1a. Objectives (from AD-416):
The objective of this program is to identify and implement an integrated management non-fumigant methodology to control soilborne pathogens and weeds in strawberry production systems. The effects of anaerobic soil disinfestation, mustard seed meal amendments and organic acid material alone or in combination on fruit yield, soilborne disease and weed control will be determined. The contribution from this unit will focus assessing efficacy of these treatments, determining the role of soil biology in any observed disease control, and identifying the functional biological elements that have a role in disease suppression.
1b. Approach (from AD-416):
The capacity of different control strategies and integrated methods for suppression strawberry root infection will be determined in large field assays and in greenhouse assays. Greenhouse trials will focus on the biological ramifications of such control methods on soil biology, the temporal nature of these changes, and the effect of these changes on disease control. Based upon the findings from these experiments field trials may be modified and integration strategies altered to enhance control efficacy.
3. Progress Report:
This project relates to objective 1 of the associated in-house project, which seeks to determine the relative contribution of chemistry and soil biology to the control of soilborne plant diseases that is realized though soil incorporation of various organic material including brassicaceae seed meals. Experiments were conducted to assess the effect of application sequence on integration of anaerobic soil disinfestation (ASD) and mustard seed meal (MM) applications for disease control in a natural field soil from Santa Maria, California. Brassica juncea seed meal and rice bran-based ASD treatments were applied individually or in combination. Treatment sequences consisted of ASD/MM and MM/ASD, with a two or three week interval between treatment applications. Additional treatments consisted of a no treatment control, MM or ASD alone, and a co-application of MM+ASD at the same time. Sequence of application significantly influenced the effect of MM+ASD treatments on soil pH and growth of strawberry in Santa Maria field soil. Initial soil pH was 7.9 in the un-treated control and ranged from 7.6 to 8.06 in soils that received MM alone or MM after ASD treatment. In contrast, pH ranged from 6.2 to 6.4 in soils that received ASD alone or last in the application sequence. Plant growth was significantly improved in response to all ASD or MM treatments relative to the control. However, when MM was applied to the soil two or three weeks after Rice bran-ASD treatment, strawberry growth was significantly improved relative to the individual treatments or when ASD followed MM application. Rice bran-ASD alone, with MM, or when applied in the treatment sequence MM/Rice bran-ASD produced a bacterial community that was distinct from that realized in response to MM alone or the treatment sequence Rice bran-ASD/MM. The cause for reduced efficacy of the MM/ASD sequence relative to ASD/MM treatment is not known. Multiple factors could contribute to the response including reduced generation of fungicidal and nematicidal compounds produced in response to MM amendment or the elevated generation and retention of phytotoxic compounds. Extended aerobic incubation periods after application of the ASD process may alleviate the latter possibility.