Ash phomopsis

The disease is caused by the fungus Diaporthe scobina, a member of the ascomycetes class. This pathogen is responsible for necrotic lesions and stem cankers, primarily targeting tree species within the Fraxinus (ash) genus. It represents a significant threat to nurseries and established forest stands alike.

The fungus affects various ash species, with the infection typically entering through wounds, pruning cuts, or natural bark fissures. Once established, the pathogen colonizes the bark and cambium layers, systematically disrupting the tree's vascular system, which leads to the decline of distal branches.

Key symptoms include the development of depressed, discolored necrotic areas on the bark. As the fungus progresses, these areas crack open and form cankers. A defining feature is the appearance of small, dark, pimple-like structures known as pycnidia on the surface of dead bark, which serve as the primary source for further spore dispersal.

The development and spread of Diaporthe scobina are highly dependent on environmental conditions, specifically high humidity and moderate temperatures. Spores are primarily disseminated by rain splashes and wind currents during the growing season. Trees stressed by drought or poor site conditions are significantly more susceptible to successful colonization.

The impact of this disease ranges from reduced aesthetic value in urban settings to severe dieback and mortality in young forest plantations. Effective management strategies focus on integrated approaches: physical removal of diseased branches, sanitation through the destruction of infected debris, and the application of protective fungicides during periods of high spore activity to prevent new infections.