Canker is a term commonly used in the field of tree surgery to refer to a type of plant disease characterized by areas of dead tissue, which grow slowly over time. This disease can significantly affect the health and longevity of trees, making it a critical subject for tree surgeons and arborists. Understanding the nature, causes, symptoms, and treatment of canker is essential for anyone involved in tree care and management.

While the term ‘canker’ might seem straightforward, it encompasses a wide range of specific conditions and symptoms. These conditions can vary greatly depending on the type of tree affected, the specific pathogen involved, and the environmental conditions. This article aims to provide a comprehensive and detailed overview of canker, exploring its many facets and complexities.

Definition of Canker

In the simplest terms, a canker is a localized area of dead tissue on a tree or plant. This dead tissue is often caused by a fungal or bacterial infection, which interferes with the plant’s ability to transport nutrients and water. Over time, the canker can grow, causing further damage to the plant and potentially leading to its death.

However, it’s important to note that not all cankers are caused by pathogens. Some cankers can be the result of physical damage, such as a wound from pruning or a broken branch. These cankers are often referred to as ‘abiotic’ or ‘non-infectious’ cankers, to distinguish them from the infectious cankers caused by pathogens.

Types of Canker

There are many different types of canker, each with its own specific causes and symptoms. Some of the most common types include Nectria canker, Cytospora canker, and Phytophthora canker. These cankers are named after the specific pathogen that causes them, and they can affect a wide range of tree species.

For example, Nectria canker is caused by the fungus Nectria galligena, and it often affects hardwood trees like maple, birch, and beech. Cytospora canker, on the other hand, is caused by the fungus Cytospora chrysosperma, and it’s commonly found on spruce and poplar trees. Phytophthora canker is caused by various species of the Phytophthora fungus, and it can affect a wide range of trees and shrubs.

Causes of Canker

The causes of canker are varied and complex, involving a combination of biological, environmental, and physical factors. At the most basic level, cankers are caused by an injury to the tree’s bark, which allows a pathogen to enter and establish an infection. This injury can be caused by a variety of factors, including pruning, insect damage, or environmental stress.

Once the pathogen has entered the tree, it begins to break down the plant’s tissue, creating a canker. The pathogen continues to grow and reproduce, spreading the infection to other parts of the tree. Over time, the canker can grow large enough to girdle the tree, disrupting its ability to transport nutrients and water, and potentially leading to its death.

Role of Pathogens

Pathogens play a crucial role in the development of cankers. These microorganisms, which include fungi and bacteria, are capable of breaking down plant tissue and causing disease. However, not all pathogens are capable of causing cankers. Only certain species have the ability to infect trees and create the characteristic dead tissue of a canker.

These pathogens are often present in the environment, but they only cause disease when they encounter a susceptible host. This susceptibility can be influenced by a variety of factors, including the tree’s species, age, and overall health, as well as environmental conditions like temperature, humidity, and soil quality.

Symptoms of Canker

The symptoms of canker can vary greatly depending on the type of canker, the specific pathogen involved, and the tree’s response to the infection. However, there are some common symptoms that are often associated with canker. These include areas of dead or discolored bark, often with a sunken or cracked appearance; oozing of sap or resin; and wilting, yellowing, or premature drop of leaves.

It’s important to note that these symptoms can be subtle and difficult to detect in the early stages of the disease. As the canker progresses, the symptoms may become more pronounced, and the tree may show signs of general decline, such as reduced growth, thinning canopy, and increased susceptibility to other diseases and pests.

Diagnosing Canker

Diagnosing canker can be a complex process, requiring a thorough examination of the tree and its environment. The first step in diagnosing canker is to look for the characteristic symptoms, such as areas of dead or discolored bark and oozing of sap or resin. However, these symptoms can also be caused by other diseases or pests, so it’s important to consider other factors as well.

For example, the location and pattern of the symptoms can provide clues about the cause of the disease. Cankers often form on the trunk or branches of the tree, and they often have a sunken or cracked appearance. The presence of fruiting bodies, such as mushrooms or conks, can also indicate a fungal infection. In some cases, laboratory testing may be necessary to confirm the diagnosis and identify the specific pathogen involved.

Treatment of Canker

The treatment of canker depends on the severity of the disease, the type of tree affected, and the specific pathogen involved. In general, the goal of treatment is to improve the tree’s health and vitality, reduce the spread of the disease, and prevent further damage. This can be achieved through a combination of cultural practices, chemical treatments, and in some cases, surgical intervention.

Cultural practices include proper watering, fertilization, and pruning to improve the tree’s health and resistance to disease. Chemical treatments can include the use of fungicides or bactericides to control the pathogen. Surgical intervention can involve the removal of infected branches or the excision of the canker itself. However, these treatments should be carried out with care, as they can cause further damage to the tree if not done properly.

Prevention of Canker

Prevention is often the best strategy for managing canker. This involves maintaining the tree’s health and vitality, avoiding unnecessary injury, and monitoring for signs of disease. Healthy trees are more resistant to disease and are better able to recover from infections. Avoiding unnecessary injury can prevent the entry of pathogens, while regular monitoring can allow for early detection and treatment of the disease.

It’s also important to consider the role of the environment in the development of canker. Factors like temperature, humidity, and soil quality can influence the tree’s susceptibility to disease. By managing these factors, it’s possible to create an environment that is less conducive to the development of canker.


Canker is a complex disease that can have a significant impact on the health and longevity of trees. Understanding the nature, causes, symptoms, and treatment of canker is essential for anyone involved in tree care and management. By taking a proactive approach to prevention and treatment, it’s possible to reduce the impact of this disease and promote the health and vitality of our trees.

While this article provides a comprehensive overview of canker, it’s important to remember that each case is unique, and the best approach to management will depend on the specific circumstances. Always consult with a professional arborist or tree surgeon for advice on managing canker in your specific situation.