Spatial patterns suggest movement of the filbert bud mite (Phytoptus avellanae) between plants and overwintering infestations in a hazelnut (Corylus spp.) orchard

Phytoptus avellanae is an eriophyid mite that feeds on and damages the vegetative and floral buds of hazel ( Corylus ) species by forming galls that impact hazelnut yield. Phytoptus avellanae has been identified on hybrid hazels (European hazel, Corylus avellana × American hazel, Corylus americana ) that have been developed for hazelnut production in the eastern United States and Canada, but year-to-year variation in distribution and severity of P. avellanae damage within a field has not been studied. Additionally, whether P. avellanae differentially infests and damages the hybrid hazel plants vs. native Corylus americana plants is unknown. We assessed the spatial trends and species preferences of P. avellanae within a mixed-species field of hazels over a four-year period. All hazels were surveyed for galls caused by P. avellanae each spring and assigned a qualitative damage rating. We found that damage from P. avellanae was higher on hybrid hazel plants than on C. americana in each year of the study. In general, P. avellanae ratings increased towards the center of the field in most years. Our results showed that plants surrounded by infested neighbors often had higher damage ratings, suggesting that P. avellanae moves between adjacent plants. Understanding the within field distribution and host-plant preferences of P. avellanae will contribute to the development of scouting and management recommendations, provide insight on risk of mite movement between wild hazels and hybrid plantings in North America, and inform breeding efforts for this harmful pest.