|Abstract or Summary
- Black vine weevil (BVW), Otiorhynchus sulcatus Fabricius, is a serious pest in cranberry, Vaccinium macrocarpon. Larvae feeding below the soil surface cause damage to the roots and underground stems. Knowledge is sparse in regard to the damage potential of BVW in Pacific Northwest cranberry beds. Control with insecticides is limited by inefficacy, environmental contamination of runoff water, and negative effects on pollinators and other non-target organisms. The objectives of this study were two-fold: (1) to determine the relationship between initial BVW egg density and the effect of subsequent larval damage on cranberry plant health and (2) to compare the efficacy and persistence of Metarhizium anisopliae (Sorokin), Steinernema kraussei (Steiner), and the systemic neonicotinoid imidacloprid to control
BVW in cranberries. Two varieties of potted cranberry vines were infested with six BVW egg densities. Root damage and canopy health was assessed, both continuously and destructively. Greater root damage, lower total shoot length, lower shoot weight and decreased water use were associated with increased egg density. More root damage was observed in 'Stevens' compared to 'McFarlin'. Percent green leaf area was also significantly reduced with increasing BVW egg densities. Results indicate that increased BVW egg densities decrease plant health by increasing subsequent larval damage to the roots. This damage induces drought stress, reduces the amount of photosynthetic tissue in the canopy and limits shoot growth.
To address the second objective, treatments were applied to cranberry beds at two field sites and soil was collected by treatment on five dates during 2009 and 2010. Soil samples were then inoculated with laboratory-reared BVW larvae and incubated at 20°C to assess potential control by, and persistence of, each treatment in the cranberry soil. Steinernema kraussei did not result in significant BVW mortality either by site or sample date. Imidacloprid resulted in significant mortality only in Langlois, Oregon and only on the first sample date. Metarhizium anisopliae provided inconsistent results. In Long Beach, Washington, M. anisopliae caused significantly higher mortality than any of the other treatments on three of the five sample dates. In Langlois, M. anisopliae caused significantly higher mortality than the control only on the last sample date, one year after treatment application. However, average mortality over the entire sampling period indicated that M. anisopliae was more effective than either S. kraussei or imidacloprid in both locations.