2013 Annual Report
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.
This serves as a final report for project 5350-22000-019-02R which expired 1/31/2013. 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. The effect of soil treatments, including anaerobic soil disinfestation (ASD) and mustard seed meal amendments, on microbial community dynamics, disease suppression and plant growth, was assessed in California strawberry production systems. At two field trials, treatment-specific effects on fungal and bacterial community composition were detected based on examination of microbial community similarity from individual field plots using terminal restriction fragment length polymorphism (T-RFLP) data. Prior to treatment applications there was a general randomness in the relative similarity of the fungal community among plots, with no clustering of treatments. However, post-application, all plots for a particular treatment possessed highly similar fungal community composition and grouped together based upon the Shannon Diversity Index. At both sites, all treatments with ASD as a component were clustered and at MBA this was also observed for all treatments possessing a mustard meal component. Similar trends were observed with regard to treatment effects on bacterial community composition; however the effects were less definitive.
Overall, ASD was shown to be consistently effective at suppressing Verticillium dahliae in coastal California when 20 Mg ha-1 of rice bran was pre-plant incorporated and at least 75 mm of irrigation was applied to sandy-loam to clay-loam soils. In trials at Watsonville, Castroville, and Santa Maria, marketable yields from ASD plots were generally equal to or higher than Pic-Clor 60 plots, and significantly greater than untreated controls. In the 2012-2013 season, some California berry growers started to implement ASD at commercial scale; ~20 growers used ASD in 32 fields (mostly organic) ranging from 0.2 to 8 ha in size, totaling 50 ha. As of early June 2013, most growers who implemented rice bran-based ASD appeared to be satisfied with plant performance and yield level especially those possessing fields with high disease pressure, planning expansion of ASD treated fields. However, applying 20 Mg ha-1 of rice bran for ASD, which provides ~400 kg ha-1 of total N, can release excess nitrogen to the environment, thus there is need to examine whether lower rice bran rates or alternative carbon sources can yield effective disease control.