Ascochyta symptoms may develop throughout the growing season but are more common during hot, droughty periods that were preceded by cool, rainy conditions.

Large irregular patches of turf rapidly turn a straw-color and appear dead. Often times Ascochyta is mistaken for burns or fertilizer striping since it can follow mower tracks – leaving lines of damaged grass in a lawn. From a distance, the yard may appear to have a silvery sheen since it is only the tips of the blades being affected. Although the dieback within an area appears complete from a distance, healthy leaves are often intermingled within the patch.

Ascochyta is usually restricted to the leaves; bluegrass crowns and roots typically are not killed. Leaves infected with Ascochyta often exhibit a tip dieback that extends about a third to halfway down the leaf blade. The margin between healthy and diseased tissue is abrupt and slightly pinched. In addition there is often a dark band between the green portion of the grass blade and the blighted tip.

The disease normally hits in the late spring and summer. It is closely tied to moisture changes, especially drought stress caused by watering restrictions or 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. Frequent mowing and dull mower blades may contribute to disease severity by creating more infection sites (wounds).

MANAGEMENT:

Ascochyta can be managed by following good lawn care practices to minimize stress in the lawn.

• Maintain grass height between 2½ and 3 inches. Minimize excess damage of the leaf blades by maintaining sharp mower blades.
• Mow when the yard is dry. Avoid mowing during wet weather, especially when Ascochyta is active.
• Ascochyta tends to follow mower tracks; washing the under carriage of the mower after mowing and cutting infected areas last can help. Bagging the clippings and removing them also takes infected material away from the lawn.
• Try to maintain even soil moisture. Check the irrigation system to make sure all sprinkler heads are working properly and insure water is being distributed evenly to avoid drought stress. Extra watering of Ascochyta infected areas is the best way to help grass outgrow the disease.
• Turf usually recovers completely after a couple of weeks with extra water being applied to damaged areas. Watering deeply less often is far better than more frequent shallow watering. Keep in mind humidity levels are normally very low in Colorado, so the first several minutes of watering often does not get a chance to get into the soil.

Although several fungicides will inhibit Ascochyta growth, they can be expensive and difficult to apply. Furthermore Ascochyta leaf blight development is sporadic and rapid, making timing of preventive fungicide applications all but impossible.