Evaluation of entomopathogenic nematodes to manage root weevil larvae in Washington State cranberry, strawberry, and red raspberry

Abstract

The ability of entomopathogenic nematodes to reduce abundance of subterranean root weevils was evaluated in three small fruit crops of Washington State. In cranberry, the entomopathogenic nematodes Steinernema carpocapsae (Weiser) and S. glaseri Steiner applied at 30 IJ (infective juveniles) per square centimeter reduced abundance of black vine weevil, Otiorhynchus sulcatus (F.), by 96 or 100% respectively compared with the untreated control. According to a waxmoth [Galleria mellonella (L.)] bait bioassay, S, carpocapsae persisted at higher levels than S. glaseri (0.48 versus 0.04% infested waxmoth per applied infective juvenile at 30 d after treatment) and for a longer interval (at least 60 d after treatment), but neither species dispersed beyond the treatment plots. At one of two strawberry sites, S. carpocapsae and Heterorhabditis marelatus Liu OH10 significantly reduced the abundance of black vine weevil (all stages) and pupal strawberry root weevil, O, ovatus (L.), compared with the untreated control. The same treatments were applied at the other site, but only pupal black vine weevils were significantly affected. Neither S. carpocapsae nor H. bacteriophora Poinar significantly reduced the abundance of black vine weevil in two trials conducted in red raspberry. Entomopathogenic nematodes were recovered from larval waxmoth Galleria mellonella balis placed on soil from the red raspberry sites 6 wk after treatment. Efficacy of entomopathogenic nematodes in all trials was likely most limited by cool soil temperatures that are typical to Pacific Northwest small fruit crops during spring when root weevils are in late larval and pupal stages, but soil structure and crop characteristics, particularly dense strawberry foliage and large crowns, were also important.