Effects of crop rotation, anaerobic soil disinfestation, and mustard seed meal on disease severity and organic strawberry production in California

Authors: SHENNAN, C - University Of California; MURAMOTO, J - University Of California; BAIRD, G - University Of California; ZAVATTA, M - University Of California; NOBUA, B - University Of California; Mazzola, Mark

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2019
Publication Date: 2/27/2020
Citation: Shennan, C., Muramoto, J., Baird, G., Zavatta, M., Nobua, B., Mazzola, M. 2020. Effects of crop rotation, anaerobic soil disinfestation, and mustard seed meal on disease severity and organic strawberry production in California. Acta Horticulturae. 1270:63-70. https://doi.org/10.17660/ActaHortic.2020.1270.7.
DOI: https://doi.org/10.17660/ActaHortic.2020.1270.7

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) and mustard seed meal (MSM) amendments have demonstrated the ability to control certain soil-borne diseases in California strawberry production systems. The current study was conducted to assess the effectiveness of ASD or MSM when integrated with crop rotation practices as a means to control soil-borne diseases in strawberry. This study demonstrates that crop rotation with broccoli prior to growing strawberries, and use of ASD can effectively control Verticillium wilt caused by Verticillium dahliae in the strawberry crop. The combination of a short (2yr) rotation with lettuce as the rotation crop significantly increased disease incidence and resulted in low yields, but this was partially mitigated by use of ASD. If lettuce, a V. dahliae host, is grown before strawberry for economic reasons then it is important to use ASD to reduce disease levels in organic strawberry production.

Technical Abstract: Anaerobic soil disinfestation (ASD) and mustard seed meal (MSM) appear to be promising non-fumigant alternatives for soilborne disease control. Studies were conducted to compare two and four-year organic crop rotations, with either lettuce or broccoli as the main rotation crop between strawberries, in conjunction with MSM or ASD. Strawberries were planted every other year in rotation with lettuce (let 2yr) or broccoli (br 2yr), and every fourth year in rotation with broccoli–lettuce/cauliflower–broccoli (br 4 yr) or lettuce-broccoli-lettuce (let 4yr). Each rotation included four fertility/disease management approaches: 1) bare winter fallow + strawberry with fertigation (bf); 2) winter legume/cereal cover crop before vegetables and anaerobic soil disinfestation (ASD) prior to strawberry planting and fertigation (cc); 3) same as for cc except with supplemental compost added annually, and organic fertilizer added as needed to vegetable crops based on pre-sidedress nitrate tests (cc+c+f); and 4) same as cc except a cereal rye cover crop was used and mustard seed meal added as an amendment at cover crop incorporation and prior to strawberry planting (msm). Strawberry yields and wilt severity were monitored for each crop, and in year 6 pathogen levels in strawberry crowns were assessed using real-time qPCR. In all three years when strawberries were grown, yields were negatively related to severity of wilt symptoms, and in year 4 (all rotations) and year 6 (2yr) yields were higher in the br than the let rotations. In year 4 a positive effect of ASD was found in 2yr but not 4yr rotation treatments, and in year 6 highest yields were in the ASD treatments. The primary pathogen present was Verticillium dahliae, which was significantly reduced by the br rotations and ASD. In year 6 crown infection with V. dahliae was lower in br than let 2yr rotations. Rotation with broccoli and ASD show promise for reducing V. dahliae in organic strawberry production.