Southern Blight & Turf

Southern Blight

• Southern blight fungal spores live in the thatch layer between grass blades and soil. When thatch builds up to more than 1/2 inch, grass is at risk of contracting the disease. Humid, warm weather is another environmental factor favoring Southern blight's germination. This fungal disease thrives when temperatures are between 85 to 95 degrees but becomes active at 75 degrees, according to the University of California. Monitor lawns for signs of the disease when the weather is hot.

Damage

• Southern blight causes reddish-brown rings in the yard. These rings are as large as 9 feet in diameter, according to the University of California. Closely examine discolored grass blades. Look for light- or dark-brown bumps, called sclerotia, on the grass blades' base. Sclerotia resemble mustard seeds, according to the University of California. The grass within the ring may look healthy and green.

Cultural Treatment

• Check your thatch layer. A thick thatch layer harbors Southern blight fungal spores and blocks fungicides. Cut a 2-inch, wedge-shaped piece of turf out of the lawn and measure the thatch. Before removing thatch, mow the lawn to 1-1/2 to 2 inches high so the power dethatcher blades can pull out the thatch. Push a power dethatcher back and forth across the lawn. Rake up the debris.

Chemical Treatment

• Apply a fungicide containing azoxystrobin, triadimefon or flutolanil, as suggested by the University of California. Apply the fungicide over the yard. Avoid applying fungicide to lawns that are water stressed or when temperatures exceed 90 degrees, as it can injure grass. Reapply the fungicide according to its directions. The timing depends on the amount of rain and the severity of damage.