Optimizing soil applications of entomopathogenic fungi and nematodes to enhance efficacy against plum curculio larvae in upper midwest tree fruit production

The plum curculio (Conotrachelus nenuphar Herbst) remains a key concern of tree fruit growers facing limitations on pesticide inputs largely brought on by the passage of the Food Quality Protection Act (1996). Prior research has demonstrated the virulence of entomopathogenic nematodes and fungi to different plum curculio life stages, including 4th instar larvae. Previous field experimental efforts demonstrated that the entomopathogens Beauveria bassiana and Steinernema riobrave targeting larval plum curculio life stages suppressed adult emergence with limited efficacy across entomopathogen application timings. Microclimate, including soil moisture and texture, was suspected to have affected efficacy. In 2011, we investigated the effect of soil moisture and texture on the efficacy of entomopathogenic fungi and nematodes targeting plum curculio larvae in Michigan orchards. Soils were collected from three orchards, representative of soils found in major tree fruit producing regions of Michigan, containing differing amounts of sand, clay, and loam. Microjet sprinklers were installed in pre-existing irrigation hoses located within the driplines of trees and irrigated soils for one hour -1, 0, 1, 3, and 5 d from applications of B. bassiana and S. riobrave.