Use of a summer cover crop as a partial carbon source for anaerobic soil disinfestation in coastal California

Authors: MURAMOTO, J - University Of California; SHENNAN, C - University Of California; Mazzola, Mark; WOOD, T - University Of California; MIETHKE, E - University Of California; RESULTAY, E - University Of California; ZAVATTA, M - University Of California; KOIKE, S - University Of California - Cooperative Extension Service

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2019
Publication Date: 2/27/2020
Citation: Muramoto, J., Shennan, C., Mazzola, M., Wood, T., Miethke, E., Resultay, E., Zavatta, M., Koike, S.T. 2020. Use of a summer cover crop as a partial carbon source for anaerobic soil disinfestation in coastal California. Acta Horticulturae. 1270:37-44. https://doi.org/10.17660/ActaHortic.2020.1270.4.
DOI: https://doi.org/10.17660/ActaHortic.2020.1270.4

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. However, the need for suitable carbon material inputs can be a cost-limiting impediment to the use of this disease management strategy. The current study was conducted to assess the effectiveness of different cover crops cultivated on site for use as a carbon input for ASD with or without supplemental rice bran input. Among the six cover crops evaluated (broccoli, mustard, Florida rye, Italian rye, Sudan grass, triticale) mustard, Florida rye and triticale provided maximum biomass, which ranged from 6-7 t per hectare. Total biomass was supplemented with rice bran to attain a total biomass input of 20 t ha-1. Additional ASD treatments include rice bran alone, weed only biomass, and a no carbon input control. When conducted in summer, effect ASD soil conditions were obtained with anaerobic conditions developing and a soil temperature of 31 C obtained. Suppression of Fusarium oxysporum f. sp. fragariae, causal agent of Fusarium wilt, soil populations was observed under these experimental conditions for all ASD treatments. When ASD trials were conducted in autumn under lower temperature environment, effect control of Verticillium wilt, caused by Verticillium dahliae, was achieved. These studies demonstrate that summer cover crops can be an effective partial ASD carbon source for the control of Fusarium oxysporum f. sp. fragariae and V. dahliae, which may result in a reduced cost for application of this treatment.

Technical Abstract: Anaerobic soil disinfestation (ASD) and mustard seed meal (MSM) appear to be promising non-fumigant alternatives for soilborne disease control. A series of ASD experiments were conducted using a summer cover crop as a partial carbon source in coastal California (CA) with the goal of reducing ASD’s external inputs. A randomized complete block-designed field trial with 6 cover crop plots (open-pollinated broccoli, mustard, FL104 rye, Italian rye, Sudan grass, triticale) plus no cover crop plots (weeds only) and rice bran 20 t ha-1 plots was conducted to control Fusarium oxysporum f. sp. fragariae (F.o.f) in Watsonville, CA. Cover crops were grown from May to July 2017. The highest biomass was obtained for triticale, FL104 rye, and mustard (6-7 dry biomass t ha-1) while the remaining cover crops did not produce sufficient biomass due to the moderate air temperature (average 14 °C) typical in the area. Cover crops were mowed and incorporated with rice bran added at a rate to provide a total of 20 t ha-1. A flat ASD treatment with clear totally impermeable film (TIF) was conducted from July to August 2017. Strong anaerobic conditions developed during ASD treatment in all plots, and soil temperature under the clear TIF at 20 cm depth averaged 31 °C despite average air temperatures as low as 15 °C. Findings indicated that this approach significantly reduced F.o.f. inoculum density regardless of the cover crop type when the summer ASD treatment period was extended for 5 weeks or longer. A pot trial using the same experimental design yielded effective suppression of Verticillium dahliae in naturally infested soil with a 3-week autumn ASD treatment at a lower soil temperature condition. Together, the present study demonstrated that summer cover crops can be an effective partial ASD carbon source for the control of F.o.f. and V. dahliae.