Use of steinernematid nematodes for post harvest control of navel orangeworm (Lepidoptera: Pyralidae, Amyelois transitella) in fallen pistachios

Four trials employing 1-m2 plots were conducted between November 2002 and April 2003 in Madera County, California, to evaluate the ability of two species of nematodes, Steinernema carpocapsae and Steinernema feltiae, to control navel orangeworm, Amyelois transitella, in infested pistachios on the ground. The plots were located in two 16.2 ha blocks of pistachio trees planted in sandy loam soil. A total of 4300 larvae were recovered from 17,593 laboratory-infested pistachios (24.4% average infestation). Nematodes were applied with a backpack sprayer at concentrations ranging from 50,000–1,000,000 infective juveniles (IJs)/m2 (100,000 IJs/m2 was assessed in all four trials) and an application rate of 374 or 500 ml/m2 water. S. carpocapsae was more effective than S. feltiae in pistachios and produced >72% mortality at a concentration of 100,000 IJs/m2 when nighttime temperatures were above freezing. S. carpocapsae was equally effective in bare and leaf-covered plots and persisted longer in sandier soil (8 weeks) than S. feltiae. S. carpocapsae has the potential to multiply in the field; 51.3% of the cadavers examined 21 days after application contained developing nematodes (n=226). Our trials demonstrated that S. carpocapsae can play a role in the post harvest control of navel orangeworm and that the formulation tested produced greater mortality than the formulations of S. feltiae tested at the same concentration.