Phytocoptella avellanae and Cecidophyopsis vermiformis are microscopic eriophyid mites that cause damage to developing hazelnut buds and are commonly referred to as “big bud mites”. Damage caused primarily by P. avellanae manifests as enlarged, split buds termed “blasted buds” or “big buds”. To date, broad-spectrum acaricides are often sprayed on a calendar basis, or when trees appear to have numerous blasted buds; however, this approach may not be entirely effective if applications do not coincide with bud mite migration, when adults and juveniles are most exposed to residues. This migratory period varies with environmental conditions and currently there are no definitive guidelines delineating the optimal time to spray for bud mites in the Pacific Northwest (PNW). Traps can be used to estimate when the migration occurs, but are very labor intensive and are not often utilized by growers. A predictive phenology model to guide management should be possible, and our goal is to generate the necessary data. We collected phenology data from 2016-2020 to develop a migration curve. In addition to investigating a migration curve, we also tracked the fate of developing blasted buds over the course of the 2020 field season. An initial evaluation of blasted buds was conducted in early spring, when damage symptoms first appear, and a follow up observation was conducted in early fall to evaluate the trees’ ability to overcome damage.
