Supplemental data for: Improving tools for management of Stemphylium leaf blight of onion in Ontario: Disease forecasting trials

Field trials were conducted in 2021 and 2022 at the Ontario Crops Research Centre in Bradford, Ontario (Holland Marsh) to evaluate disease forecasting programs for their ability to reduce fungicide applications while maintaining effective disease management. Trials were arranged in a randomized complete block design with four replicates using yellow onion cv.

Traverse, a variety susceptible to SLB. Forecasting programs were compared against a calendar-based spray program and untreated controls (with and without EverGol penflufen seed treatment). Disease severity was assessed throughout the growing season and at final destructive harvest on 16 August in both years.