Zoysia is a species of warm season, perennial lawn grass known for its stiff blades, tolerance for drought and foot traffic and a relatively slow growth habit. When zoysia is invaded by bermuda grass, another warm season perennial grass, it can be challenging to eradicate, according to the University of California Davis. Optimal maintenance practices that benefit the zoysia as well as judicious use of herbicides can help to check and manage the bermuda grass infestation. A healthy a vigorous zoysia lawn is the best defense against bermuda grass or any other invasive species.
Water your zoysia lawn deeply but infrequently to benefit the zoysia and create a bit of stress on the bermuda grass which prefers more frequent watering. Water may be needed once every 5 days in warm or very dry weather or every 8 days or longer in rainy and cool conditions. Water in the morning hours to prevent moisture loss to evaporation. Drench the soil with each watering to a depth of 4 to 6-inches, saturating the main root zone of the zoysia.
Establish a regimen of hand weeding the larger bermuda grass plants in the lawn, after each time you water. The plants come out by the roots and rhizomes more readily when being pulled from wet soil. Consistent thinning of the bermuda plants by weeding will help to get a handle on the infestation without chemical intervention, or as an adjunct to herbicide use.
Fertilize your zoysia lawn to keep it healthy and growing as vigorously as possible with a complete lawn fertilizer product with a guaranteed analysis of 30-15-15 or a similar ratio of macro nutrients. Feed once per month from May through August, according to the product label directions but not exceeding two pounds of actual nitrogen for every 1,000 square feet of lawn expanse. Cast the fertilizer evenly over the lawn and water in well to wash the grains down to the thatch and into root zone.
Spray actively growing bermuda grass plants with a non-selective, post emergent herbicide that kills the portions of the plant it comes into contact with. Choose an herbicide product containing the active ingredient diquat, pelargonic acid or glufosinate. Spray the bermuda plants directly over their crown and leaves with a narrow stream of liquid preventing splashing and over spray onto your zoysia. Apply according to the product label directions and repeat as needed throughout the growing season to control the bermuda grass.
Mow your zoysia lawn within the range of its ideal blade length, between 1 and 2 1/2-inches. Always mow with the catcher in place to prevent the clippings from building up as thatch. More importantly, the catcher will collect any Bermuda stolon pieces and seed heads, preventing them from being re-distributed over the lawn where they will germinate and grow, perpetuating the problem.