Grey leaf spot (GLS) is a foliar fungal disease that affects maize, also known as corn. GLS is considered one of the most significant yield-limiting diseases of corn worldwide. There are two fungal pathogens that cause GLS: Cercospora zeae-maydis and Cercospora zeina. Symptoms seen on corn include leaf lesions, discoloration (chlorosis), and foliar blight. Distinct symptoms of GLS are rectangular, brown to gray necrotic lesions that run parallel to the leaf, spanning the spaces between the secondary leaf veins. The fungus survives in the debris of topsoil and infects healthy crops via asexual spores called conidia. Environmental conditions that best suit infection and growth include moist, humid, and warm climates. Poor airflow, low sunlight, overcrowding, improper soil nutrient and irrigation management, and poor soil drainage can all contribute to the propagation of the disease. Management techniques include crop resistance, crop rotation, residue management, use of fungicides, and weed control. The purpose of disease management is to prevent the amount of secondary disease cycles as well as to protect leaf area from damage prior to grain formation. Corn grey leaf spot is an important disease of corn production in the United States, economically significant throughout the Midwest and Mid-Atlantic regions. However, it is also prevalent in Africa, Central America, China, Europe, India, Mexico, the Philippines, northern South America, and Southeast Asia. The teleomorph (sexual phase) of Cercospora zeae-maydis is assumed to be Mycosphaerella sp. Host and symptoms Corn is the only species that can be affected by Cercospora zeae-maydis. There are two populations of Cercospora zeae-maydis, distinguished by molecular analysis, growth rate, geographic distribution, and cercosporin toxin production. Cercospora zeae-maydis differs from its cousin group Cercospora zeina sp. nov. in that it has a faster growth rate in artificial media, the ability to produce the toxin cercosporin, longer conidiophores, and broadly fusiform conidia. Cercospora zeina sp. nov. affects corn in the Eastern Corn Belt and Mid-Atlantic States; Cercospora zeae-maydis is found in most corn producing areas of western Kentucky, Illinois, Indiana, Iowa, Wisconsin, Missouri, Ohio, and west Tennessee (Midwest). Both populations share the same symptoms and virulence, the ability of the fungus to invade the host. Major outbreaks of grey leaf spot occur whenever favorable weather conditions are present (see below). The initial symptoms of grey leaf spot emerge as small, dark, moist spots that are encircled by a thin, yellow radiance (lesions formation). The tissue within the “spot" begins to