Bark necrosis of fruit trees

The causative agent of this disease is the ascomycete fungus Rugonectria rugulosa. This pathogen is known for its ability to infect the woody tissues of various fruit trees. It typically attacks the bark and cambium, causing localized tissue necrosis that can lead to significant damage if the infection is left unchecked and the tree's health is already compromised.

The host range of Rugonectria rugulosa includes various pome and stone fruit trees, such as apples, pears, cherries, and plums. It is especially prevalent in orchards where trees have sustained prior injuries, such as pruning cuts, cracks caused by frost, or damages resulting from sunscald. The fungus exploits these points of entry to colonize the conductive tissues.

Symptoms of the infection include discoloration of the bark, which eventually becomes sunken and develops deep cracks. A key identifying feature is the presence of small, bright orange or reddish fruiting bodies (perithecia) that emerge through the bark surface. As the disease progresses, the bark may peel away, and twigs or branches may die back completely due to the disruption of nutrient flow.

Development of the fungus is highly dependent on environmental conditions, particularly high humidity and moderate temperatures. The spores are primarily dispersed by rainfall splashes, wind, and occasionally by bark-feeding insects. The pathogen survives the winter in infected bark tissues and debris, making it a persistent threat that can initiate new infections during the following growing season.

Management of the disease requires an integrated approach to minimize infection pressure. Recommended practices include:

• Sanitary pruning to remove and destroy infected wood promptly.
• Applying copper-based fungicides to pruning wounds and sites of infection.
• Improving orchard sanitation by removing all prunings and fallen debris.
• Protecting tree trunks with whitewash to prevent sunscald and frost cracks.
• Maintaining optimal tree vigor through balanced fertilization and proper water management.