Answer: A Glyphosphate such as Roundup is your first weapon to kill out zoysia. You need to make sure the zoysia is growing juicy and lush and green, before spraying. Very critical when trying to kill any of the warm climate grasses, to make sure they are actively growing or else the plant will not absorb much of the Glyphosphate. Most people think that since they are trying to kill the grass, so watering and feeding it is the last thing comes to their minds.
But, if the zoysia is stressed for water and fertilizer or it is too early in the year so it is not growing much, the spray is a waste of money and time as the grass plants will not absorb the spray while they are semi- or fully dormant. And, even with all this, it is still most likely they will need to spray two or more times to get full kill.
Spray once and leave the grass alone for a week or two to allow full absorption and transfer to the roots of the poison. Then rake and mow off the dead grass, and immediately water well and deeply to see if any is left alive to regrow. Repeat as necessary. Once any remaining stems green up and are lush again, spray again on those
patches and repeat the wait period. This is usually enough to wipe out any persistent warm climate grass.
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