Measuring field efficacy of Steinernema feltiae and Steinernema riobrave for suppression of plum curculio, Conotrachelus nenuphar, larvae

The plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruit. Our objective was to determine the ability of Steinernema feltiae and Steinernema riobrave to control C. nenuphar larvae in soil. Nematodes were applied at 100 infective juveniles/ cm in peach orchards at two locations (Byron, GA and Quincy, FL) in 2002 and 2003. Treatments were compared to an untreated control and, in Byron only, application of imidacloprid. Two methods of evaluation were used to test efficacy; in Byron, 50 (2002) or 100 (2003) larvae were buried in plots 3 days prior to treatment applications, whereas in Quincy, larvae entered the soil from 100 naturally infested peach fruits placed in each plot prior to treatment. Treatment efficacy was based on average number of adults emerged/plot (captured in wire cone cages). In all trials (regardless of method), S. riobrave was the only treatment that caused a significant reduction in weevil emergence. S. riobrave applications resulted in greater than 97% C. nenuphar control in two out of three trials, and 77.5% control in the fourth trial. The lower level of control in the fourth trial was likely due to a prolonged period of larval exit from infested fruit into soil and lower temperatures during this period. Timing applications in accordance with pest phenology and environmental conditions appear to be critical in achieving high levels of efficacy. The observed high levels of C. nenuphar control by S. riobrave are intriguing and justify further studies. Published by Elsevier Inc.