Bermuda grass (Cynodon dactylon) invading a Zoysia lawn (Zoysia spp.) is a challenging turf management problem. Both are warm-season grasses sharing a similar C-4 photosynthetic pathway, which complicates selective chemical control. Successfully removing the aggressive Bermuda grass requires a multi-faceted strategy combining careful identification, precise cultural practices, and targeted herbicide application. The goal is to eliminate the invader without causing lasting damage to the desirable Zoysia turf.
Distinguishing Bermuda Grass from Zoysia
Identifying the invading grass is the first step toward effective removal. Bermuda grass has a fine texture, with narrow leaf blades typically measuring 1.5 to 2 millimeters in width. It spreads rapidly through above-ground runners (stolons) and below-ground stems (rhizomes).
Zoysia grass possesses a coarser texture with wider leaf blades, ranging from 2 to 7 millimeters depending on the cultivar. Although Zoysia uses stolons and rhizomes, its lateral spread is significantly slower and less aggressive than Bermuda grass. The Zoysia canopy forms a dense turf, but its slower recovery makes it vulnerable during initial Bermuda intrusion.
Bermuda grass is typically a bright, light green color and thrives exclusively in full sun. Zoysia often has a darker green hue and exhibits better tolerance for partial shade. Bermuda grass requires much more frequent mowing due to its rapid vertical and horizontal growth.
Manual and Cultural Control Strategies
Non-chemical control methods exploit the biological differences between the grasses to suppress the invader.
Mowing Height
Adjusting the mowing height is a powerful cultural tool to favor Zoysia. Mowing Zoysia at the higher end of its recommended range, typically between 1.5 and 2 inches, allows it to develop a deeper canopy. This increased height effectively shades the lower-growing Bermuda grass, limiting the sunlight it needs to thrive and spread. Bagging the clippings is also important, as this practice prevents the unintentional redistribution of any Bermuda grass seed heads. Avoid mowing too low, as this favors the prostrate growth habit of Bermuda grass.
Watering Practices
Watering practices should promote deep Zoysia root growth, which disadvantages the shallow Bermuda grass. Deep, infrequent irrigation, supplying about one inch of water per week, encourages a resilient Zoysia root system. Avoiding shallow, frequent watering is important because it keeps the surface moist, which is conducive to the rapid spread of Bermuda’s surface stolons.
Fertility Management
Fertility management shifts the competitive balance. Bermuda grass requires high levels of nitrogen for aggressive growth. By reducing the annual nitrogen input to the lower range recommended for Zoysia (typically 2 to 3 pounds of actual nitrogen per 1,000 square feet), the lawn’s health is maintained while slowing the Bermuda grass’s spread.
Manual Removal
Manual removal is practical only for very small, isolated patches. When hand-pulling, remove both surface runners and the extensive below-ground rhizomes. Because Bermuda grass can regenerate from small fragments of these underground stems, manual control is rarely effective for larger infestations.
Selective Herbicide Application Techniques
Chemical control is necessary for significant Bermuda grass invasions, requiring selective post-emergent herbicides that target the invader while sparing the Zoysia. The most effective active ingredients are fluazifop (often sold as Fusilade II) and fenoxaprop. These chemicals are grass-selective herbicides that inhibit fatty acid synthesis in the target plant.
Timing and Application
Herbicide application must coincide with the active growth of Bermuda grass, typically from late spring through late summer when soil temperatures are warm. Applying the herbicide when Bermuda grass is dormant or stressed results in poor control. Wait until the Zoysia is fully greened up and actively growing before beginning treatments.
Complete elimination requires a sequence of multiple, low-dose applications rather than a single treatment. Four to five sequential applications, spaced three to four weeks apart, achieve the highest control rates. This repeated assault is necessary to deplete the energy reserves stored in the Bermuda grass’s extensive rhizome system.
Managing Zoysia Injury
Fluazifop and fenoxaprop can cause temporary injury to the Zoysia turf, often appearing as slight yellowing or discoloration. Zoysia generally recovers fully, but this temporary phytotoxicity is a trade-off for effective control. Some professional products combine fluazifop with a chemical safener, such as metcamifen, allowing for a higher dose with reduced risk of Zoysia injury.
Application Requirements
The inclusion of a non-ionic surfactant in the spray mixture is essential to ensure the herbicide effectively penetrates the waxy leaf surface of the Bermuda grass. Application rates must strictly adhere to the product label. Rates that are too low will not control the Bermuda grass, and rates that are too high will severely damage the Zoysia. For certain Zoysia cultivars, the addition of triclopyr can enhance the safety of fluazifop and fenoxaprop applications by reducing the risk of Zoysia injury.
Promoting Zoysia Density for Long-Term Control
Once Bermuda grass is suppressed, focus shifts to creating a dense, healthy Zoysia stand that resists re-infestation. A thick Zoysia canopy is the lawn’s best defense against future weed seed germination. Density is achieved through a tailored fertility and maintenance program.
Fertility and Thatch Management
Fertilizer applications should utilize slow-release nitrogen sources to minimize sudden growth surges. Applying 1 to 2 pounds of nitrogen per 1,000 square feet annually, divided into multiple applications during the summer, provides consistent nutrition. This moderate approach encourages Zoysia to spread and thicken laterally.
Zoysia produces a significant amount of thatch—a layer of organic debris—due to its dense growth habit. Periodic dethatching or aeration is necessary to prevent this layer from impeding water and nutrient movement. Perform these actions in the late spring or early summer when the grass is actively growing to ensure quick recovery.
Preventive Measures
Integrating a pre-emergent herbicide into the annual maintenance calendar is a highly effective preventive measure. Applying a pre-emergent in late winter or early spring creates a chemical barrier that stops new weed seeds, including Bermuda grass, from germinating. This proactive approach sustains the Zoysia’s dominance.