Apple Tree Root Rot: Causes, Symptoms, and Treatment
Apple trees are a joy to grow, but they can be susceptible to a disease called Phytophthora root rot, also known as crown rot or collar rot. This disease can affect all species of stone and pome fruit trees, especially when they are between three and eight years old, which are their prime fruit-bearing years.
Symptoms of Apple Tree Root Rot
The symptoms of apple tree root rot appear in the spring and include:
- Delayed bud break
- Discolored leaves
- Twig dieback
- Girdling of the trunk (the bark browns and becomes slimy when wet)
- Water-soaked necrotic tissue at the base of the root that extends up into the graft union
Causes of Apple Tree Root Rot
Apple tree root rot is caused by a fungal disease called Phytophthora cactorum. This fungus thrives in cool, wet conditions and can survive in the soil for many years as spores. The disease is most common during blossom time in April and during dormancy onset in September.
Prevention of Apple Tree Root Rot
The best way to prevent apple tree root rot is to choose rootstocks that are resistant to the disease. Dwarf rootstocks are particularly susceptible, so it is best to avoid them. Some standard-sized apple trees that have good or moderate resistance to Phytophthora root rot include:
- Lodi
- Grimes Golden and Duchess
- Golden Delicious
- Jonathan
- McIntosh
- Rome Beauty
- Red Delicious
- Wealthy
- Winesap
It is also important to select a planting site that is well-drained. Avoid planting trees in low-lying areas or in heavy, poorly draining soil. If possible, plant trees in raised beds or channel water away from the trunk.
Treatment of Apple Tree Root Rot
Once an apple tree is infected with Phytophthora root rot, it is difficult to control. However, there are some measures that can be taken to slow the spread of the disease and save the tree.
- Remove the soil at the base of infected trees to expose the cankered area. Leave this area exposed to air to allow it to dry.
- Spray the lower trunk with a fixed copper fungicide.
- Once the trunk has dried out, refill the area around the trunk with fresh soil late in the autumn.
- Reduce the frequency and length of irrigation, especially if the soil seems to be saturated for long periods of time.
Additional Tips
- Stake or otherwise support young trees to prevent them from rocking back and forth in the wind, which can create an opening around the tree that can collect water and lead to Phytophthora infection.
- Avoid planting the tree with the graft union below the soil line.
- If the tree is already infected, it is important to remove any infected roots and branches.
By following these tips, you can help prevent and control Phytophthora root rot in your apple trees.
