Cankers: Unveiling the Hidden Threat to Plants

Cankers, while often overlooked, are a critical concern in the world of arboriculture, forestry, and gardening. These localized, necrotic lesions on the bark, stems, or branches of trees and shrubs can severely affect plant health and even result in the death of the plant. This comprehensive blog post delves into the complex subject of cankers, exploring their symptoms, causes, types, and detailed strategies for prevention and management.

Understanding Cankers

Cankers are not a disease themselves, but rather a symptom of an underlying infection, typically caused by various fungal or bacterial pathogens. These infections lead to the death of the bark and underlying tissues, creating a noticeable wound or lesion on the plant’s surface.

Symptoms of Cankers

  • Sunken Areas: Cankers often appear as sunken, discolored areas on the bark.
  • Cracking: The bark may crack around the canker.
  • Discoloration: A difference in color compared to healthy bark.
  • Oozing: Some cankers exude sap, resin, or a gum-like substance.
  • Dieback: Infected branches may die back from the tips.
  • Overall Decline: Severe cases may lead to the decline or death of the entire plant.

Types of Cankers

There are several distinct types of cankers, each caused by different organisms and affecting specific hosts.

1. Nectria Canker

Caused by Nectria spp., often affecting hardwoods like maple and birch.

2. Cytospora Canker

Caused by Cytospora spp., known to infect spruces, willows, and poplars.

3. Phytophthora Canker

Caused by water mold Phytophthora, affecting a wide range of hosts.

4. Bacterial Cankers

Such as fire blight in apples and pears, caused by the bacterium Erwinia amylovora.

Causes and Contributing Factors

Understanding the causes and factors contributing to canker formation is vital for prevention:

  • Pathogen Presence: Various fungi and bacteria can infect plants, leading to canker formation.
  • Wounds and Injuries: Pruning wounds, frost cracks, or insect damage can provide entry points.
  • Environmental Stress: Conditions like drought or poor soil quality can weaken plants, making them more susceptible.
  • Poor Cultural Practices: Incorrect pruning, planting, or fertilizing can increase vulnerability.

Prevention and Management

Preventing cankers is generally more effective than trying to cure them once established. However, several strategies can help manage existing infections:


  • Healthy Planting Material: Select disease-free plants and plant in suitable locations.
  • Proper Care: Provide optimal water, nutrients, and mulching.
  • Avoid Injury: Be careful with tools and equipment near plants.
  • Resistant Varieties: Consider planting species or cultivars resistant to known canker pathogens in the area.


  • Pruning: Remove infected branches or stems, cutting below the cankered area.
  • Disinfection: Regularly clean pruning tools with a disinfectant.
  • Fungicides: In some cases, appropriate fungicides may help, following proper guidance.
  • Monitor for Recurrence: Regularly inspect plants for new infections.


Cankers are more than an aesthetic concern; they’re a serious threat to the health and longevity of trees and shrubs. By understanding what cankers are, recognizing their symptoms, knowing their causes, and implementing proper prevention and management strategies, you can protect and preserve your valuable landscape plants.

Whether you’re a homeowner, professional gardener, or land manager, adopting a proactive approach to canker management is essential. Collaboration with local plant health experts, arborists, or agricultural extension services can provide valuable insights specific to your region and plant species. A concerted effort to understand and address cankers contributes not only to the individual plant’s well-being but also to the broader ecological balance and beauty of our natural surroundings.