Large Patch in Zoysia

Q: I have zoysiagrass. It was beautiful last summer…thick and green. I feel that the lawn maintenance people we have mowing our lawn did not keep the lawn cut low enough. It always seemed too high.

They just started cutting it down a level last week and now this “black” is showing through. Can you help ?

A: I think there is a good chance you have a disease called zoysia large patch. It begins growth in the fall, sometimes where zoysiagrass is mowed too high and accumulates a thatch layer. The black streaks are caused by organisms that are decomposing the dead grass stems.

Dark streaks seen in zoysiagrass in spring are common.

There are five steps for control of large patch:

1. Apply a fungicide like Immunox or Bayleton or Scott’s Lawn Fungus Control every September and October (27 days apart) and every May

2. Fertilize only after May 1

3. Control moisture – do not irrigate unless the soil is dry and then only 1 inch per week in one application

4. Mow at 1 1/2 inches every week

5. Aerate the zoysiagrass thoroughly in May and rake the resulting dirt plugs into the grass. This will innoculate the thatch with fungi, which will help reduce the thatch layer.

6. Generally speaking, fungicide application in spring is not helpful. Maximize your work toward fertilizing and mowing properly.

Zoysiagrass Care Calendar

Large Patch (UGA)

Large Patch (Kansas State)


Large Patch (North Carolina)

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