Here is the picture that tells the story. See the reddish color in the roundish shape with the fringe of yellowing grass around it. That is classic fungal disease.

{{gwi:90246}}

It is long past time to stop watering 2-3x per week and start letting the surface of the soil dry out. How long are you watering each time (rhetorical question)? Take that number, double it, and water that long all at once. Then watch the grass to see when it starts to wilt or lose its luster. When that happens, hopefully in more than 3 days. If it goes a full week, then water that same length of time the next time. If it does not go a full week, then water deeper (longer) the next time. You should adjust the time the water stays on so that the soil surface dries out completely before watering again, but the grass does not wilt. That means deeper watering so the roots will grow deeper and they can take advantage of that deeper moisture.

There are two approaches to resolving fungal issues. What has become the classical approach is to get the exact nature of the disease diagnosed and use the exact chemical on it that is supposed to work. You have to apply the chemical under the right conditions of temperature, humidity, soil dry/wetness, while taking future temps, humidity, and dry/wetness into account. In San Antonio the only day of the year when I could apply chemical fungicide would be January 14th because we get heat, humidity, or rain the rest of the year.

The second approach is to try one of the organic approaches. With an organic approach you have to have a little more faith because they take 3 full weeks to show improvement. Sometimes (and I have never had this happen) they do not work at all and your grass is 3 weeks deader. The classic organic approach is to apply ordinary ground corn meal (yes, like you cook with) at a rate of 20 pounds per 1,000 square feet over the entire lawn. The way it works is as the corn decomposes on the soil, it attracts a fungus which kills other fungi to live. Several of the fungi it kills are the classic lawn diseases of Sclerotinia minor (root rot), Sclerotium rolfsii ({{gwi:90245}}) and Rhizoctonia (brown patch). Note that you do not need a careful diagnosis to use corn meal. It seems to cover many diseases. Being an organic fertilizer, corn meal is going to be beneficial no matter what happens. At a relatively low dose of 20 pounds per 1,000, you cannot do any damage. Again, it takes 3 full weeks to see the improvement.

Two diseases that do not seem to be controlled by corn meal are rust and red thread. Those seem to be controlled by milk sprayed at 2-3 ounces per 1,000 square feet.

By the way, disease is one of the very negative factors in zoysia grasses. Once it gets a disease and spots die out, it can take some zoysias a long time to recover and fill back in.

Where do you live and why did you pick Zorro?

You also look to have a thatch problem.

Thanks dchall for your advises. I live in Austin and I have several big live oaks in the backyard so I chose the grass which is supposed to be shade tolerant and better disease resistant than St Augustine. I mush have watered the lawn too much by 5-7 minutes/zone every time using a rotating sprinkler. After I noticed the problem, I have applied Spectracide Ready-to-Spray Lawn Disease Control Systemic Fungicide a couple of weeks ago. I'll give it a try the corn meal this weekend.

Some following up question if you have a clue please jump in.

Is the disease called "brown patch"? The lawn was started from sod a few month ago but only greens up recently. The root system is not established yet. When should I mow it for the first time? should I address the thatch problem later when the lawn is more established?

>"but only greens up recently"

Well, that's zoysia! The last grass on the planet to green up in spring.
By July, it will be fully green.

And you do not have thatch - that's just dormant Zoysia.

>"The root system is not established yet"

Because you were only watering for 5 to 7 minutes.

When watering fresh sod, you must soak it so that the water gets PAST the sod and soaks the soil beneath, This forces the roots to seek the moisture in the depths of the soil and take root hold. Whoever sold or installed the sod surely told you this I would assume.

After some research I think my lawn has "brown patches". "Active infections are noticeable by yellow leaves at the edges of patches. Leaf sheaths become rotted, and a gentle tug on the leaf blade easily separates the leaf from the runner.The root seams not affected.

Since the lawn is not established yet. I am wondering if removing the affected sods and replacing with healthier ones is a better way at this point to control the progression of the disease.

Do you guys think it will be helpful or is it worth doing that?

I think the lawn have "brown patches".

Before I put down sod, I actually removed the rocks in the yard (there were many of them), laid 3-4 inch soil and installed the sprinkler system during last winter. The reason we rushed to put down sod is the we were losing soil because of rain. We would like to have a lawn where my kids can play and run around. The frond yard is some kind of st Augustine doing well in sun but not shade. The backyard is moderately shady. Some online source says that Zorro Zoysia is resistant to many fungus disease including the "brown patch" but it looks like it isn't bullet proof. I definitely watered too often and too shallow because of the fear of grass drying out. During the winter months, all the yard is yellowish.

My next plan is to buy 1/2 pellet of same grass and replace the patches showing symptoms. Apply corn meal. I also plan to save the affected patches and lay them in a separate location and watch them. These a couple of days, the growth of the whole law is fast. the lawn looks much greener than a couple of weeks ago.

My hope is that since Zorro might be more resistant to the diseases and by corn meal/compost and proper watering, I may still save the lawn.

With my 2nd baby coming in June, I have to put everything together fast. If you guys are interested I will keep updating the progress.

Been researching Zorro Zoysia and would love to get your thoughts & some pics about it once you get the problem under control. Good luck.