomonas syringae pv aesculi and, to a lesser extent, Phytophthora.

Trees can be affected at any age and infections are usually terminal. The symptoms are cracks in the bark stem and bleeding on the trunk and branches.

Horse Chestnut Leaf Miner Moth

Horse Chestnut Leaf Miners are small moths with caterpillars that feed off horse chestnut trees. The resulting condition causes leaves to shrivel and develop white, then brown blotches between the veins.

The symptoms become more pronounced as the season deepens. The first signs may not be noticed until June.

If the tree is affected, you should be able to spot caterpillars or circular pupal cocoons when the leaf is held up to the light.

By August, it is possible for almost an entire leaf to be mined. Heavily infested trees will release their leaves earlier in the season.

Although the trees may appear to be dying, they will survive and will continue to produce leaves normally the following year. However, conkers may be smaller.

Massaria Disease of Plane Trees

Massaria disease in Plane trees (Platanus x Hispanic) has become a growing problem over the last decade. It is mostly found in mature trees over 40 years old and, in the cold British climate, causes branches to decay rapidly and die.

Symptoms include strips of dead bark along the top of the branch and dead flaking bark with orange sap wood exposed. Smaller branches die within a year.

London Tree Officers Association has produced a treatment guide that is available for free download.

Oriental Chestnut Gall Wasp

Originating from Asia, the Chestnut Gall Wasp is a pest that harms sweet chestnut trees (Castanea sativa) which are found in Britain. The larvae of the wasp cause abnormal growth (galls) to form on buds, leaves and stalks and trees shed their leaves early.

The first symptom to look out for are green galls that turn red around June. A high concentration of galls weaken the tree and makes it vulnerable to other harmful pests and diseases.

Wasps emerge from the galls later in the summer but does not bite or sting.

Oak Processionary Moth

The processionary moth is a threat to oak trees whilst they are still in their larvae stage. The caterpillars get their name because they march across the bark of trees in a procession and feed off the leaves.

The tiny hairs of the caterpillar contain toxins which the Woodland Trust warn is a threat to the general public as they cause itchy skin, lesions and sore throats.

Sudden Larch Death (Phytophthora ramorum)

Although Phytophthora ramorum is commonly known as Sudden Larch Death, it affects around 150 species of trees and plants including beech, chestnut and ornamental plants including rhododendron, Camellia and Viburnum.

The first symptoms of an infection are the shedding of needles which results in the thinning of the crown. The next stage is for the tree to form an excessive number of cones and the leaves to turn brown, grey and ginger.

Phytophthora Austrocedri

The Phytophthora Austrocedri is an aggressive fungus-like pathogen that attacks juniper and members of the cypress family such as Lawson cypress and Nootka cypress.

Typical symptoms include a spread of red and brown foliage, scattered dieback of shoots or branches and the inner bark will turn from a healthy white colour to orange-brown. In the latter stage, the core will display a diffuse yellow.

Red Band Needle Blight

Red Band Needle Blight is a disease that affects conifers and is caused by the fungus, Dothistroma septosporum. Early symptoms to look out for are yellow or tan spots which later turn red-brown whilst the base remains green.

Needles that become infected will fall off, leading to branches that take on the appearance of a tufted lion’s tail. At the very least, trees will result in a loss of yield and left untreated will eventually cause death.

Sweet Chestnut Blight

The fungus Cryphonectria parasitic is the cause of sweet chestnut blight and is responsible for an epidemic throughout the UK. Symptoms spread rapidly and start by infecting the barks the branches become girdled. The disease does not spread to the roots.

A typical symptom on grafted trees are calluses around the graft. In coppices or orchards, the base of the stem is affected. The blight is identified by orange bodies which have fruits that erupt through lenticels and produce orange spores in moist weather.

In many cases, knowing how to identify the symptoms of tree diseases or insects that are harmful to trees can help prevent death. Contact us for help.

Talk To a Qualified Tree Surgeon

Should you suspect one or more your tree’s is suffering from any of the above diseases it is best practice in the first instance to seek the advice of a qualified Kent Tree Surgeon

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