Seeing Spots: Leaf Spots on Cool Season Turfgrass Angela Orshinsky Assistant Professor and Extension Specialist Department of Plant Pathology University of Minnesota
“Leaf spot” is one of the most common turf diseases that I have come across since arriving in Minnesota two years ago. However, leaf spot is a very vague description for such a diverse array of pathogens and diseases. In this article, I’d like to go over what leaf spots I have been seeing, their identification, when they tend to appear, and what strategies you can use to prevent their appearance and manage them when they do show up. What’s out there? Through site visits and samples that have been submitted to the University of Minnesota Plant Disease Clinic (pdc.umn.edu), I have found Bipolaris sorokiniana, Drechslera erythrospila, D. poae, Marielliottia triseptica, Leptosphaerulina trifolii, Curvularia spp. and Nigrospora sphaerica. Some of these pathogens look a great deal alike, especially Bipolaris spp. and Drechslera spp. Conidia from both species can have three to twelve septa (cross walls), are darkly pigmented, and form at the end of dark conidiophores on the leaf surface. At one time, both fungi belonged to the same genus - Helminthosporium. However, it was later discovered that they have different sexual
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