Apple Canker: Causes, Symptoms and Treatment
Apple canker is a fungal disease that affects apple trees and other fruit trees. It is caused by the fungus Neonectria ditissima, which infects the bark and wood of the tree, causing sunken, dark brown or black lesions that can girdle branches or trunks. The disease can reduce the yield and quality of the fruit, and in severe cases, kill the tree.
In this article, we will explain the causes, symptoms and treatment of apple canker, and how to prevent it from spreading in your orchard.
Causes of Apple Canker
The fungus that causes apple canker can survive in infected wood or fallen leaves for several years. It can spread by spores that are carried by wind, rain, insects or pruning tools. The spores can infect wounds or cracks in the bark of the tree, especially during wet weather in autumn and winter.
Some factors that can increase the risk of apple canker infection are:
- Poor drainage or waterlogging of the soil
- Low soil fertility or pH
- High humidity or rainfall
- Frost damage or hail injury
- Improper pruning or grafting
- Stress from pests, diseases or environmental conditions
Symptoms of Apple Canker
The symptoms of apple canker may vary depending on the stage of infection and the type of tree. Generally, the first sign of infection is a small, circular lesion on the bark that is slightly sunken and darker than the surrounding tissue. The lesion may have a red or purple margin and may ooze a sticky liquid. As the infection progresses, the lesion enlarges and becomes deeper, forming a canker that can girdle the branch or trunk. The infected wood may crack or split, exposing the inner tissue. The leaves and fruits on the affected branch may wilt, turn yellow or drop prematurely. The canker may also produce fruiting bodies that release spores in spring or summer.
Some varieties of apple trees are more susceptible to apple canker than others. For example, Cox’s Orange Pippin, Bramley’s Seedling and Golden Delicious are more prone to infection than Gala, Jonagold and Granny Smith.
Treatment of Apple Canker
The treatment of apple canker depends on the severity and extent of infection. The main goal is to remove the infected wood and prevent further spread of the fungus. Some possible treatment options are:
- Pruning: Cut off any branches or twigs that show signs of canker infection, making sure to cut at least 10 cm below the visible lesion. Disinfect your pruning tools between cuts with alcohol or bleach to avoid contaminating healthy wood. Burn or bury the pruned material away from your orchard.
- Painting: Apply a wound paint or sealant to any large cuts or wounds on the bark to prevent fungal invasion. You can also use a fungicide spray or paste to treat existing cankers.
- Fertilizing: Apply a balanced fertilizer to your trees in spring and summer to improve their vigor and resistance to disease. Avoid over-fertilizing or applying nitrogen-rich fertilizers that can stimulate excessive growth and weaken the wood.
- Watering: Water your trees regularly during dry periods to avoid water stress and drought damage. Avoid over-watering or creating waterlogged conditions that can favor fungal growth.
- Mulching: Apply a layer of organic mulch around the base of your trees to conserve soil moisture and suppress weed growth. Avoid piling mulch against the trunk or covering any wounds or cankers.
Prevention of Apple Canker
The best way to prevent apple canker is to maintain healthy and vigorous trees that can resist infection. Some preventive measures are:
- Selecting: Choose varieties of apple trees that are resistant or tolerant to apple canker. You can also use rootstocks that are compatible with your soil type and climate.
- Planting: Plant your trees in well-drained, fertile and slightly acidic soil. Space your trees adequately to allow good air circulation and sunlight penetration.
- Protecting: Protect your