Supplemental data for: Improving tools for management of Stemphylium leaf blight of onion in Ontario: Overwintering of Stemphylium vesicarium in alternative weed hosts

The overwintering sources of S. vesicarium inoculum that initiate SLB epidemics each season are not fully understood. This study investigated whether S. vesicarium could survive on inoculated weed hosts under natural overwintering conditions in the Holland Marsh, and examined how tissue decomposition varied among weed species over winter.

The experiment was conducted over two consecutive overwintering seasons: Trial 1 (2021-2022): Eight weed species inoculated and exposed to outdoor winter conditions at the Ontario Crops Research Centre, Bradford, ON, returning to the greenhouse in March 2022. Trial 2 (2022-2023): Ten weed species assessed with increased replication. Plants were spray-inoculated at 2 x 10^5 conidia/mL and assessed for S. vesicarium conidia detection and residue decomposition upon return to the greenhouse.