Evaluation of bactericides and plant defense inducers in the presence and absence of onion pathogens Pantoea spp. and Burkholderia gladioli in Colorado

2022 Summer.Includes bibliographical references.Bacterial diseases can cause significant annual crop losses if left untreated. U.S. onion growers combat bacterial disease pressure through a variety of management practices, including crop rotation, irrigation management, and proper cold storage postharvest. In 2019, twelve national research institutions formed a collaborative project called "Stop the Rot" (StR) to develop diagnostic identification tools and research cultural practices across different onion growing regions to mitigate onion bacterial rots. As part of that effort, CSU researchers conducted two years of field trials in 2020 and 2021 to compare the efficacy of commercially available bactericides to prevent bacterial rot on three different onion cultivars (Avalon, Snowball, Vaquero). Artificial bacterial inoculation was prepared using Pantoea spp. and Burkholderia gladioli isolates. The pesticide products included the following types: traditional copper bactericides (Kocide and ManKocide), sanitizers (Oxidate 5.0), biological microorganisms (BlightBan A506), and plant defense inducing productions (Actigard and Lifegard). At harvest in year one, the incidence of bacterial rot was not significantly impacted by bactericide treatment since rot was not present in 2020. In 2021, for 'Vaquero' onion, the Kocide treatment had significantly more rot compared to other treatments and the control after cold storage. For 'Snowball', the BlightBanA506 treatment had a significantly- higher rot percentage than the ManKocide treatment. These results will help Colorado onion growers accurately assess production risks and select bactericides that meet their needs on the farm. Ongoing research on bactericide efficacy, combined with collaborative results from colleagues in Georgia, New York, Utah, and Washington, will help domestic producers "stop the rot" in their onion crops