Significant reduction of overwintering codling moth larvae would provide substantial protection to fruit early in the following growing season. Field trials of Steinernema carpocapsae and S. feltiae infective juveniles were conducted in apple and pear orchards under a variety of conditions to determine the effects of nematode species and seasonal temperature, adjuvants, post-application irrigation and method of application on efficacy. If moisture within the cryptic habitat in which codling moth cocoons are located is maintained for 8 hours and temperatures are above the threshold of activity for the nematodes species employed (10-15°C), up to 100% mortality of cocooned larvae in possible. Similar findings were observed in fruit bins infested with codling moth larvae that were treated with infective juveniles. Adjuvents that improve penetration of cryptic habitats and help to maintain moisture improved nematode activity against overwintering codling moth larvae.