Goal: To develop a sustainable management plan for Stemphylium leaf blight (SLB) of onion.Obj. 1: Fungicide evaluation and grower adoption.Annually monitor for developing field resistance to fungicidescurrently used for the control of SLB, and screen for efficacious fungicides in FRAC groups not currently used by the NY onion industry through on-farm small-plot fungicide evaluations and field scouting. Results will be conveyed to growers through weekly discussion groups during the onion-growing season at which time growers will be supplied with fungicide recommendations based on field assessments and outcomes of research objectives.Obj. 2. Disease prediction.Field-test disease predictive models based on environmental conditions as a tool for sustainedfungicide use for SLB.Obj. 3: Development of PCR techniques to detect fungicideresistance.Develop PCR techniques to detect mutations in the hexokinase(HK), cyp51 and succinate dehydrogenase genes in which mutations have been associated with resistance in other fungi to FRAC 2, 3 and 7 fungicides respectively , amplify DNA from isolates with known fungicide sensitivity phenotype and determine sequence differences associated with fungicideinsensitivity.Obj. 4: Monitoring of fungicide resistance.Quantify the incidence of mutations associated with fungicideinsensitivity in S. vesicarium collected from the four main onionproducing regions, to determine the extent of insensitivity, and shifts in sensitivity over time.