Tactics to improve natural enemy releases in tree fruit
Author: Rebecca Schmidt-Jeffris
Published: 2024
Summary: Growers have experimented with releases of natural enemies to control pests in organic apples, but there are currently no best practice recommendations for releases in orchards. The purpose of this project was to determine which natural enemies and release methods showed the most promise for controlling orchard pests. We also examined the potential of lures and supplementary food products for recruiting resident natural enemies and retaining released natural enemies. Releases of mealybug destroyers (2,000 or 5,000/acre) showed promised in a preliminary trial (2020), but in the three following trials (2021-2023), they did not lower mealybug counts and rapidly dispersed from the orchard. Because this insect costs $680-950/acre to release, the low chance of success means that fruit growers should avoid using this insect and other options should be explored for mealybug control. Lacewing releases varied in efficacy. In 2021, releases of C. plorabunda eggs (100,000/acre) or C. rufilabris larvae (20,000/acre) reduced aphid abundance by 57% and 43%, respectively. In the following two years, none of the lacewing release treatments reduced aphid abundance. We attributed this to very high initial aphid counts in 2022 and poor survival of released lacewings in 2023, potentially due to the use of organic pesticides. Across all years, releases of lacewing larvae resulted in higher recapture than releases of eggs. Low numbers of released lacewings were recovered in all trials, even in treatments where aphid abundance decreased. Therefore, when determining efficacy of beneficial releases, scouts should focus on pest numbers, not necessarily natural enemy recovery; however, presence or absence of the released natural enemy can give some sense of survival. Releases should be conducted earlier in the season than anticipated (mid-April in southern Washington) to get an adequate head-start on aphids. Multi-site studies are needed to fine tune recommendations, but early season (mid- to late April) releases appear to be critical for success. Tactics for retaining and recruiting natural enemies had highly variable results between sites and years. In general, methyl salicylate lures showed some promise for recruiting lacewings and Stethorus. Food supplements may have increased retention of released O. insidiosus and subsequently reduced thrips abundance. The use of lures after a lacewing release should be investigated to determine if they encourage released lacewings to remain in the orchard after they develop into adults. Key words: lacewing, mealybug destroyer, Orius insidiosus, lures, supplementary foods
