How to prevent coral disease

Which plants are involved?

Coral disease can affect many different trees: maples, horse chestnuts, alders, albizias, hazels, linden trees, magnolias, as well as fruit trees (apple trees, plum trees, cherry trees…) and bushes. It primarily affects plants that are already weakened by disease or injury. However, in an urban medium, it becomes more virulent and can lead to the death of small trees. It spreads rapidly from one plant to another.

How to recognise coral disease?

This disease is easily identified by the appearance of smooth, spherical pustules on the bark, which often measure between 0.5 and 1 cm in diameter. They are initially pink or red, turning brick or black as they mature. In summer, smaller, red, clustered balls may sometimes appear.

When they reach ripeness, the spheres open and release spores that will settle in the cracks of bark or wounds of other plants to infest them in turn.

This fungus generates cankerous lesions, altering the structure of the wood, and causing sudden drying of the shoots. It obstructs the vessels that carry the sap. The buds dry up, the bark deteriorates and splits, entire shoots eventually die.

Coral disease is recognised by the presence of orange or red pustules on the bark (photo Gailhampshire)

How to prevent disease from taking hold?

This fungus primarily develops on dead wood or weakened trees. Keeping plants healthy and maintaining a tidy garden (for example, by removing dead branches) helps to limit risks. In spring, apply fertiliser to your plants and monitor watering while avoiding excess moisture.

When pruning your trees and bushes, make clean cuts with disinfected tools, and cut just after a branching or a bud that acts as a sap sucker. Then, apply a healing paste to the wound to prevent spores from settling. Another technique is to use clay mixed with Bordeaux mixture to cover the wound. Injuries are entry points for many diseases and fungi, so it is important to avoid exposing them to open air until they have healed.

What solutions are available once the disease is declared?

• As soon as you spot coral disease on your trees or bushes, immediately cut off the affected branches using pruning shears, a branch cutter, or a saw.
• If your bushes are entirely affected, fell them to prevent the spread of the fungus to other plants.
• Burn all the parts you have removed.
• Use sealant to aid healing and prevent spores from settling again in the wood.
• Spray a copper-based fungicide, such as Bordeaux mixture.
• Do not plant other species susceptible to this disease nearby or in a location where plants have already been affected.
• Keep a tidy garden and collect dead branches from the ground to burn, as they can harbour spores.