Use of Entomopathogenic Nematodes (Steinernematidae) in Conjunction with Mulches for Control of Overwintering Codling Moth (Lepidoptera: Tortricidae)

Abstract

Mulches were compared to test their utility for enhancing efficacy of entomopathogenic nematodes (EPNs) applied against over-wintering codling moth, Cydia pomonella (L.), larvae. Compared with bare ground, mulches may enhance control by providing cocooning sites for codling moth larvae and a substrate that is easy to treat, maintains moisture, and enhances nematode activity. Steinernema carpocapsae (Weiser) or S. feltiae (Filipjev) were applied at a rate of 2.5 × 109 infective juveniles (IJs)/ha against cocooned sentinel codling moth larvae in cardboard strips followed by 2 h of irrigation in plots that were covered with one of four mulches (clover, shredded paper, grass hay or wood chips) or to bare plots on 29 September 2003. Average mortalities of 97 and 98% were observed in paper-mulched plots treated with S. carpocapsae or S. feltiae IJs, respectively, compared to 80 and 76% mortality in bare plots. Larvicidal activity for S. feltiae against sentinel larvae in cardboard strips that were placed in crevices in the soil was nearly identical in all mulched and bare plots (97–100% mortality), but reduced for S. carpocapsae in wood chip and clover plots (76–79% mortality) relative to paper, grass hay and bare plots (93–97% mortality). A significant portion of sentinel larvae (25 and 14%) that were placed in crevices in the soil in hay- and paper-mulched control plots revealed the natural presence of EPNs (Heterorhabditis sp.). Applications of S. carpocapsae and S. feltiae at a reduced rate of 109 IJs/ha on 20 April 2004, followed by 1 h of irrigation resulted in 13.1 and 7.4% reduction in sentinel larvae in bare plots compared to 36 and 62% in mulched plots, respectively. Applications of S. carpocapsae and S. feltiae at a rate of 2.5 × 109 IJs/ha on 21 September 2004 to bare and wood chip-mulched plots followed by 1 h of irrigation resulted in 21 and 65% reduction in sentinel larvae in bare plots compared to 93 and 85% in mulched plots, respectively. Residual larvicidal activity of EPNs 3 d after applications in treated plots was low, but significant in the nonmulched plots (12–17% mortality) relative to untreated controls (1–2% mortality).