Rotation length, crop rotation, anaerobic soil disinfestation and mustard seed meal affect organic strawberry yield and soil-borne disease incidence in California
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.
Zavatta, M., Muramoto, J., Mazzola, M. and 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 Hortic. 1309, 501-508
non-fumigant alternatives, Fusarium oxysporum f. sp. fragariae, Macrophomina phaseolina, Verticillium dahliae