Hello Kate,

Thank you for entrusting your lawn care questions to us.

Fungus diseases in lawns are difficult to positively diagnose without lab tests. Multiple experts can look at the same pictures and diagnose different fungus infections From the pictures you sent, I am pretty sure it is brown patch disease. Patch disease is a fungal disease that grows rapidly in hot, humid weather.

Once the humidity and temperature are favorable, the fungus spores that have overwintered in the soil infect the grass plants and spread rapidly. The conditions since mid-June have been perfect for the growth of lawn fungus disease.

Brown patch disease is caused by a fungus and generally affects the grass blades and the tillers (spreading mechanisms) but does not damage the crown of the grass plant. Once the conditions for fungus growth are no longer optimal, the grass plants will regrow, but the affected area is left thin and sparse.

Here is a good article about patch diseases. Homeowner action is summarized at the end of the article. https://www.extension.purdue.edu/extmedia/bp/bp-106-w.pdf

There are general cultural care recommendations that can limit the damage of a fungal infection. You can try adding a light dose of nitrogen fertilizer. Also, when watering, make sure you water early in the day so that the grass blades are dry by dark. Some fungus attacks when the grass is stressed, and some added nutrition can help fend off the pathogen. Fungicides are generally the defense against fungal infections, but there are limitations with them as well: Fungicide effectiveness is fungus strain dependent. By the time you see the damage it is essentially too late to treat with a fungicide. The damage has occurred in the weeks to a month preceding. Even when the appropriate fungicide is applied at the appropriate time, they are not 100% effective.

My thought is that the patterns you shared are consistent with Fungal Patch Disease. But the only way to confirm that is lab testing. Take a sample at a margin so that you have the dead grass, the dying margin and good grass all in the sample. Send this sample to the MSU Diagnostic lab to have the type of grass and the type of fungus identified. The services and cost structure for MSU Diagnostic Services can be found at: https://www.canr.msu.edu/pestid/

Tips on how to take a good sample can be found at: https://www.canr.msu.edu/pestid/submit-samples/

The results from the lab will positively identify the fungus, so you know what fungicides you should apply and when they should be applied. It will also identify the type of grass, because maybe you can grow a different cultivar that is less susceptible to your type of fungus.

Once you get your results from the MSU Diagnostic Lab, feel free to answer with the results, so that we can suggest a treatment plan.