The 'copper walnut blight' or 'thousand-cancer disease' is a plant disease caused by the ascomycete fungus Geosmithia morbida, which is transmitted to the plant by the adult of the scolythid insect Pityophthorus juglandis, which, by piercing the bark of walnut plants in order to lay its eggs, acts as a vector spreading the disease. The coexistence of the pathogen and its vector is therefore necessary for the symptoms of this disease to manifest.
By virtue of their limited spread and the high presence of susceptible hosts on the European continent, Geosmithia morbida and Pityophthorus juglandis are included in the list of quarantine pests known to occur in the territory of the European Union (Annex II, Part B, Implementing Regulation (EU) 2019/2072).
