Detection of resistance in <i>Phytophthora infestans</i> to the carboxylic acid amide ( <scp>CAA</scp> ) fungicides using digital droplet <scp>PCR</scp>

The assay developed will allow for the accurate and sensitive detection of CAA resistance conferred by alterations at amino acid position 1105 in the CesA3 gene in P. infestans. The capacity to use the assay with multiple DNA sources and potential to adapt the 'drop-off' approach to different ddPCR platforms will ensure its applicability to the wider P. infestans community in monitoring the continued use of CAA-based fungicides for P. infestans management. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.