Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: November 6, 2011
Publication Date: November 14, 2011
Citation: Mazzola, M. 2011. Advances in Brassica seed meal formulation for apple replant disease control. In: Proceedings Annual International Conference on Methyl Bromide Alternatives and Emissions Reductions, 11/9/2011, Fresno, California. 6.1-6.4. Interpretive Summary: Organic soil amendments often have been promoted as a means to control soilborne plant diseases. However, the consistently effective use of such an environmentally sensitive method of disease control requires attention to details of the implementation process. While individual Brassicaceae seed meals are not an effective treatment for the control of apple replant disease, multiple seed meal formulations were found to be as effective as pre-plant soil fumigation. Seed meal formulations were as effective as fumigation in controlling parasitic nematodes and fungal pathogens, and improving apple tree growth when planted on three organic orchard sites previously planted with apple. However, plant growth was affected by the season of application and the apple rootstock that was utilized. On sandy soils, significant phytotoxicity and tree death was realized when seed meal application was made during the spring of planting, but this response was eliminated if seed meal application was made in the autumn prior to planting. Tree death was not observed when the same seed meal formulations were applied in the spring of planting on sites containing a finer soil texture with high organic matter content (3-4%). Although all seed meal treatments were effective in improving tree performance to the level obtained through soil fumigation, the response appeared to be greater when used in concert with the rootstock Geneva 11 relative to the rootstock M9. Optimum levels of disease control required the use of a virtually impermeable film to cover treated soils for a minimum period of two weeks following seed meal application. The results indicated that pre-plant application of Brassicaceae seed meal formulations can be an effective measure for control of replant disease, but that certain site-specific factors must be considered, including application date and rootstock, to achieve optimal tree performance.
Technical Abstract: Brassicaceae seed meals when used independently do not provide uniform and sufficient control of the pathogen complex that incites apple replant disease for this soil amendment to be used as a viable alternative to pre-plant soil fumigation. Therefore, field trials were established at multiple sites to evaluate the efficacy of seed meal mixtures which were formulated based upon the known activity of different seed meal components towards the individual biological elements that incite this disease. Trials included multiple seed meal formulations, application dates and apple rootstock sequences. When seed meal amendments were applied approximately one month prior to planting and tarped with a virtually impermeable film, a Brassica juncea/Sinapis alba seed meal formulation significantly improved apple tree growth at two (STM and Tukey) of the three orchard sites and suppressed the target pathogen complex at all field locations. At the third orchard site (SR), application of this same seed meal formulation resulted in significant phytotoxicity and approximately 40% tree death, but the degree of tree morality was rootstock-dependent. A B. juncea/Brassica napus seed meal formulation was as effective as the B. juncea/S. alba amendment when utilized with the G11 rootstock and did not incite significant phytotoxicity. Application of the seed meal formulation in the autumn prior to planting at SR orchard resulted in tree growth that was equivalent to that attained in response to pre-plant soil fumigation. The B. juncea/S. alba seed meal formulation reduced in-row weed coverage by approximately 85% at the STM orchard and weed suppression was evident at the end of the growing season. These data indicate that the seed meal formulation may be as or more effective than Telone-C17 fumigation for control of replant disease, but that plant back periods and seasonal application requirements will vary with soil type.