Bermuda grass is an aggressive, warm-season turf that can quickly invade and overtake a desirable St. Augustine lawn. This invasion creates a patchy, uneven appearance where the fine-bladed Bermuda grass competes directly with the thick-bladed St. Augustine. Selective removal is challenging because both are members of the grass family. The goal is to employ targeted strategies that exploit the subtle differences between these two grasses to suppress the aggressive invader without harming the desired turf.
Why Selective Removal is Difficult
The difficulty in separating Bermuda grass from St. Augustine grass stems from the fact that both are warm-season grasses. This shared characteristic means that most non-selective herbicides will kill both the weed and the desirable lawn simultaneously. The chemical makeup that targets one grass often targets the other, presenting a major hurdle for homeowners trying to spot-treat an infestation.
Bermuda grass possesses an aggressive growth habit involving both above-ground runners (stolons) and robust underground stems (rhizomes). These structural components allow it to spread rapidly and regenerate quickly after being damaged. Removing visible surface runners through mowing or hand-pulling is often ineffective because the plant can sprout anew from the extensive, unseen network of rhizomes beneath the soil. Even small fragments of these underground stems can lead to a new outbreak, making complete manual eradication nearly impossible once the infestation is established.
Targeted Chemical Suppression Methods
Effective chemical control relies on using specialized products that the St. Augustine turf can tolerate. A highly-specific method involves combining herbicides, typically pairing a product like Fusilade II with a proprietary “safener” found in herbicides such as Recognition. The safener, often metcamifen, allows St. Augustine grass to withstand the effects of Fusilade II, while the Bermuda grass remains susceptible to the treatment.
This two-part herbicide approach allows for the elimination of Bermuda grass without causing serious injury to the surrounding St. Augustine. Application should be timed when the Bermuda grass is actively growing, typically from late spring to early summer, ensuring the plant absorbs the chemical effectively. It is recommended to include a non-ionic surfactant in the spray mixture to help the herbicide adhere to the waxy leaf surfaces for better absorption.
Multiple applications are necessary to achieve satisfactory control because the rhizome network requires repeated exposure to fully deplete the plant’s energy reserves. The second application is typically performed four to six weeks after the first, depending on the visible regrowth of the Bermuda grass. Homeowners must use a calibrated sprayer for accurate spot-treatment, as hose-end applicators do not offer the precision needed for these specialized chemicals.
Non-Chemical and Cultural Control
Non-chemical methods are best suited for smaller, isolated patches or for homeowners who prefer to avoid herbicides entirely. Physical removal requires digging up the entire root system, including all visible stolons and the underground rhizomes, which is a labor-intensive process. It is crucial that the soil is moist when attempting hand-pulling, as this makes it easier to extract the complete root structure and minimize the chance of leaving regenerative fragments behind.
For heavily infested, localized areas where the St. Augustine grass is already sparse, solarization can be an effective, non-chemical option. This technique involves covering the affected area with a clear plastic sheet for four to six weeks during the hottest part of the year. The trapped solar heat raises the soil temperature high enough to kill the Bermuda grass and its rhizomes, although this will also kill the St. Augustine grass in the treated section, requiring subsequent reseeding or re-sodding.
Cultural practices can weaken and suppress Bermuda grass by favoring the St. Augustine turf. Bermuda grass prefers to be mowed very low, often under two inches, while St. Augustine thrives at a much higher height. Raising the mowing height to between 3.5 and 4 inches helps the St. Augustine grass shade out the lower-growing Bermuda grass, starving it of the full sunlight required for aggressive growth.
Long-Term Prevention of Reinfestation
Maintaining a dense, healthy St. Augustine lawn is the most effective long-term defense against Bermuda grass reinfestation. A thick turf minimizes the open spaces and bare soil that Bermuda grass seeds and runners need to establish themselves. This density is achieved through proper fertilization, specifically using a slow-release nitrogen formula that supports the St. Augustine without overly stimulating the Bermuda grass.
Appropriate irrigation practices also favor the desired turf. St. Augustine benefits from infrequent, deep watering, which encourages deep root growth. Bermuda grass, being more drought-tolerant, can survive on minimal moisture, so avoiding frequent, light watering strengthens the St. Augustine’s competitive advantage. Consistent monitoring is necessary, and any new Bermuda grass should be spot-treated immediately before it can establish a new network of stolons and rhizomes.
Physical barriers play a significant role in preventing the spread of Bermuda grass from adjacent areas, such as neighboring lawns or garden beds. Installing landscape edging or a similar physical barrier along the perimeter can stop the aggressive surface runners from creeping into the St. Augustine lawn. Applying pre-emergent herbicides annually also helps by creating a chemical barrier that prevents wind-blown Bermuda grass seeds from germinating in the soil.