Lawn Diseases - Fusarium Blight
Fusarium blight first appears as small, circular, grayish green areas, ranging from a few inches up to a foot in diameter. Some plants in the center of the circles may survive, giving them a frog eye or donut appearance. The crow or base area of the dead stems is affected with a reddish rot and is hard and tough. At times, a pink layer of the fungus can be seen near the soil line. The dead foliage appears bleached The fungus survives as mycelia in plant debris and plants killed by previous infections, or as thick walled resting spores (chlamydospores) in the thatch and soil.
The fungi that cause fusarium blight survive the winter in the thatch layer and on infected grass roots, crowns and rhizomes. As temperatures increase above 70° spore production begins. When air temperatures are between 75° and 90° and humidity is high spore production becomes profuse and affected grass may die in 4 to 7 days after the first symptoms appear. The fungi show little activity when air temperatures are below 70°, or when humidity is very low.
Fusarium blight occurs most commonly in areas that have been stressed for moisture and in areas in full sun. Follow proper irrigation and fertilization practices and regularly dethatch the turfgrass. Fungicides may be required if the turfgrass has a history of fusarium blight, but complete control is difficult to achieve with fungicides.