Fusarium Blight

• Two fungal disease agents, Fusarium roseum and F. tricinctum, are responsible for this pervasive lawn diseases. According to the North Dakota State University Extension, fusarium blight is actually a conglomeration of three separate diseases -- necrotic ring spot, rhizoctonia yellow patch and summer patch. Symptoms of fusarium blight include distinct "frog eye" patterns of crescent-shaped areas of dead grass with an area in the center of healthy, green grass.
  
  

Rhizoctonia Blight

• Formerly known as brown patch, this lawn disease is caused by the fungus Rhizoctonia solani. Patches of infected grass will first take on a dark green, water-soaked appearance. These patches will later dry out and turn tan, brown, purple or black. These patches are called "smoke rings" and are often the most conspicuous symptoms of a lawn that has been infected with rhizoctonia blight.
  
  

Typhula Blight

• Typhula blight is another common lawn blight disease. Caused by the fungi Typhula incarnata and T. ishikariensis, the earliest symptoms of this disease are straw-colored patches that grow in size. Hard fungal fruiting bodies called sclerotia appear on the lawn as the disease progresses. This disease is sometimes called gray snow mold, and snow molds describe a whole group of lawn blight diseases that tend to infect lawns immediately after snowfall.
  
  

Pythium Blight

• Pythium blight, on the other hand, favors hot, humid weather. The fungal agent of this common lawn disease is Pythium spp. Intermittent spots break out over the lawn that, in the early mornings, have a water-soaked appearance as well as a greasy or slimy texture to the touch. In the later stages of infection, the spots will turn tan and brown as the grass dies.