I read what you wrote, but it still looks like it is being overwatered.

Monthly chemicals??? If you had bermuda, then, yes to monthly fertilizer; but you have zoysia. Seasonal fertilizer should be plenty. What else is in their chemical brew? Insecticide??? Herbicide??? Fungicide??? None of those should be used unless you have a diagnosis of weeds, insects, or disease. NONE.

Given where you are, I would first check with the applicators to see what they have already put down. If they are putting down anything in addition to liquid fertilizer, then I would discontinue their service. The problem is those extra poisons kill the beneficial microbes living in the soil. The result is unhealthy soil and, possibly, what you are seeing. In order to recover from this, I would put down 15 to 20 pounds per 1,000 square feet of any organic fertilizer. Give it 3 weeks to work. You'll be skeptical that it's doing anything at 2 weeks, so 3 weeks is needed. Here is a picture of a zoysia lawn fertilized with a handful of alfalfa pellets.

Thanks to mrmumbles for posting that picture in this forum 12 years ago. Organic fertilizers work.

If you have more questions, please reply with the addition of your location.

One more thing...you should put the mulch away from the trunk of your tree to allow the trunk to breathe. Ideally the roots should be exposed at the base of the tree. Why? Tree trunk bark is susceptible to diseases when it is buried like that. Tree root bark is "designed" to withstand continual contact with the soil, but not the trunk.

I am interested in your use of "alfalfa pellets" as lawn food. So you simply spread some quantity of alfalfa pellets around your yard, whereupon, presumably, they decompose in situ and thus fertilize the soil? If so, I can do this.

YES, you have the idea. The application rate is 15 to 20 pounds per 1,000 square feet. There are a couple of things to know about buying them and the application. When I buy, I ask for rabbit chow. If you go to a feed store and ask for alfalfa pellets, they assume you are looking for horse cubes...at least in my part of Texas that's what they assume. Horse cubes are the size of your thumb while rabbit chow is more like 5/32-inch in diameter. Alfalfa is a supply and demand type of commodity, so prices will vary from location to location, season to season. It comes in 50-pound bags (20 kilo if you're buying in Canada).

As for applying, they do not go through any of my spreaders. I could rent a broadcast spreader that looks like it would work, but instead I put about 2 pounds into a 2-pound coffee can and spread them by hand. Take the can to the lawn and eyeball out a 10-ft by 10-ft space on the lawn. Two pounds per 100 square feet is the same as 20 per 1,000. Standing in one spot I toss the contents of the can onto the 100 square foot area. Then I replenish the can and continue on. It makes no difference whether you overlap or miss a little. Well, if you miss enough the grass will tell you and you can apply more in 3 weeks when you notice the issue. But you cannot overapply this stuff (unless you leave a heaping pile of it on the lawn). After you have the area covered, give the area a misting to moisten the alfalfa pellets. They don't go to work until they expand and work their way down to the soil. Misting will expand them. The day after you will see what I mean as the tiny little pellets will have bloated up into long 'worms' sitting proudly on the grass. Then I drag a hose across the grass to knock the expanded flakes down into the turf where they can get to work. Then set your calendar for 3 weeks. That's 21 days. It will seem like forever, but do not expect to see results before that time. The biological process of decomposing the alfalfa into plant food takes just that long. One more thing, during the first few days after you might sense the 'aroma' of decomposing alfalfa. If you ever lived on a farm you won't even notice, but some people do notice it and don't like it. Trust that the fragrance will disappear soon enough.

You can apply these types of organic fertilizer any time you want to, rain or shine, day or night, day after day, summer or winter (although the soil temp needs to be above 50F for the microbes to be awake). You can even apply the same day as you apply chemical fertilizers. Because the two work so completely differently, there is no interaction. My other favorite organic fertilizer is ordinary corn meal, yes, like you eat. Only I get mine from the feed store in 50-pound bags when I buy the alfalfa pellets.