It is ok to "mulch" regularly mowed zoysia if the mowing is done with a front throw reel set to cut at 11/2" or less. A reel chops up clippings pretty fine. The mowers designed for St Augustine and cool season grasses cannot be expected to mow zoysia. Thankfully, I mostly see rotary mowers on St Augustine and weed areas.
When the zoysia has been mowed incorrectly, even a reel will have problems cutting it down. I use either a Landscape Blade counter rotating cutter or else a carbide tipped saw blade brush cutter. A reel mower is to do the final clean up after the grass has been cut down to below 1".
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