Optimization & Implementation of Biologically Active Soil Amendments As a Fumigation Alternative for Soil-Borne Disease Control in CA Strawberries
Physiology and Pathology of Tree Fruits Research
Project Number: 2094-21220-001-12
Specific Cooperative Agreement
Start Date: Sep 01, 2014
End Date: Aug 31, 2018
The California strawberry production system has historically relied on soil fumigation as a means to effectively manage a diversity of soil borne diseases which are the primary impediment to economic viability. The phaseout of methyl bromide and increasing restrictions on other fumigants due to health and environmental concerns make development of effective non-fumigant based disease control options critical for the economic survival of CA strawberry producers. Anaerobic soil disinfestation (ASD) techniques and mustard seed meal (MSM) amendments have demonstrated capacity to suppress many soil borne pests across a diversity of cropping systems and locations. In a series of controlled environment and field-based trials established in CA, ASD and MSM applications achieved strawberry yields that were comparable to pre-plant soil fumigation at multiple sites across production districts. However, notable exceptions were observed at certain sites where specific pathogens, such as Fusarium oxysporum f.sp. fragariae, were not effectively suppressed by ASD resulting in crop failure. Despite this limitation, the demonstrated efficacy of ASD has led to adoption of this method as a viable disease control practice, primarily by organic strawberry growers, and was used to treat nearly 500 acres in 2013. Implementation of ASD and MSM for soil-borne disease control in conventional CA strawberry production systems will require greater consistency and efficacy in order to replace soil fumigation as the primary control option. The goal is to make these methods a practical and economical option in CA strawberry production that can be readily incorporated into the existing systems, and that effectively manages plant pathogens and plant-parasitic nematodes across a wide range of environmental conditions. To achieve the goal of predictable and effective disease control through grower application of ASD and MSM, we will 1) examine environmental and biological variables that modulate disease control efficacy, 2) modify the ASD and MSM application protocol based on these findings to optimize disease control efficacy, 3) institute a series of demonstration trials in each of the three main production districts to demonstrate ASD efficacy relative to soil fumigation, 4) perform economic analysis of the optimized ASD system and compare to current fumigation strategies, and 5) develop extension materials, outreach programs and other resources to enhance grower adoption of ASD as an effective soil-borne disease control option.
A range of different C-sources including rice bran, wheat bran, and molasses, were previoulsy shown to be equally effective at reducing Verticillium wilt of strawberry. However, subsequent studies documented differential ASD pathogen suppression and disease control efficacy occurring in a carbon source input-dependent manner, which correlated with the spectrum of fungicidal/nematicidal volatiles produced and resulting soil microbial community profile. These differences were of specific note with regard to suppression of Fusarium wilt in strawberry. Soil temperature also affects suppression in a pathogen specific manner. Therefore, the effect of C-source, temperature, and soil type on the efficacy of ASD and MSM, and integration of these two methods, will be evaluated in a series of replicated field trials. C-sources and rates to be evaluated are based upon our previous field trials and include MSM (Brassica juncea/Sinapis alba formulation at 2 and 3 t/ac) rice bran (4.5 and 9 t/ac), molasses 6 and 9 t/ac, rice bran 4.5 t/ac + molasses 4.5 t/ac, wheat residue (7.5 or 15 t/ac), grape pomace (9t/ac), MSM+rice bran ASD, methyl bromide (or alternative fumigant) and non-treated control. Water availability can be a limiting factor under current CA drought conditions, and in a preliminary trial ASD efficacy was observed without soil saturation, but not in another field trial with limited water addition. Therefore, ASD trials will be conducted with and without standard pre-plant water at the time of C-source input to determine necessity of soil saturation for disease control efficacy. It is evident that soil-borne disease suppression in response to ASD involves the activity of resident soil biology and effective ASD has been associated with shifts in soil microbial community structure. Therefore, to identify potential functional groups, microbial community analyses will be conducted on soils collected post-treatment using Terminal Restriction Fragment Length Polymorphism and pyrosequencing-based (metagenome) analyses of bacterial 16S rRNA genes and the fungal internal transcribed spacer region. Treatment efficacy will be assessed based upon yield and disease suppression. N loss through leaching is a primary concern associated with ASD. Therefore, ASD with different types and rate of carbon sources, and thus N input levels, will be evaluated in these demonstration and replicated research trials. Soil inorganic N will be monitored monthly and plant N uptake every 2-3 months throughout the growth season. Soil inorganic N content will be measured using 2M KCl extractions and an auto analyzer.