Coral spot

Coral spot is a fungal disease caused by the pathogen Corallomycetella rishbethii (formerly identified as Nectria cinnabarina). This fungus acts primarily as a wound parasite, invading the host plant through damaged bark, pruning cuts, or weakened tissues, where it then develops within the woody structure.

A wide variety of broadleaved trees and shrubs serve as hosts for this pathogen. Common victims include fruit-bearing trees like apple and pear, as well as landscape species such as maple, horse chestnut, and various berry bushes like redcurrant. It rarely attacks perfectly healthy plants, preferring those stressed by drought, poor nutrition, or winter damage.

The disease is easily identified by the appearance of distinctive bright pink or orange-red pustules erupting through the bark of dead or dying branches. These pustules represent the fruiting bodies of the fungus. As the infection progresses, the wood underneath the bark becomes discolored and necrotic, leading to the branch's eventual dieback.

The development of the fungus is heavily influenced by environmental factors such as prolonged wet weather and high humidity, which facilitate spore release and germination. The spores are primarily dispersed by splashing rain and wind, allowing the infection to spread rapidly from diseased wood to fresh pruning wounds or natural bark cracks.

Management and prevention focus on eliminating the source of inoculum. Key practices include:

• Pruning back infected branches to healthy, clean wood;
• Sterilizing all pruning tools between cuts;
• Applying wound sealants to large cuts;
• Improving overall tree vigor through proper fertilization and irrigation.

There is no chemical cure once the fungus has permeated the heartwood of a tree, which makes early detection and rigorous sanitation the most effective ways to manage the disease. Keeping the garden clean of dead wood and maintaining plant health are fundamental steps in preventing the establishment of this pathogen.