Hi, Chris from Kean Landscaping & Design. Without inspecting it, sounds like brown spot. Make sure your mowing at 2”-2.5” and catch the clippings. Zoysia doesn’t like to be cut high. It’s a little late but treat with a fungicide, either granular (water in) or liquid. You can’t cure brown spot but you can treat it. If you pull the deadish grass, it releases easily and is blackish at the base, its brown spot.
Any questions call or email,
Keanlandscaping@yahoo.com
727-593-0253