Epidemiology and Management of Stemphylium Leaf Blight on Onion (Allium Cepa L.) in The Holland Marsh, Ontario
Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium Wallr (Simmons) (teleomorph: Pleospora allii. (Rabenh.) Ces. & De Not), is a destructive disease of onion. The objective of this study was to assess the epidemiology of SLB in Ontario and evaluate management strategies. Stemphylium leaf blight first appeared at the end of June to mid-July in 2015 and 2016, coinciding with air-borne conidia of S. vesicarium (based on spore trapping), frequent rainfall, and air temperatures ≥ 15 °C. Onion cultivars Pontiac, Milestone and Hendrix were slightly less susceptible to SLB compared to the other commercial cultivars in the study. A protective application of fluopyram plus pyrimethanil at the 3 4 leaf stage reduced SLB incidence, but later applications had little impact. Aerial infrared photography demonstrated the potential to identify differences in onion plots, but these differences were not related to SLB. Additional research is needed to evaluate more fungicides and spray-timings for SLB management.