Rotation length, crop rotation, anaerobic soil disinfestation and mustard seed meal affect organic strawberry yield and soil-borne disease incidence in California

Authors: ZAVATTA, MARGHERITA - University Of California Santa Cruz; MURAMOTO, JOJI - University Of California Santa Cruz; Mazzola, Mark; SHENNAN, CAROL - University Of California Santa Cruz

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 2/12/2021
Publication Date: 4/19/2021
Citation: Zavatta, M., Muramoto, J., Mazzola, M., Shennan, C. 2021. Rotation length, crop rotation, anaerobic soil disinfestation and mustard seed meal affect organic strawberry yield and soil-borne disease incidence in California. Acta Horticulturae. 1309(72):501-508. https://doi.org/10.17660/ActaHortic.2021.1309.72.
DOI: https://doi.org/10.17660/ActaHortic.2021.1309.72

Interpretive Summary: Soil-borne disease management without chemical fumigants remains a major challenge for strawberry production in California, and modifications to existing regulations are likely to intensify this challenge by further limiting availability of fumigants on a large percentage of strawberry acreage. Anaerobic soil disinfestation (ASD) has demonstrated the ability to control certain soil-borne diseases in California strawberry production systems. Modifications to the ASD application method or integration with other management tactics will be necessary to effectively control the multiple lethal soil-borne diseases, including Verticillium wilt, Fusarium wilt and Macrophomina crown rot, that jeopardize California strawberry production. ASD or mustard seed meal soil amendment (MSM)were applied in concert with a 2-year or 4-year crop rotation system with lettuce or broccoli grown in the year immediately prior to planting strawberry. All three soil-borne diseases were detected at the study site, but the dominant disease had changed from Verticillium wilt in the first 6 years to be dominated by Verticillium and Fusarium wilt by year 8 (2019). In year 8, ASD conducted using rice bran as the carbon source, in the 4-year rotations, provided the highest strawberry yields. When used in concert with lettuce rotations, yields in ASD plots was superior to that attained with MSM. The combination of broccoli rotation and MSM produced strawberry yields equivalent to ASD. Over all rotations, ASD treatment yields were higher than the MSM treatment. While the rotation/ASD treatments did not completely eliminate all three diseases monitored in this study, the treatment provided sufficient disease suppression to greatly enhance strawberry yields under this very challenging disease environment.

Technical Abstract: Soil-borne diseases represent a major threat for organic strawberry growers. Fall application of anaerobic soil disinfestation (ASD) can control Verticillium dahliae and reduce severity of Macrophomina phaseolina, whereas control of Fusarium oxysporum f. sp. fragariae (Fof) requires summer ASD application. In an 8-year replicated trial we tested the effect of crop rotation in combination with ASD or mustard seed meal (MSM) to assess disease suppression and yield performance. We compared strawberry grown every 2 versus 4 years, with broccoli or lettuce grown before strawberry. Four treatments were established within each rotation: 1) cereal/legume winter cover crop plus compost and fertilizer + ASD before strawberry; 2) cereal winter cover crop and MSM 3.7 t ha-1; 3) cereal/legume winter cover crop + ASD before strawberry; 4) bare winter fallow (bf) + strawberry fertigation. We report on year 8 of the trial (2019) when all plots were planted to strawberries. Both V. dahliae and Fof were detected in soil in year 6, therefore ASD was applied in summer 2018 using rice bran + broccoli or lettuce residues as carbon sources. Strawberry yields were highest when ASD was used in 4 year rotations. ASD notably improved yields in the lettuce rotation, whereas MSM yields were higher in broccoli compared to lettuce rotations. Both ASD treatment yields were significantly higher than MSM and bf when averaged across all rotations. The 2-year rotations showed higher strawberry wilt symptoms, and a negative correlation between wilt score and yield was found (R2=0.37, p<0.0001). Analysis of crown tissues show Fof, M. phaseolina and V. dahliae were all present in the field. While ASD did not eliminate disease, it provided sufficient disease suppression to greatly enhance strawberry yields. The combination of broccoli rotation and MSM produced strawberry yields equivalent to ASD, but MSM was not effective in lettuce rotations.