Relentless Gardener: Addressing late summer lawn issues

One of the more common problems is Ascochyta leaf blight. It is caused by the fungus Ascochyta spp. It affects Kentucky bluegrass and sometimes tall fescue and perennial ryegrass.

Hot, dry weather following periods of rain or irrigation can cause stress in the grass. The leaf tips are pinched, straw-colored, and die back. The lawn looks scorched no matter what you do. If you look closely at the leaf blade, you can see black fungal fruiting bodies.

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Water more consistently. Do not mow heat-stressed turf in the middle of the day. It is not recommended to use fungicides. Give the grass 6-8 weeks to recover depending on the amount and severity of the damage.

Other cultural practices include mowing no more than one-third of the leaf blade in one mowing. Aerate the lawn in the fall and spring to improve water infiltration and soil oxygenation. Do not apply excessive nitrogen, especially in the heat of summer. This turf needs more water, and fertilization can cause scorching. The grass is attempting to survive the heat. It will return to active growth when the weather cools. Understanding and working with your grass’ life cycle will help you keep it healthy. In this case, the crowns and roots are not infected.

Dollar spot is another lawn issue that starts as small, silver-dollar-sized, straw-colored spots that merge. This becomes most active when temperatures are 60-85 degrees Fahrenheit. It thrives when combined with high humidity, heavy dew, or wet leaves overnight, and low nitrogen fertility. Think of it this way: cool nights and warm days. Damp, cool mornings after a warm day. It is prevalent with Kentucky Bluegrass and tall fescue.

The best practice to control dollar spot is better cultural practices. Apply the proper amount of nitrogen. Mow properly and water deeply early in the morning. Aerate to reduce thatch. When necessary, use fungicide if it is out of control.

For more information, visit www.ext.colostate.edu.