Extrafloral nectaries (EFNs) in many plant species produce sugary secretions that commonly attract ants. This research determined the impact of peach (Prunus persica L. Batsch) EFNs on the biological control of the oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a key economic pest in peach orchards, and studied interactions of EFNs and ants. Studies (2002–2005) in peach orchards of the mid-Atlantic United States showed that ‘Lovell’ peach trees with EFNs supported more parasitic Hymenoptera in the spring and increased the parasitism of G. molesta larvae later in the season than those trees without EFNs. Ant exclusion experiments revealed that trees with EFNs harbored fewer G. molesta larvae when ants were permitted access to the tree canopies. Furthermore, the trees with EFNs had ≈90% less fruit injury by G. molesta, indicating that EFNs have a protective role for the fruit as well. The results show that the combined actions of ants and parasitic Hymenoptera confer an EFN-mediated protective effect spanning the whole fruit growing season. When EFNs are present, naturally occurring biological control agents can reduce damage by G. molesta in peach orchards without insecticide inputs. The EFNs are an important host-plant characteristic that should be retained in future peach cultivar selections as a means of enhancing biological control.