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

Abstract

Abstract Codling moth (CM), a serious pest of apple and pear in most countries where these fruits are grown, overwinters in cryptic habitats as cocooned diapausing larvae. Control of diapausing CM larvae would reduce or eliminate damage to fruit early in the following growing season. Entomopathogenic nematodes (EPNs) have shown promise as biological control agents of cocooned CM larvae in the Pacific Northwest and elsewhere, but several factors, such as choice of EPN species and other operational factors warrant investigation to provide growers with practical control options. 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). 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. 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.