Q: We have a ninety-five percent zoysia lawn. Some bermuda has infiltrated the zoysia. What is the best way to eliminate the bermuda?

A: My neighbor has a thin-bladed zoysia (maybe ‘Emerald’) that has gradually overcome the bermudagrass in his lawn in the past decade. The same thing happened on my parents’ lawn. My guess is that wider-bladed zoysia (‘Meyer’, etc) is less competitive with bermudagrass than the thin-bladed plant is, thus explaining why your zoysia hasn’t prevailed. For quick results you could spray the intermingled area with glyphosate (click for sources)  and re-sod with zoysia.

There are a couple of herbicides that weaken bermudagrass in zoysiagrass lawns but they take years to show much effect.