The investigation into aspects of quality and condition of European hazelnut fruit produced in Chile is an aspect that has yet not been studied in any great detail. The literature in Chile records various alterations in the seed, such as double fruits, vain fruits, brown cavities, and fungi (Aspergillus niger, Alternaria alternata, Trichothecium roseum). In order to determine inoculum sources, it was necessary to assess the incidence of postharvest fungi on the vegetative and reproductive structures of European hazelnut, 'Barcelona' and 'Tonda di Giffoni', grown on commercial plantations in the Araucanía region. Tissue samples were kept in a wet chamber and fungi isolates were made in acidulated malt agar medium. The identification of Trichothecium roseum was based on morphometric characterization and corroborated by the CABI (IMI 500172). T. roseum developed profusely when it was inoculated in the hazelnut seeds of both cultivars; the incidence with 21 days in a wet chamber was as follows: branches (24.5%), vegetative buds (30.9%), leaves (5.7%), male flowers (36.4%), female flowers (28.2%), pericarp (30%), and seeds (21.4%). In hazelnut seeds of the 'Barcelona' cultivar inoculated with the conidia (1×106) of T. roseum, a significant increase in acidity (1.79) was detected compared to the control (0.55); in the case of the peroxide index (0.73) the variation was less intense (control 08.0). The referential value was 1% acidity and a peroxide index of 0.5%. The high incidence of T. roseum in catkins and glomeruli constitutes an inoculum source for the seed and, as a result, a deterioration in the postharvest quality and condition, with a risk for the consumer due to mycotoxins. This situation means control strategies must be developed, particularly during the flowering period.