European fruit tree canker

The fungus Nectria ditissima is the primary causal agent of the disease known as European canker or Nectria canker. It is an ascomycete fungus that infects the bark and cambium of trees, causing localized necrosis and the subsequent formation of sunken or open lesions on branches and trunks.

This pathogen primarily targets pome fruit trees, with apple and pear trees being the most susceptible. However, it can also infect a variety of broad-leaved deciduous trees, such as beech, ash, and maple, which act as alternative hosts and reservoirs for the fungus within the landscape.

Infected trees display distinct symptoms, ranging from small, discolored bark patches to deep, perennial cankers. These lesions often exhibit concentric ridges of callus tissue formed by the tree's attempt to compartmentalize the infection. During moist conditions, small, bright red or dark-colored fruiting bodies, known as perithecia, emerge on the canker surface to release spores.

The development and spread of Nectria ditissima are heavily influenced by environmental conditions, particularly high humidity and rainfall. The fungus enters the plant tissue through natural openings or mechanical wounds, such as pruning cuts, leaf scars, or frost damage. Spores are dispersed primarily by rain splash and wind, making wet autumns and springs high-risk periods for new infections.

The damage caused by this disease is severe, as it leads to twig dieback, branch girdling, and eventually the death of the entire tree if the main trunk is affected. Management strategies must be multifaceted:

• Removing and burning infected wood during dry weather.
• Painting pruning wounds with protective sealants.
• Applying copper-based fungicides during leaf fall or early spring.
• Selecting resistant cultivars for new orchard plantings.