Nectria ochroleuca

The fungus is characterized by the production of pale ocher to brownish perithecia, which serve as its sexual reproductive structures. These small bodies typically cluster on the surface of infected branches or bark.

Microscopically, the fungus produces ascospores which are essential for its life cycle and dispersal. These spores can persist in the environment, waiting for suitable hosts and moisture conditions to germinate.

It thrives in humid environments where moisture on the bark allows spores to infiltrate small fissures or wounds. The fungus colonizes the bark and cambium, eventually penetrating deep into the xylem tissue.

The taxonomic classification places it within the order Hypocreales. Its biology is adapted to exploit weakened plants, making it a opportunistic threat in orchards and forest nurseries.

This pathogen targets a wide variety of woody plants, including apple, pear, and various stone fruit trees. It is also known to cause significant damage to grapevine cultivars, impacting both yield and overall plant health.

Infection typically occurs through mechanical wounds, pruning cuts, or frost-damaged areas on the bark. Once inside, the fungus disrupts the transport of water and nutrients, leading to systematic decline.

In vineyards, the pathogen causes dieback of the cordons, often leading to total loss of individual vines. The affected wood becomes brittle, losing its structural integrity and ability to support heavy growth.

In fruit orchards, the fungus can lead to the death of entire branches or even the entire tree if the trunk becomes girdled by the necrotic lesion. This causes substantial economic losses to growers.

Young nursery stock is particularly vulnerable, as the pathogen can cause rapid dieback of grafted scions. Proper management in the nursery stage is crucial to prevent the spread of the infection to new orchards.

The most common sign of Nectria ochroleuca is the appearance of depressed necrotic spots on the bark. These lesions eventually grow, causing the bark to crack and peel, exposing the underlying dead wood.

During periods of high humidity, small ocher-colored cushions, representing the fungus's fruiting bodies, may emerge from the cracked bark. This is a definitive visual sign for identifying the presence of the pathogen.

Leaves on infected branches often show signs of chlorosis and wilt before dropping prematurely. This happens because the fungal colonization of the conductive tissues limits the tree's water uptake.

Exudation of gum from the infected site is a typical defensive reaction of fruit trees. However, this sap flow is usually insufficient to stop the spread of the fungal hyphae through the bark.

The internal wood of an affected branch typically shows dark brown staining, indicating decay. These areas are distinct from the surrounding healthy wood and represent the active zone of infection.

Sanitation is the most critical management practice. Infected branches must be pruned at least 10–15 cm below the visible lesion, and all pruning tools must be disinfected with alcohol or bleach between cuts.

Preventative measures include the use of copper-based sprays during the dormant season to cover potential entry points. Maintaining tree health through balanced fertilization and proper irrigation helps minimize susceptibility.

Protecting large pruning wounds with specialized sealants or paints is essential to block the entry of spores. Regular inspections of the orchard should be performed to catch early signs of infection.

If the infection is detected, the application of systemic fungicides can help slow down the progress of the disease. It is recommended to alternate different active ingredients to prevent the fungus from developing resistance.

All removed diseased plant material must be burned or destroyed far from the planting site. Leaving infected wood in the field acts as a continuous source of inoculum for the next season.