I don't have the answer but I'm sorry that happened to you. You sure it's not grubs or something of the sort?

 

Not grubs as I had put down an insecticide and preventative in the recent past.

 

I'd definitely check anyway, as that looks dramatic to be heat alone. Makes me think either insect damage or fungal. Or someone accidentally sprayed your yard with round up.
As for already applying insecticide, I know my armyworms were not phased by the first three products I tried, and several studies have found resistance in them to various products. Worth doing the soapy water test (1 tablespoon of dish soap mixed in a gallon of water- pour over an area on the border between good and bad and wait several minutes, watching to see if anything comes up) and also digging up an area - again on the border- and look for grubs under the turf. Also, close up photo of the blades in the border area would help show if there was a fungus.

 

I'm also thinking either insect or fungus. Zoysia will go dormant if not watered during heat, but you should have had that covered based on your post. I would try the soapy water test to see what bugs surface, and inspect/photo the blades near the area for possible fungal lesions. Nematodes are another possibility.

 

Pics of blades in and around immediate area? Perhaps fungus or insect damage as noted, try above tests.

 

@Greendoc has spoken about this in the past - nematodes. My understanding is nematodes are a big issue in Florida with Zoysia lawns so you'll want to take a look at that if at all possible.

 

Thanks guys. I'll take a look at blades where die-off and healthy blades are and post a photo. Nematodes - have heard plenty about them in Florida.....how do you kill them??

 

I had another area on other side of driveway about half this size react the same way and seemed most apparent during hottest part of day...

 

Chinch bug? I have similar damage right now bc of it

 

That looks like insect damage.

 

Pics near edge of die off and healthy areas @ktgrok @Spammage @ThomasPI

 

I'm not expert but I don't see any fungus. I'd be pulling up some sod to look for grubs, I think.

 

Insect and disease damage. Frequently performed operation for me is a combination broad spectrum fungicide. Imidacloprid if it has not been applied yet and Dylox. This is is all in one spray.

 

@up2parr24 I agree with Greendoc. I don't see much that says fungus, but there are some small lesions visible on some of the green shoots. There are several additional rolled leaves, which is zoysias way of telling you it's thirsty. Check with a screwdriver to see how easy it is to penetrate the soil as you could have a few areas that aren't allowing the water into the soil. A little shampoo sprayed at 2 oz per 1000 sf can help if that is the problem. The dylox is your best bet for a quick kill of many insects, and the imidacloprid is a systemic for a longer residual effect.

 

@Spammage @Greendoc thank you, fellas