Integrated Disease Management of Stemphylium Leaf Blight of Onion: Incorporating Host and Fungicide Resistance

Lead Applicant: Mary Ruth McDonald

Research Priority: Plant Health & Protection

Program Type: Tier 1

Funding Cycle: 2026/2027

Research Centre: Ontario Crops Research Centre - Bradford

Research Summary: Stemphylium leaf blight remains the main foliar disease affecting onion production in Ontario. The pathogen has developed resistance to many registered fungicides, limiting effective disease control. Building on previous research, this project will use new technologies to monitor fungicide resistance, evaluate new fungicides, and improve disease forecasting. A rapid molecular testing method will be used to assess fungicide resistance in current pathogen populations, helping growers avoid applying ineffective products. The project will also evaluate both new site-specific fungicides and older broad-spectrum fungicides, while updating disease forecasting models. In addition, a new and efficient screening method will be used to identify onion cultivars with greater resistance to the disease. Findings will support improved integrated pest management programs for onion production.