Why is My Lawn Yellow After Rain? | Why is My Lawn Yellow After Mowing? | How to Fix Yellow Lawns

If your lawn turns yellow following a rainstorm or after mowing, the grass is probably struggling with a common lawn fungus called ascochyta. In this video, our lawn specialist explains how to identify and correctly manage ascochyta.

This lawn disease hides in the thatch layer and flares up when rain splashes it onto the grass blades. Ascochyta also spreads easily through lawnmower blades. Luckily, it only affects the tips of the grass blades and usually dissipates within a few weeks of a flare-up.

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Transcript:
Are you seeing splotchy, brown areas in your lawn that just seem to appear overnight? Your grass might have a fungus called ascochyta leaf blight. Ascochyta can often be mistaken for a possible fertilizer burn by how quickly it can appear after a fertilizer treatment has been done. It can also look like drought stress when the temperatures are extremely hot, but you can tell the difference between drought stress and ascochyta by checking the grass blades.

While drought stress affects the entire grass blade, ascochyta causes the blade to pinch about a third of the way down, which causes the upper portion to turn yellow while the grass underneath usually remains unaffected. As a result, ascochyta usually only shows on the lawn for about 2-3 weeks before fading, but that can also depend on the weather. This disease is often difficult to control or kill with a fungicide, so most people simply wait for it to grow out after a few weeks.

The fungus lives in the thatch layer of the lawn year-round and affects the grass when it’s disturbed by rain and the temperatures are right. Because of this, Utah homeowners generally see ascochyta appear on their grass when hot, dry weather is immediately followed by cool, rainy conditions. So, to help alleviate the effects of the disease, here are a few suggestions.

First, as we mentioned, the fungus is in the thatch layer, so aerating your lawn yearly will help remove the fungus. We suggest that the machine is properly cleaned before using to make sure that this and other diseases won’t spread throughout the lawn.

Next, keep your lawn properly watered and mowed to prevent damage from ascochyta during these weather conditions. Damage to the grass blade creates a wound where the fungus can easily enter into the blade, so you should also mow less frequently when you see the disease to avoid spreading it and only mow when the lawn is dry. Also, keep your lawn around 2.5-3 inches long. Thanks for watching! Call or text our office for information about our lawn care services.