Efficacy and persistence of Steinernema carpocapsae (Rhabditida: Steinernematidae) applied through a center-pivot irrigation system against larval corn rootworms (Coleoptera: Chrysomelidae)

We evaluated control of natural and artificially infested populations of larval corn rootworms (Diabrotica virgifera virgifera LeConte and D. barberi Smith Lawrence) in corn (Zea mays L.) treated with entomopathogenic nematodes, Steinernema carpocapsae (Weiser); All strain, applied after planting through a center-pivot irrigation system at 2.5 and 1.2 X 10(9) infective juvenile nematodes per hectare. We compared control achieved with nematodes with that achieved with planting time applications of terbufos (Counter 15G [granular]; 9.9 kg [AI]/ha) and chlorpyrifos (Lorsban 4E [emulsion]; 1.12 kg [AI]/ha) applied after planting through an irrigation system, and with an untreated (water only) control. In 1989 studies with natural rootworm populations, chlorpyrifos and both nematode rates provided significantly lower root damage ratings than terbufos and the untreated control. Chlorpyrifos was significantly more effective than the low nematode rate. In 1990 studies with a natural rootworm infestation, the high nematode rate, terbufos, and chlorpyrifos provided significantly lower root damage ratings than the untreated control. Effectiveness of the low rate of nematodes was not significantly different from that of the untreated control. In both years, all treatments were generally less effective under higher rootworm pressure in artificially infested plots. In 1989, the high rate of nematodes significantly reduced adult western corn rootworm emergence compared with terbufos, the low rate of nematodes, and the untreated control. In 1990, all treatments significantly reduced western corn rootworm adult emergence compared with the untreated control. In 1989, viable nematodes were commonly found 1-3 d after application and at low levels 28 d after application. However, in 1990, no viable nematodes were found > 7 d after application.