Laboratory and Field Bioassays of Arthropod Pathogenic Fungi Application for the Control of the Hazelnut Big Bud Mite, Phytoptus avellanae s. l

Phytoptus avellanae is a key hazelnut pest, causing the swelling of mixed buds during the autumn–winter period and a compromised nut yield. This study aimed to evaluate the effectiveness of commercial biopesticides based on Beauveria bassiana and Akanthomyces muscarius in controlling this pest. Specific laboratory and field protocols were developed. In the laboratory, bud galls were disinfected, dissected, immersed for 30 s in a water suspension of the products and in water (control), dried in a laminar flow hood, incubated for 7 days and inspected to assess mite mortality. Intermediate observations were also recorded. Significantly higher mortality was recorded in the treatment with B. bassiana. Infection with B. bassiana was confirmed by a culture in medium and slide-mounting of infected mites. The orchard assay was performed by immersing buds and nuts in the fungal suspensions applied in the laboratory without separating any organ from the plant. Two weeks after application, the treated plant organs were removed and examined to assess mite mortality. The organs treated with B. bassiana showed higher mite mortality than the control for both buds and nuts. Treatments with arthropod pathogenic fungi appear to be promising for inclusion in the control strategy of P. avellanae.