1. Entomopathogenic nematodes for control of overwintering codling moth in orchards L. A. Lacey, H. L. Headrick, S. P. Arthurs and T. R. Unruh USDA-ARS, Yakima Agricultural Research Laboratory, Wapato, WA Codling moth, Cydia pomonella, is the most serious insect pest of apple in the Pacific Northwest. In conventional orchards, the traditional method for controlling this pest is through the routine application of broad spectrum insecticides. Options for codling moth control for organic growers have been limited to methods such as oils, trapping, mating disruption, and manual removal of infested fruit. Entomopathogenic nematodes (EPNs) targeted for overwintering stages of the moth and the codling moth granulovirus targeted for neonate larvae offer the potential for a double-pronged strategy for controlling this pest. The overwintering stage of codling moth, cocooned larvae within hibernacula, is a difficult stage to kill using most conventional approaches. In the fall and winter, this stage represents the entire population and is virtually a captive audience if an effective means of control could be harnessed against it. The elimination or reduction of the codling moth at this time would provide significant protection to fruit early in the following growing season. Since 1997 the USDA-ARS-Yakima Agricultural Research Laboratory has conducted several trials of EPNs to determine their most effective application strategy to control overwintering codling moth in orchards and fruit bins. We have found EPNs to be effective in controlling overwintering cocooned larvae of codling moth under a variety of conditions if the habitat or bin is kept moist for 6 to 8 hours and temperatures are 60ºF and above (Lacey et al., 2005a and 2005b; Unruh and Lacey, 2001). Maintenance of moisture after application of the nematodes using irrigation in orchards has been especially successful in trellised apple orchards and older pear orchards. Sustained moisture that was favorable for nematode survival is enhanced in orchards where mulch (shredded paper, hay, wood chips, or clover) is placed beneath trees. In this poster we present the highlights of studies conducted on EPNs for codling moth control from 1999 to 2004. METHODS, RESULTS and DISCUSSION Field trials with Steinernema carpocapsae and S. feltiae were conducted in apple and pear orchards to determine the effects of seasonal temperatures, adjuvants, post-application irrigation and method of application on control of cocooned CM larvae. In studies conducted in late summer, fall and early spring (1999-2000), EPNs were applied to apple trees (Golden Delicious) with a backpack sprayer at a rate of 10 6 infective juveniles (IJs)/tree plus supplemental wetting to aid survival of IJs. Good control by both EPN species was observed in September (94-95 % mortality in sentinel CM larvae) (Fig. 1). In October, control by S. feltiae was also effective (90 % mortality), but S. carpocapsae was less effective (58% mortality), ostensibly due to the cooler conditions. In identical applications the following spring, the efficacy of S. carpocapsae and S. feltiae was reduced during cool windy conditions in March 30 tests, providing 26% and 65% control of sentinel larvae, respectively, but improved during warmer conditions in April 12 tests (71 and 86% control, respectively). In further tests in the same location in mid-October 2001, S. feltiae (10 6 IJs/tree) were most effective for control of sentinel CM larvae cocooned in cardboard strips (≈ 80% mortality) and logs (34-47%) when combined with a wetting agent (Silwet L77®) or a humectant (Stockosorb®) and the trees were misted for 4 h post-treatment. In the absence of post-application wetting, the addition of either adjuvant (Silwet and Stockosorb) to IJs also increased larval mortality in strips, although it did not significantly improve nematode efficacy on logs. In another test in late summer 1999, the use of a lance applicator (applying 2.0 × 10 6 IJs/tree) did not significantly improve control of cocooned larvae for either EPN species, when compared with a tractor- mounted airblast sprayer (Fig. 2). Two further tests in the fall of 2003 with S. carpocapsae and S. feltiae compared post-application wetting with existing and modified irrigation in 4-year-old trellised apple (Gala) and established Bartlett pear orchards. No significant improvements in sentinel larval mortality were observed following application of both EPN species with an airblast sprayer (1 – 2.5×10 9 IJs/ha) when conventional overhead rotator sprinklers were replaced with lower volume microsprinklers. REFERENCES CITED Lacey, L. A., S. P. Arthurs, T..R. Unruh, H. Headrick and R. Fritts, Jr. 2005a. Entomopathogenic nematodes for control of codling moth (Lepidoptera: Tortricidae) in apple and pear orchards: effect of nematode species and seasonal temperatures, adjuvants, application equipment and post-application irrigation. Biol. Contr. in press. Lacey, L. A., D. Granatstein, S. P. Arthurs, H. L. Headrick and R. Fritts, Jr. 2006. Use of mulches to improve the efficacy and persistence of entomopathogenic nematodes (Steinernematidae) for control of overwintering codling moth (Lepidoptera: Tortricidae). J. Entomol. Sci. accepted. Lacey, L. A., L. G. Neven, H. L. Headrick, and R. Fritts, Jr. 2005b. Factors affecting entomopathogenic nematodes (Steinernematidae) for the control of overwintering codling moth (Lepidoptera: Tortricidae) in fruit bins. J. Econ. Entomol. 98: in press. Unruh, T. R. and L. A. Lacey. 2001. Control of codling moth, Cydia pomonella (Lepidoptera: Tortricidae) with Steinernema carpocapsae: effects of supplemental wetting and pupation site on infection rate. Biol. Contr. 20: 48-56. Figure 1. The effect of seasonal temperature on mortality of cocooned codling moth larvae on Golden Delicious trees treated with two nematode species at one million IJs per tree. Data show (A) temperature range for the 8 h post-application and (B) average mortality for six tree plots. Symbols denote significant differences between nematode species. Mortality of untreated control larvae did not exceed 5.3% on any date. Figure 3. Evaluation of Steinernema carpocapsae and S. feltiae (1 billion IJs/acre) on bare ground and in plots with wood chip mulch, Fall 2004. Mulches were compared to test their utility for enhancing efficacy of entomopathogenic nematodes applied against overwintering codling moth 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 and which maintains moisture which enhances nematode activity. Steinernema carpocapsae or S. feltiae were applied at a rate of 2.5 x 10 9 infective juveniles (IJs)/ha against cocooned sentinel codling moth larvae followed by 2 h of irrigation in plots that were covered with one of four mulches (clover, shredded paper, hay or wood chips) or to bare plots on September 29, 2003. Average mortalities of 97 and 98%, respectively, in paper-mulched plots treated with S. carpocapsae or S. feltiae IJs was observed compared to 80 and 76% mortality, respectively, in bare plots. Larvicidal activity for S. feltiae against sentinel larvae 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, hay and bare plots (93-97% mortality). Applications of S. carpocapsae and S. feltiae at a reduced rate of 10 9 IJs/ha on April 20, 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 x 10 9 IJs/ha on September 2, 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 (Fig. 3). Residual larvicidal activity of EPNs 3 days after in applications in these plots was low, but significant. In many orchards fruit bins infested with overwintering codling moth have been a significant source of invading moths. Our research (Lacey et al., 2005b) demonstrates that EPNs can also provide effective and affordable control of codling moth larvae in fruit bins prior to returning them to orchards. CONCLUSIONS Entomopathogenic nematodes can provide control of overwintering codling moth when temperatures are 15˚C (60˚F) and higher and moisture is maintained. In trellised apples and conventional pears this moisture was adequately maintained by pre and post wetting trees using existing irrigation. Mulches offer promise to extend the persistence and activity of nematode larvicidal activity. Further research on optimizing the use of mulches in conjunction with entomopathogenic nematodes will be the subject of future research at the Yakima Laboratory. Figure 2. Mortality in cocooned codling moth sentinel larvae after application of two million Steinernema feltiae or S. carpocapsae infective juveniles per tree using an airblast sprayer or lance applicator.