Online

Brown, Anna Rissland

Plant and Soil Science

2023

M.S.

Rhizoctonia solani Kühn is an aggressive saprophytic soilborne fungal plant pathogen that is distributed globally and infects many crops including Solanaceae, Fabaceae, and Asteraceae. The lack of effective organic methods to control R. solani and the resulting yield losses contribute to the economic insecurity of farms and farmers. The overall aim of this study was to compare two organic certifiable approaches to manage bottom rot caused by R. solani (subspecies AG1-IB) in field-grown organic lettuce: anaerobic soil infestation (ASD) and thermophilic compost cured by vermicompost (vermicompost). A commercially available biocontrol product and an untreated control were used as references. Two concurrent, adjacent experiments were conducted at two commercial organic farms for two consecutive growing seasons in 2020 and 2021. Vermicompost and the biocontrol product RootShield® PLUS+G were incorporated separately into seeding starter media, sown with lettuce seeds, and 3-week plants were transplanted into unamended field soils. ASD treatments were implemented in situ on the farms and included an examination of four different soil amendments widely available and commonly used by local growers. Disease incidence, disease severity, and percent marketable yields were used to assess treatment success. Supplemental laboratory and greenhouse studies were conducted to confirm or refute the trends observed in the field. A farmer survey was conducted to quantify the economics of each practice and the likelihood of adoption. This study demonstrated that the ASD method is achievable in a field setting on Vermont vegetable farms but did not create disease suppression to compensate for the cost of materials and labor to establish. Vermicompost was less expensive and more effective than RootShield® PLUS+G. Neither ASD nor vermicompost were more profitable than standard growing practices. However, vermicompost is likely to be adopted by farmers in part because of the ease of treatment implementation and added soil health benefits. The findings of this study inform farmer's best management practices and contribute to the body of research seeking effective tools to manage soilborne pathogens in commercial organic agriculture.