Nectria mammoidea

The fungus is characterized by the production of small, bright red or orange-colored perithecia, which develop in clusters on the bark of infected branches, especially under humid conditions.

The life cycle of the pathogen involves both asexual (conidial) and sexual stages, which allow it to propagate efficiently and survive in host tissues throughout the year.

As a facultative parasite, Nectria mammoidea can inhabit dead organic matter as a saprotroph and switch to an aggressive parasitic lifestyle when it finds weakened tree tissues.

It survives winter periods within the infected host bark, forming resistant structures that trigger new infections once the environment becomes conducive for growth in the spring.

The pathogen impacts a wide range of deciduous hosts, including important fruit trees such as apple and pear, as well as various forest species like beech and maple.

Infection primarily occurs through wounds caused by pruning, winter frost cracks, hail, sunscald, or activities of wood-boring insects, which create entry points for fungal spores.

Once established, the fungus causes localized necrosis. As the infection expands, it can girdle branches or trunks, effectively cutting off the nutrient supply and causing branch dieback.

In cases of severe infestation, especially in young saplings, the damage can lead to the total death of the plant, while mature trees may suffer significant loss of canopy.

Environmental stress, such as drought or poor site selection, exacerbates the damage caused by the pathogen, as the tree's natural defense systems are compromised.

Early symptoms appear as depressed areas or lesions on the bark, which gradually darken as the cambium and underlying tissues begin to necrotize and die.

The most distinctive visual sign is the emergence of small, nipple-shaped (mammoid) fungal fruiting bodies on the bark surface, providing the species with its specific epithet.

Cracks often develop along the edges of the infected bark, exposing the inner wood which eventually becomes discolored, decayed, and increasingly fragile due to the fungal activity.

The foliage on branches affected by ring necrosis will show signs of yellowing and wilting, eventually leading to premature defoliation as the branch dies off completely.

During wet weather, the surface of the lesions may display powdery spore masses, indicating active sporulation and the high risk of further spread within the canopy.

The primary control strategy involves rigorous orchard sanitation, including the prompt removal and destruction of infected branches to reduce the amount of inoculum present.

Any necessary pruning cuts must be made with clean tools and immediately sealed with wound-dressing fungicides to prevent opportunistic spore colonization of the fresh wood.

Maintaining tree vigor through proper fertilization, adequate irrigation, and effective pest management is crucial to allow the tree to naturally resist infection attempts.

Proactive measures, such as painting trunks with protective coatings or using copper-based fungicides, can significantly lower the risk of infection through bark fissures.

• Strict removal and disposal of all infected woody debris from the site.
• Application of preventative fungicide sprays during dormancy and early growth phases.
• Protection of trunks against sunscald and mechanical bark injuries.