Hazelnut (Corylus avellana L.) is a key crop in the Mediterranean basin, particularly in Turkey and Italy, which account for most of the global production. Phytoptus avellanae(Eriophyoidea: Phytoptidae) is a major pest causing bud gall formation and severe yield losses under high infestation levels. A recently recognized free-living form within the species complex (still undescribed) may also damage additional plant organs, further increasing its economic impact. This study assessed the efficacy of commercial biopesticides based on the arthropod-pathogenic fungi (APF) Beauveria bassiana and Akanthomyces muscarius as low-impact control tools against P. avellanae sensu lato. Laboratory and field trials were conducted using commercial fungal formulations applied at label-recommended doses. Specific protocols were developed for both experimental conditions. Laboratory assays were performed during winter 2023/2024, winter 2024/2025, and spring 2025 in two separate laboratories under standardized experimental conditions. In 2024, a field trial was conducted in a commercial orchard using the same fungal products. In laboratory assays, bud galls were disinfected, dissected, immersed for 30 s in aqueous suspensions of the fungal products or water (control), dried under a laminar-flow hood, incubated for seven days, and subsequently examined to assess mite mortality. Intermediate observations were also recorded. In the orchard trial, buds and nuts were immersed in the same fungal suspensions without detachment from the plant. Two weeks after application, treated plant organs were collected and examined to determine mite mortality. In laboratory assays, B. bassianainduced significantly higher mite mortality compared to the control. Fungal infection was confirmed by culturing on growth medium and by microscopic examination of slide-mounted infected mites. In field trials, plant organs treated with B. bassiana showed higher mite mortality than controls for both buds and nuts. Overall, both B. bassiana and A. muscariusdemonstrated promising efficacy in controlling P. avellanae, supporting their potential inclusion in integrated pest management programs. These findings support the potential integration of arthropod-pathogenic fungi into sustainable management strategies for P. avellanae, contributing to reduced reliance on conventional chemical control.