Why is my lawn turning brown?

This lawn turned brown and dead-looking very quickly, but still has a healthy root system. Susan Rose, one of the turf experts at Colorado State University Extension on Orchard Mesa, determined that the culprit was Aschochyta leaf blight, which looks awful but usually goes away over time. Local conditions have created the perfect storm for the conditions to develop.

When faced with brown and dead-looking grass in the yard, it can be tempting to simply water more often. After all, it’s been hot and windy, and those two conditions can make a lawn dry out. While that may be true, it’s also true that hot and windy conditions can cause a turf condition known as Aschochyta leaf blight, which makes grass turn brown and look dead.

Aschochyta is a fungus, but it’s one that burns blades of grass from the top, leaving the grass completely rooted, with living, healthy roots.

“People see this and want to overwater,” said Susan Rose with Colorado State University Extension, “which can lead to a fungus disease that attacks the roots.”

Usually, the symptoms of Aschochyta show up very quickly, sometimes even overnight. The good news is the condition usually rights itself. Because turf is healthy at the roots, new growth will be green and will eventually replace the diseased portion of the leaf, which will get mown over time.

To reduce the occurrence of aschochyta blight, homeowners should aerate lawns, in either the summer or the fall. Frequent mowing is thought to contribute to the condition, so homeowners should avoid excessive nitrogen fertilizer in the spring, which would cause grass to grow quickly and need more frequent mowing.

Drought stress and irregular watering can also contribute to the development of ascochyta, so homeowners should check sprinkler systems and heads to make sure they are working properly and aren’t blocked by something else in the landscape. It may be necessary to stand in the spot where the brown spot is to make sure that the sprinklers that are supposed to reach it are, indeed, reaching it.

For the healthiest turf, lawns should be watered between midnight and 6 a.m. That may be difficult if you have manual controls for your irrigation system and would prefer to spend those hours sleeping rather than watering the lawn. Homeowners with a timed system should use it and water in the early morning hours. Homeowners with a manual system should try to water before 10 a.m. Watering in the early evening, between 6 and 10 p.m. can extend the period of time that a leaf is wet, which makes it more susceptible to fungal disease.

Ascochyta can be difficult to treat with fungicide, and since it usually goes away without causing any real damage to the turf, there’s no need to treat it.

Because other fungal diseases like necrotic ring spot are often caused or exacerbated by overwatering,  if you have what looks like a dead, dry spot in your lawn, don’t drown it in an attempt to make it go away.

If you have persistent brown spots that don’t go away with time in spite of good aeration, good irrigation and appropriate fertilization, cut a large sample out of the turf and bring it to the experts at Colorado State University Extension at the Mesa County Fairgrounds. They will probably be able to tell you what could be causing the discoloration and what you can do to treat it.


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