Augmenting predators for pest control in apples

Authors: Schmidt, Rebecca; Moretti, Erica; Rehfield-Ray, Linda

Submitted to: Western Orchard Pest and Disease Management Conference
Publication Type: Abstract Only
Publication Acceptance Date: 11/29/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic apple growers in Washington state are testing releases of predatory insects purchased from commercial suppliers. This method is more environmentally-friendly than pesticides. There is almost no information on best practices for releasing predators in tree fruit. Current recommendations are based primarily on work in greenhouses or in low-growing crops like strawberries. These environments are very different from outdoor production in tree fruit; pest species and climate are different, so different predators, release methods, or number released may be appropriate. Researchers at the USDA-ARS in Wapato, WA tested releases of mealybug destroyers for control of mealybug and lacewings for control of aphids. In 2020, both early (mid-May) and late (mid-June) timing and high (5,000/acre) and low (2,000/acre) rates of mealybug destroyer releases decreased mealybug counts. Release by drone did not appear to be effective, possibly because the mealybug destroyers were attracted to light and flew upwards instead of landing in the trees. When a drone release at dusk was tested in 2021, it did not lower mealybug counts, but pest levels were very low in the plots that year, so further testing is needed. Eggs of Chrysoperla carnea and larvae of C. rufilabris lacewings both reduced aphid counts by 50%. The “C. carnea” larvae delivered were the incorrect species (C. externa instead), which may have caused the lack of success with that treatment. These results and future work will allow growers to improve efficacy of predator insects for pest control, resulting in decreased use of pesticides and higher yields.

Technical Abstract: Organic apple growers in Washington are experimenting with releasing natural enemies purchased from commercial insectaries. Unfortunately, release recommendations are typically based on greenhouse use, in crops with small canopies, and in environments with higher humidity and lower temperatures than in central Washington. In 2020-2021, we tested two rates, timings, and methods (drone versus ground) of release of mealybug destroyers for control of grape mealybug in organic apple. In 2021, we also tested two species (Chrysoperla rufilabris versus C. carnea) and life stages (eggs versus larvae) of lacewings for control of aphids. In 2020, mealybug destroyers released on the ground reduced mealybug populations, although between-plot variation was high and the differences were not statistically significant. The mealybug destroyers were highly dispersive and difficult to find within plots. Drone releases were not successful, likely because mealybug destroyers did not land in the plots due to attraction to sunlight. The 2021 attempt of the trial, which included a drone release at dusk, did not find differences between treatments, likely because mealybug populations were too low to sustain the predators. Releases of C. carnea eggs and C. rufilabris larvae reduced aphid populations by 50% compared to the control, but the other two treatments did not. The shipment of C. carnea larvae was found to contain C. externa instead, which may be responsible for the poor efficacy of this treatment. These results and future work will be used to create scientifically-based recommendations for releasing natural enemies in orchards