Cercospora spp. cause foliar disease and form leaf spots on the leaves of a wide variety plants. Symptoms on the leaves vary by host but the leaf spots often enlarge, coalesce, and cause early senescence. Gray leaf spot (GLS), caused by Cercospora spp. is a significant disease of corn in the United States. Currently, there are two known species of Cercospora that cause GLS of corn, C. zeae-maydis (previously Group I C. zeae-maydis) and C. zeina (previously Group II C. zeae-maydis). GLS of corn is the most destructive disease compared to other corn diseases in the United States and Ontario, Canada causing the greatest yield loss. Aside from cultivar resistance, fungicides are often used for disease management. Therefore, this thesis focuses on establishing fungicide sensitivity of Cercospora spp. of corn.In Chapter 1, I provide background and literature review of Cercospora spp. that are infecting corn and cultural practices used to mitigate losses to GLS. In my second chapter I validate fungicide movement in corn plants via several fungicide applications that contain flutriafol as active ingredient during planting and assess disease suppression by the fungicide. This is to show that this fungicide is effective in protecting the plants from planting until harvesting. Next, in Chapter 3 I conducted a multistate survey across 17 states within the United States and Ontario, Canada to identify Cercospora spp. associated with and pathogenic on corn, as well as conducted fungicide sensitivity testing on these isolates. This study established the fungicide sensitivity of flutriafol on corn plants. Finally, in Chapter 4 I present conclusions and impacts of the studies. Overall, the studies in this thesis provide information about a new fungicide that can be used to control GLS and Cercospora spp. that were infecting corn.
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