Codling moth (Lepidoptera: Tortricidae) control on commercial walnuts with a granulosis virus

Commercially produced, experimental lots of codling moth, Cydia pomonella (L.), granulosis virus (CMGV) formulations were field-tested for control of codling moth larvae on commercial walnuts. Because it has little or no effect on beneficial species and probably would not disturb the control of the walnut aphid, Chromaphis juglandicola (Kaltenbach), by the parasite Trioxys pallidus (Haliday), CMGV was evaluated in 1980-1983 in Kings, Tulare, and Yolo counties in California. In 1980, control of codling moth by CMGV was similar to that of conventional insecticides (e.g., 80%). However, a maximum of 60% control was obtained in 1982. The level of control obtained in 1982 was lower than that suggested by the residue studies. In 1983, control was equivalent to that of a chemical insecticide standard, but control depended upon application timing. Field persistence of the virus was sufficient, to cause 90% larval mortality immediately after application and 80% mortality 5 d later. The addition of several concentrations of skim milk did not increase persistence. It was concluded that timing of CMGV applications to coincide with egg hatch and field persistence of formulations are critical to control of codling moth on walnuts