Oregon produces over 99% of the hazelnuts (Corylus avellana) grown in the United States, representing 4% of worldwide production in 2019. Filbertworm (Cydia latiferreana) is the key economic pest of hazelnuts in the Pacific Northwest and accounts for a major source of pesticide use, especially for organic producers. Oregon white oak (Quercus garryana) is a native host for filbertworm, and oak woodlands can maintain source populations that re-infest orchards. This makes native oak habitat, which has been reduced over 95% since the 1800’s, a liability to hazelnut producers. The majority of Oregon’s remnant oak woodlands are on private agricultural land and this critical habitat is more threatened than ever. We conducted a two-year study investigating whether grazing domesticated pigs (Sus domesticus) can reduce filbertworm abundance in an Oregon white oak woodland and adjacent hazelnut orchard. Pigs have historically been used to glean fallen fruit from orchard floors and are efficient woodland grazers. If pigs effectively remove infested acorns, they can break the filbertworm life-cycle, reducing pest pressure, and make oaks an asset rather than a liability to diversifying farms.
Results/Conclusions
After Fall grazing, we found significantly lower filbertworm emergence from the leaf litter and infestation of acorns in grazed oak pastures. These results support our hypothesis that: grazing pigs in oak woodlands reduces filbertworm abundance by interrupting its life-cycle, primarily by the removal of infested acorns on the forest floor. Indigenous cultures historically controlled filbertworm with periodic burning, and pig grazing could be simulating this in some ways. It is, however, important to note that there is great concern over the management of pigs within woodlands, as feral-hog populations are known to cause environmental degradation across the United States. It is our recommendation this application be scaled, duplicated, and repeated within a more mature hazelnut orchard; meanwhile careful attention should be made to grazing duration and intensity. Since these oak woodlands evolved with fire, vegetation thinning by prescribed burns in conjunction with grazing may alleviate some vulnerability from competitive exclusion by other trees, reduce wild population susceptibility, increase grazing efficacy, and potentially mitigate invasive species.