Hello Rob

The cause could be brown patch - Rhizoctonia Brown Patch at this link: https://archive.lib.msu.edu/DMC/Ag.%20Ext.%202007-Chelsie/PDF/e1537-1981.pdf

You might want to send a sample to MSU Plant and Pest Diagnostics Lab. But first you will have to send images.

So please follow these directions:

Click on this link: https://www.canr.msu.edu/pestid/

PLEASE READ - Important notice to all our clients

Then click on the box that says: How to submit a sample

PLEASE READ

- Important notice to all our clients

- Plant Health Analyses

- Crop Specific Details

Residential Turf

Include a square of turf from the margin of the diseased area so that both healthy and diseased turf is included. Minimally, the turf square should be 6 inches x 6 inches. An intact layer of soil should remain on the root system. Wrap samples in newspaper and pack in a box for shipment. Do not add moisture to the turf prior to shipment. Provide a detailed description of cultural practices (irrigation, fertilization, pesticide application, etc.) and images of the symptoms in the lawn with the sample.

Ship/Deliver Samples Directly at:

MSU Plant & Pest Diagnostics

578 Wilson Road, CIPS 107

East Lansing, MI 48824

If this condition is under trees you may what to consider shady lawn alternatives - Check out the below articles:

Will grass grow in my shady lawn? - At this link: https://www.canr.msu.edu/news/will_grass_grow_in_my_shady_lawn

Shady lawn alternatives - At this link: https://www.canr.msu.edu/news/shady_lawn_alternatives

PDF file at: https://www.canr.msu.edu/uploads/files/Shady_lawn_alternatives.pdf

Hope this helps!!

You are welcome - Have a great day!!