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Canker Disease

Have you ever noticed large circular wounds or sore-looking areas in your trees? They occur regularly where old pruning wounds or other damage has occurred on the tree. These large wounds are not just unsightly; they can harm or even kill your tree if left untreated.

These types of wounds are known as canker disease. The term "canker" describes a dead area, a blister on a branch, or the trunk of an infected tree. In addition, cankers may appear as circular, discolored areas or depressed places on the bark. You may have noticed some unsightly cankerous-looking wounds in your tree, but what are tree cankers, and why are they on my tree?

Canker diseases are widespread and destructive to many trees and shrubs. A 'canker' is a symptom of an open wound infected by a fungal or bacterial pathogen. Pathogens like fungi and bacteria are common causes of canker-like damage.


There are three main types of cankers:

  1. Annual cankers are caused by fungi not ordinarily able to cause disease unless the tree is under environmental stress and low in health. Infection occurs during the host's dormant season. During the growing season, host callus tissue walls of the canker and prevent further spread.

  2. Perennial cankers are an aesthetic issue but are rarely lethal to the tree. They do, however, weaken its structure and detract from its appearance. In addition, wounds and branch stubs have invaded the fungi during the tree's dormant period.

  3. Diffuse cankers often grow without showing any clear signs. They invade so rapidly that the wood around the fungus will die before apparent symptoms appear. These diffuse cankers often kill the tree.

Unfortunately, because of the way your tree will defend itself against this condition, it can take several years before you notice symptoms from cankers. However, they are still deadly conditions for your trees. Here are the main symptoms to watch out for:

• Wilting

• Dieback

• Stunted growth of new foliage

• Chlorosis (yellowing or discoloration of foliage)

• Early leaf drop (deciduous trees)

• Excessive loss of foliage (evergreen trees)

• Darkened lesions on the bark

• Split bark, sometimes oozing sap or moisture

Starting as a marked dead area, usually round to oval or elongated shape, a canker may enlarge and encircle the twig, branch, or trunk. Canker Disease looks like a legion or cyst on a tree; it often appears as a sappy scab or wound on the bark. Canker Disease will eventually cause the tree's vascular system to become blocked, and nutrients will not flow. The leaves on affected parts are often smaller, pale green or brown, curled, and sparse. When a canker forms on the trunk near the soil line, it is called a crown canker or collar rot.

How did this happen to my tree?

The following conditions will make your trees far more susceptible to cankers.

  • poor watering practices

  • extremely hot or cold weather

  • nutritional imbalances in the soil

  • changes in the surrounding soil

  • In or near new wounds caused by pruning, animals, storm damage, etc

  • Cankers are common in nurseries and plantations where the plants grow together closely. Make sure you inspect new trees closely before planting.

How to help my tree?

If you have noticed your trees showing signs of canker growth, you should contact your arborist immediately. The sooner you can solve the (no pun intended) root problem causing the canker, the sooner you can get the tree back to health.

Here are some things you can do to avoid this issue in your yard:

  • First, when planting, choose disease-resistant varieties and place them in warm, well-drained fertile soil.

  • To avoid overcrowding, consider the size of all your plants when they are fully mature if you are going to plant around them.

  • Remove diseased parts of the plant in dry weather.

  • Overwatering, moist conditions can make it easier for fungal infections to spread. In addition, the soil needs ample time to dry out between watering.

  • Treat bark and wood injuries promptly.

  • Make sure your trees get the required nutrients by fertilizing and feeding them regularly.

Once you remove bacterial canker from your trees, prevention is paramount. Often, trees become seriously infected when they're under stress or lack the proper nutrients. Trees planted in hard soils or where they cannot root deeply are most at risk. Have an arborist inspect the tree, surrounding earth, and plants to ensure the problem will never come back. Because they can be so hard to detect in the early stages, routine checkups with an arborist, at least twice a year, is the best way to prevent diseases like cankers from creeping into your yard.


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