Kentucky Bluegrass Lawns

ASCOCHYTA LEAF BLIGHT is a common disease of Kentucky Bluegrass lawns in Colorado. The disease results in rapid development of large, straw-colored blighted areas of the lawn during late spring – early summer. Blighting is usually restricted to the leaves – bluegrass crowns and roots typically are not killed. Leaves infected with the fungus often exhibit a bleached tip that extends approximately a third to halfway down the leaf blade.

The disease occurs in late spring and summer and appears to be enhanced by soil moisture fluctuations, especially drought stress caused by watering restrictions and poor irrigation system coverage. However, the disease may also develop during periods of hot weather preceded by unusually wet soil conditions caused by excessive rain or over-irrigation.

Ascochyta can be managed by following good cultural practices that minimize stress in the lawn.

• Reduce thatch and promote water penetration through the soil by yearly aeration. Maintain grass height between 2 ½ and 3 inches. Minimize wounding of the leaf blades by keeping mower blades sharp.
• Avoid mowing during wet weather, especially when Ascochyta blight is active. Reduce mowing frequency and increase mowing height during Ascochyta outbreaks.
• Maintain a balanced fertilization program.
• Try to maintain uniform soil moisture.

Remember that Ascochyta blight is primarily a foliage and not a root or crown disease. Therefore individual bluegrass plants are usually not killed. Given enough time, usually several weeks depending on the weather, new leaves will emerge from the surviving roots. Be patient following a disease outbreak and maintain normal management practices.