Find out how to recognize canker and what curative and preventive treatments to apply to fight this disease.
What is canker?
Canker is manifested by necrosis of the bark on the trunk or branches, of bacterialor fungal origin. Highly contagious, it mainly affects fruit trees, conifers and roses.
Cankers caused by fungi
Fungi, such as Coryneum cardinale or Neonectria ditissima, cause fungal cankers. Their spores, carried by the wind, find refuge where the bark is vulnerable (wounds, cracks, etc.). A diseased tree can easily contaminate its neighbours.
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Cankers caused by bacteria
Bacterial cankers mainly affect fruit trees, especially cherry, apple, plum, peach and apricot trees. They are caused by bacteria of the genus Pseudomonas. They appear mostly in autumn, when trees go dormant.
How to identify canker?
You can recognize canker by the appearance of brown, concave spots on the trunk or branches, which spread quickly. They are often accompanied by cracks and deformities in the bark. In the case of bacterial canker, golden gum discharge and small holes in the leaves can be seen on your fruit trees.
You can recognize canker by the appearance of brown, concave spots on the trunk or branches, often accompanied by cracks and deformities in the bark. Copyright (c) 2020 SrideeStudio/Shutterstock. No use without permission.
Which trees are affected by canker?
Canker can affect all fruit trees, mainly cherry and apple. As for ornamental plants, the rose bush is particularly susceptible. Other trees and plants such as oak, ash, plane tree, poplar, vine and rapeseed are also vulnerable to this disease.
How to treat canker?
Treatment for canker requires an adapted approach, depending on the severity of the infection.
- If you observe a minor infestation, you may want to consider treating the entire tree, including the foliage, with Bordeaux mixture, preferably in late summer or early fall. Be careful when it comes to dosing, however, because in high doses, copper can be toxic to ecosystems.
- If the disease has largely invaded the tree, it may be preferable to cut it down entirely to prevent the canker from spreading to neighbouring trees.
- If a single branch is affected, you can try to remove the canker by carefully removing all infected parts. Scrape the bark and wood well until you reach the healthy parts, then apply a fungicide and healing putty to the wound, before treating the entire tree withBordeaux mixture.
When it comes to bacterial canker, copper can be used, although its effectiveness is limited. A bacterium-based biological specialty, Bacillus subtilis, is available to combat this type of canker. You can easily find them in garden centres and specialist shops.
How to prevent canker?
Here are some good things to do to prevent canker:
- Clean your pruning tools after each use and disinfect them with alcohol;
- Respect pruning periods and avoid rainy periods;
- Avoid planting species susceptible to bacterial canker in clay, poorly drained, moist soils;
- At the end of winter, brush the bark with the following mixture: 3 parts kaolin clay, with fungicidal and bactericidal properties, for one volume of fresh cow dung. Add a little black soap and water to bind it together. This natural canker treatment is said to be effective in prevention, but should not exempt you from regularly inspecting your trees, to react quickly as soon as the first symptoms appear.