2019 ASHS Annual Conference

Sweet cherry (Prunus avium L.) is an important cash crop in the United States, where Washington is the principal producer. The value of the 2017 crop exceeded one billion dollars with 81% of production in the Pacific Northwest. A constant challenge for growers is unpredictable fruit set caused by inclement weather during early spring bloom and the disruption of pollination by climate change and colony collapse disorder. A more reliable method to pollinate commercial crops is needed to ensure yield security. Our team at Washington State University has been investigating an alternative pollination system of pollen suspensions applied with electrostatic sprayers. This work is investigating: 1) the potential for commercial artificial pollination and, 2) the variability in sweet cherry pollen performance. In 2018, we conducted field trials in commercial sweet cherry orchards across Washington to examine pollen application rates and timing. The following treatments were applied depending on location: no-spray control, suspension mix-only, 30 grams of pollen per acre by airblast application, and electrostatic applications of 15, 30, and 60 grams of pollen per acre. We collected and analyzed data for percent of flowers open at time of application, fruit set, and yield. To assess pollen performance among cultivars and growing seasons, we collected pollen from ten cultivars at the WSU-Roza research farm in 2017 and 2018 and used germination tests to determine viability. Across treatments in electrostatic field trials, mean fruit set (n = 351) ranged from 4% - 53%. Yield data from trials in Finley and Brewster suggested an increase in the pollen treated trees, but was not significant (P = 0.50, P = 0.36 respectively). No treatment effect was observed in the field trials. Our data suggest that application at earlier stages of flowering may have increased efficacy. These trials direct further research in which pollen viability is monitored throughout application. In pollen viability assays, there was variation among cultivars in 2017 (P = 0.0001) and 2018 (P = 0.001), as well as variation between growing seasons (P = 0.0001 – 0.40, depending on cultivar). Overall, this research suggests there is potential for electrostatic spray systems to ensure consistent, reliable pollination. Further investigation of cultivar variability, pollen viability, spray rates, and schedules is required to maximize the efficacy of such systems.