Expert Knowledge Elicitation: Accessing the Big Data in Experts' Brains.

A vast amount of expert knowledge currently remains inaccessible to digital information systems. Expert knowledge elicitation is a systematic approach to accessing and synthesizing the insights of subject matter experts, especially when available objective data are incomplete. In plant pathology, expert knowledge elicitation is valuable for addressing urgent, uncertain, and/or future challenges, such as emerging disease threats, complex epidemiological systems, knowledge gaps when resources are limited, and future scenarios. This perspective explores when expert knowledge elicitation is most effective for addressing plant health challenges, emphasizing its role in informing timely, expert-based decisions. We discuss lessons learned from real-world implementations across diverse regions and pathosystems, highlighting strategies for eliciting, structuring, and interpreting expert-derived data, as well as associated caveats. We frame expert knowledge as a form of big data, and outline (i) how existing big-data streams (e.g., remote sensing, crowdsourced reports, and digital surveillance) can inform expert judgements; and (ii) how outputs from expert knowledge elicitation can be captured as scalable datasets (text, tabular, audio, and video) that enable AI-supported synthesis. We illustrate how expert knowledge can be integrated in Bayesian analyses, providing a transparent and rigorous approach to understanding uncertainty and improving inference. Finally, we outline future opportunities, including integration with artificial intelligence, to scale and strengthen expert knowledge elicitation in support of global plant health.