The pecan weevil, Curculio caryae (Horn), is a key pest of pecan in North America. Entomopathogenic nematodes have potential as alternative control agents for C. caryae. In prior studies, when single applications of entomopathogenic nematodes were applied during adult weevil emergence, only moderate efficacy was observed. The objective of this study was to determine the compounded impact of multistage nematode applications on C. caryae mortality over a 2-year period. Experiments were conducted in a pecan orchard in Byron, GA. In the fall of 2007, freshly-emerged C. caryae larvae were placed in pots under the tree canopy. The nematode, Steinernema carpocapsae (Weiser), was applied 3 times in spring through fall of 2008 (targeting C. caryae larvae) and 3 times during the spring and summer of 2009 (primarily targeting adults). The percentage of surviving C. caryae was determined in the fall of 2008 and 2009, approximately 1 and 2 years after larvae emerged. In 2008 (1 year postemergence), the number of surviving C. caryae was significantly less in treated pots (3.75%) compared with untreated pots (7.38%). In 2009 (2 years postemergence), the number of surviving C. caryae was reduced further and was significantly less in treated pots (0.5%) compared with untreated pots (2.63%). When corrected for natural mortality, after 2 years the nematode treatments provided 81% control. These results indicate promise for reducing the weevil below economic levels through repeated multistage applications of S. carpocapsae. In future research, the approach will be tested on an orchard scale, and nematode application rates and timing will be optimized.
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