Field scale application of Brassica seed meal and anaerobic soil disinfestation for the control of apple replant disease

Apple replant disease caused by a complex of soil-borne fungi, oomycetes, and nematodes causes stunting and reduced yields when apples are planted in locations previously cropped to tree fruit. Anaerobic soil disinfestation and bio-renovation using mustard seed meals have successfully mitigated replant disease in greenhouse trials and small field plots. The objective of this study was to examine the efficacy of Brassica seed meal and anaerobic soil disinfestation for the control of replant disease at a commercial scale in apples. At three 0.4 to 5 ha field sites in Washington, United States anaerobic soil disinfestation and Brassica seed meal bio-renovation were compared to non-treated and fumigation with 1,3-dichloropropene/chloropicrin controls. Brassica seed meal treatments significantly altered composition of the bulk soil and rhizosphere microbiomes and resulted in apple tree growth as great or greater than fumigated controls across all three study locations. Anaerobic soil disinfestation resulted in significant changes to composition of the rhizosphere microbiome and tree growth that was greater than the no-treatment control in three of four experiments. Our findings indicate that both methods may serve as biologically effective alternatives to soil fumigation for control of apple replant disease, though further modifications may be required to ensure their economic feasibility.