Zoysia grass is a warm season grass that is used as a sod turf grass in many home lawns. Crabgrass is a warm season annual that is highly invasive and lives in most lawns. Zoysia grass is slow growing and does not recover well from damage, according to the Texas A&M University Extension. When a lawn is highly damaged or overrun with crabgrass, you may need to start the entire lawn over by eradicating both the crabgrass as well as the zoysia grass.
Apply a pre-emergent herbicide two weeks before crabgrass seed germination in early April according to the packaging instructions. Crabgrass pre-emergent herbicides are often packaged as "crabgrass preventors".
Spray the areas with existing zoysia grass and crabgrass with a post-emergent herbicide containing glyphosate using an herbicide sprayer. Spray when there is no wind and no forecast of rain to prevent leaching and herbicides blowing in the wind. Wear safety goggles and long clothing to prevent herbicide burns.
Reapply post-emergent herbicides to ensure grass and weeds are killed.
Allow the lawn time to lay fallow to allow the herbicides to wear off before replanting grass.