Breaking the brown bridge for residue-borne fungal disease control in broadacre agricultural systems. A review

Crop residues, plant material remaining post-harvest, provide critical ecosystem services, including reducing erosion, conserving soil moisture, and building soil organic matter. Globally, a “residue revolution” is underway, with substantial increases in the quantity and persistence of residues driven by the expansion and intensification of annual crop production systems, widespread adoption of conservation agriculture principles, and growing recognition of the system benefits gained through residue retention. However, crop residues also act as reservoirs for damaging fungal crop pathogens, allowing them to persist between seasons and initiate residue-borne disease epidemics via inoculum carryover. Current management relies heavily on in-season management via genetic resistance and chemical controls, rather than preventative strategies that address off-season inoculum carryover. Consequently, broadacre production systems are increasingly vulnerable, as pathogens adapt to overcome genetic and chemical controls, partly due to the large populations persisting on residues. Despite this growing risk, previous review articles have overwhelmingly focused on individual pathogens or in-season management, with limited examination of the universalities of residue-borne diseases with respect to off-season survival and reproduction on residues. Here, we review an interdisciplinary body of research to address this gap. We (i) summarize key aspects of residue-borne pathogen biology, including reproduction, survival, and dispersal; (ii) outline global trends in agriculture collectively driving residue-borne disease risk; (iii) evaluate current and emerging management strategies that target residue-borne pathogen inoculum using an integrated disease management pyramid, with emphasis on breaking the “brown bridge” of off-season inoculum carryover; (iv) highlight key social and economic barriers to the adoption and integration of these management strategies; and (v) outline future research and investment priorities for the development of sustainable, systems-integrated solutions. This review provides growers, agronomists, and researchers with a framework for managing crop residues to reduce residue-borne disease risk while preserving the agronomic and ecological benefits of crop residue retention.