| Summary: | Extensive collar rot, sunken and bleeding cankers, shoot blight, and fruit rot symptoms on olive trees have recently been observed in several orchards in Italy. Since there is little information about the etiology of these diseases and given the high economic relevance of this iconic crop, a study was conducted from autumn 2017 to summer 2022, in four Italian regions, to define the occurrence, distribution and impact of the main pathogens involved. A total of 1064 symptomatic olive samples were collected and processed. Based on colony appearance, micromorphological analysis and DNA sequence data, thirty-eight species, including eighteen <i>Botryosphaeriaceae</i> species belonging to five genera and fifteen <i>Phytophthora</i> species, were isolated and identified, thirteen of which, <i>Diplodia africana</i>, <i>D. fraxini</i>, <i>D. subglobosa</i>, <i>Dothiorella omnivora</i>, <i>Do. sarmentorum</i>, <i>Do. sempervirentis</i>, <i>Sardiniella urbana</i> (<i>Botryosphaeriaceae</i>), <i>Phytophthora cactorum</i>, <i>P. cinnamomi</i>, <i>P. citricola</i>, <i>P. crassamura</i>, <i>P. niederhauserii</i> and <i>P. pseudocryptogea</i>, are reported here for the first time in olive trees. Pathogenicity tests performed on unripe drupes and on potted olive seedlings completed Koch postulates and highlighted that several species of <i>Botryosphaeriaceae</i> and <i>Phytophthora</i> represent a growing threat to olive trees.
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