Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2013
Publication Date: 11/4/2013
Citation: Shennan, C., Muramoto, J., Baird, G., Koike, S., Bolda, M., Mazzola, M. 2013. Optimizing anaerobic soil disinfestation for soilborne disease control. Proceedings of International Research Conference on Methyl Bromide Alternatives. 13.1-13.4. 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) was developed in Japan and the Netherlands as an alternative to soil fumigation and involves the generation of an anaerobic environment through a combination of flooding and addition of a carbon source to the soil system. Disease control is believed to result from the production certain volatiles that are generated by microorganisms that are active under anaerobic conditions. Anaerobic soil disinfestation has been consistently effective in the control of Verticillium wilt of strawberry when rice bran was used as the carbon input. However, the rates of rice bran required are high (9 ton per acre) and come with potential hazards due to the high nitrogen inputs, and therefore potential loss, associated with this input. Therefore, anaerobic soil disinfestation was conducted using a range of carbon inputs and rates in field trials conducted at multiple sites in California. Lower rice bran rates (6 ton per acre) or rice bran (4.5 ton per acre) plus molasses (4.5 ton per acre) as the carbon input used in ASD was as effective as the high rate of rice bran in controlling disease and increasing strawberry yields. The ASD treatments that included rice bran as a carbon source provided yields that were equivalent to pre-plant fumigation at multiple sites. However, at one site where Fusarium wilt was a significant yield limiting factor, disease control was not attained. At this site, although ASD suppressed Fusarium wilt progression and increased yields relative to the control, all plants were dead by the end of the growing season. In future trials, application methods will be modified to optimize ASD for the control of Fusarium wilt.
Technical Abstract: Soilborne disease management without chemical fumigants is a major challenge for strawberry production in California. Current re-registrations and regulations are likely to intensify this obstacle by severely limiting availability of fumigants on a large percentage of strawberry acreage. Anaerobic soil disinfestation conducted using rice bran as the carbon input has provided effective control of multiple strawberry soil-borne diseases including Verticillium wilt in field evaluations. However, for reasons of both cost and potential leaching of nitrogen from soil systems, ASD using lower rice bran application rates or different carbon inputs were evaluated in multiple strawberry field trials. In three field trials (one conventional, two organic), marketable fruit yields in response to anaerobic soil disinfestation applied with rice bran at the standard rate (9ton per acre), at a reduced rate (6 ton per acre) or in combination with molasses (4.5 ton per acre) resulted in marketable fruit yields that were significantly greater than the control. ASD conducted using molasses as the sole carbon input did not significantly increase fruit yields. At the one conventional site that possessed a fumigation control, yields attained in ASD treatments that contained rice bran as a component of the carbon source input performed as well or were superior to pre-plant PicChlor or methyl bromide soil fumigation. At one site, although yields were significantly enhanced relative to the control, severe incidence of wilt, caused by Fusarium oxysporum, was observed later in the growing season and all plants were dead by trials end. This finding indicates that a modification of the ASD system as previously applied will be necessary to control this important pathogen of strawberry. Distinctive fungal communities were established in response to fumigation and ASD with rice bran treatments but it is interesting to note that the communities in the ASD molasses treatments were unchanged relative to the no treatment control. This shows that carbon input itself, rather than the period of anaerobic conditions, is key to the development of distinctive microbial communities that may contribute to ASD-induced disease suppression.