Field efficacy of entomopathogenic fungi and nematodes targeting caged last-instar plum curculio (Coleoptera: Curculionidae) in Michigan cherry and apple orchards.

The plum curculio (Conotrachelus nenuphar Herbst) is a key pest of pome and stone fruit in eastern North America. We tested the efficacy of five pathogens over the course of three seasons in 10 Michigan apple and cherry orchards, with introductions of larvae to caged pots containing pathogen-treated soil. The nematode Steinernema riobrave was the most effective pathogen in the 2 yr it was tested, but only in soils with the highest sand content (81-88%) and when it was applied 1 h or 5 d after last instars of plum curculio. S. carpocapsae in an organic formulation was less effective, but significantly reduced plum curculio emergence in 1 yr of the study when applied 3 d before C. nenuphar larvae were introduced. Beauveria bassiana was effective in only 1 of the 3 yr it was tested, only in soils with lower sand content, and only when it was introduced within 1 h of plum curculio larvae. Metarhizium anisopliae and Heterorhabditis bacteriophora were ineffective. Michigan orchards may require sprinkler irrigation coupled with precise timing recommendations and oviposition monitoring to enhance entomopathogen application efficacy against soil-dwelling last instars.