Have you noticed disfigured, sunken areas on the trunk or one of the branches on your apple tree? It’s most likely an apple canker that you’re up against. Apple canker is a common fungal disease that infects the tree through wounds on the bark made by pruning, animal damage or diseases. A pest called wooly aphid can also damage the bark, leaving it prone to canker. These wounds attract fungal spores to enter the tree and establish a colony.
So you’ve noticed these uncanny, sunken patches on your apple tree? Is there anything you can do about it? Continue reading and you’ll learn all about apple tree canker treatment and preventive measures.
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What Is an Apple Canker?
Apple canker is a fungal disease caused by the fungus Neonectria ditissima. The fungus attacks apple trees, pear, mountain ash, poplar, hawthorn and other woody plants through the bark. The fungus develops sunken, dead areas at the location it attacks, eventually killing off the entire branch. New cankers develop around mid-spring and remain through multiple seasons.
What Are The Symptoms Of Apple Canker?
Oval or round patches of dead, sunken bark is clear evidence that your apple tree is infected by canker. It can quickly kill smaller branches in a single season. On the larger branches, as canker spreads, it creates concentric rings on the bark. Bark can sometimes peel off old cankers, exposing dead wood within.
The branch gradually weakens and ultimately, the entire branch above the canker will die and fall off. Sometimes, the fungus also infects the developing fruits. When this happens, apples will rot and fall off the tree.
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What Damage Does Apple Canker Cause?
Other than the visible symptoms, how does apple canker affect your tree? If you leave it untreated, canker can reduce the tree’s vigor and yield. Eventually, the tree can die under the stress.
If there are more than one fruit trees growing nearby, the fungus can spread to other trees as well, especially between apple and pear trees. To prevent your orchard from damage, it’s important to identify the symptoms as soon as they appear and treat it before the disease takes hold and starts killing off your fruit trees.
Apple Tree Canker Treatment
- Non Chemical Control
The most important part of apple tree canker treatment is pruning to remove the canker. Prune the canker during a dry spell in the dormant season. Since canker is also dormant during this time, pruning disease wood does not risk spreading the disease. Pruning during active growth, on the other hand, presents a potential for the fungal spores to spread to the healthy parts of the tree.
Aim to remove all the infected bark and wood by cutting it out. You’ll need to cut below the area of the infection, until all you see is healthy, clean wood without any sign of infection. Healthy wood will be creamy green in color while the infected portion is brown. Burn all the pruned wood, bark and foliage so that there are no chances of reinfection and sterilize your pruning tools before using them on another plant.
Once the pruning is done, immediately paint the exposed, healthy wood with protective wound paint. This paint, such as Growing Success Prune & Seal, or Medo help prevent the open wounds from being reinfected with canker or other fungal diseases.
- Chemical Control
Besides pruning, there’s some evidence that spraying with a copper-based fungicide, such as Bordeaux Mixture can help prevent the infection from spreading. However, it is not capable of treating an existing canker. By far, pruning diseased portions of the tree remains the only effective approach to treat apple canker.
How To Prevent Apple Canker
There are several measures you can take to protect your apple tree against canker. Here’s what you can do:
- Prevent damage to the bark and branches of the tree. Prune the tree yearly with sterilized tools and coat the exposed wood with protective paint after each pruning.
- Canker is more damaging to the tree growing on heavy, wet soil so improve the drainage of the planting site before planting the tree. If you have clay soil in the garden, amend it with sand and compost to aerate it and prevent waterlogged conditions.
- Apple trees growing in acidic soil are also prone to canker. Test the soil pH to check if it’s within the ideal range, i.e. 5.8 to 7.0. If the pH is lower than the ideal range, raise it by liming.
- Grow varieties that are resistant to apple canker.
Apple Cultivars Resistant To Canker
There are no apple cultivars that can be considered completely resistant to the disease. However, you can find cultivars that offer some degree of resistance, such as the following:
- Annie Elizabeth
- Cockle Pippin
- Lord Derby
- Newton Wonder
- Orleans Reinette
- Merton Russet
- Rosemary Russet
- Crawley Beauty
- Lane’s Prince Albert
Apple Cultivars Prone To Canker
While there are varieties that show some resistance, there are also those that are especially prone to apple cankers. If you don’t want to see apple cankers, or have had trouble with the disease in the past seasons, the following are the cultivars you should avoid growing:
- Lord Suffield
- Worcester Pearmain
- Cox’s Orange Pippin
- Ellison’s Orange
- James Grieve
- Ribston Pippin
Follow the guide above to identify apple canker and employ apple tree canker treatment before the disease progresses and damages your apple tree.