Carpet grass (Axonopus affinis) is a perennial turf variety known for its aggressive growth habit, allowing it to quickly dominate a lawn or landscape. This grass spreads rapidly through low-growing, above-ground runners called stolons, creating a dense, mat-like cover. Its persistence and ability to thrive in poor, acidic, and moist soils make it challenging to remove. Eradicating this weed requires a persistent, multi-step approach focused on eliminating the visible foliage and the extensive root and stolon system.
Non-Chemical Eradication Strategies
Methods that rely on physical removal or environmental deprivation offer an effective way to eliminate carpet grass without introducing chemical agents into the soil. These strategies are often slower than chemical treatments but can achieve complete control over time.
Solarization
Solarization uses heat to sterilize the top layer of soil where the weed’s seeds and shallow roots reside. To prepare, the area should be mowed as low as possible and then thoroughly watered to encourage active growth. A sheet of clear plastic, typically 4 to 6 millimeters thick, is then laid over the area, extending well past the infested edges. The edges must be completely secured by burying them or weighing them down to trap heat and moisture. This process typically requires four to eight weeks during the hottest part of the summer, depending heavily on local climate conditions and the intensity of direct sunlight.
Manual Removal
For smaller patches, manual removal is a precise but labor-intensive option. Because carpet grass is a perennial that can regrow from any remaining piece, it is necessary to dig deep enough to remove all connected stolons and any associated rhizomes. Any fragment left behind in the soil can quickly sprout a new plant, restarting the infestation.
Smothering
Smothering works by depriving the grass of the sunlight it needs for photosynthesis. This involves laying a thick layer of material, such as four to six layers of newspaper, heavy cardboard, or landscape fabric, over the infested area. The material should be covered with mulch for aesthetic purposes and to hold it in place. This method requires significant time, often taking several months to a full growing season to kill the persistent grass completely. Smothering is particularly useful for establishing new garden beds where a long period of soil rest is acceptable.
Targeted Herbicide Application
When speed and certainty of kill are prioritized, a chemical approach using herbicides is the most efficient method for large or severe infestations.
Non-Selective Herbicides
Non-selective herbicides, such as those containing glyphosate, are highly effective because they kill any plant tissue they contact. Glyphosate is a systemic herbicide absorbed through the foliage and translocated throughout the plant, including the stolons and roots. Because glyphosate kills all green plants, its application requires precision, often utilizing spot-treatment or wick applicators to avoid desirable turf or landscape plants. For widespread infestations, the entire area must be sacrificed to ensure a complete kill of the dense carpet grass matting.
Selective Herbicides and Timing
In situations where the desired turf must be protected, selective post-emergent herbicides can be used, though this is generally more difficult for carpet grass. Specialized products containing active ingredients like thiencarbazone, iodosulfuron, and dicamba (often sold commercially as Celsius WG) have shown good efficacy against Axonopus affinis. These products are formulated to target grassy weeds while minimizing damage to certain warm-season turf types.
The timing of the application is crucial for the herbicide to be effective. Herbicides must be applied during the grass’s active growth phase, typically in the late spring or summer, when the plant is moving nutrients and water from its leaves to its roots. This internal movement ensures the systemic chemical is transported to the underground stolons and rhizomes, leading to a complete kill. Due to the persistent nature of carpet grass, a single application is rarely sufficient for full eradication. Multiple treatments, usually spaced two to four weeks apart, are necessary to eliminate plants that may have been missed or that have regrown from surviving root fragments. Always ensure you are wearing appropriate personal protective equipment and apply the product on a calm day to prevent herbicide drift onto non-target plants.
Site Preparation and Post-Treatment Care
Proper preparation immediately before applying a systemic herbicide is necessary to maximize the chemical’s uptake and translocation. You should avoid mowing the area for at least two to three days prior to spraying to allow the maximum leaf surface area to be present. The large surface area is where the herbicide is absorbed, facilitating its movement throughout the plant’s vascular system. The area should also be adequately watered about 24 hours before the application to ensure the grass is actively growing and healthy. A well-hydrated, actively growing plant will more readily absorb and transport the herbicide to its root system, increasing the chemical’s effectiveness.
After the herbicide has had time to work, which may take up to two weeks, the dead, brown grass thatch must be thoroughly removed. This cleaning process clears the area of dead organic matter and prepares the soil for re-establishment of a desirable ground cover. The soil should then be lightly tilled or aerated to improve drainage and reduce compaction.
To prevent the carpet grass from returning, the long-term focus must shift to creating soil conditions that discourage its growth. Carpet grass thrives in acidic, low-fertility soils, so amending the area by adding agricultural lime to raise the soil pH to a more neutral level is highly beneficial. Incorporating organic matter and a balanced fertilizer into the topsoil will further promote a healthy environment for desirable plants.
The use of pre-emergent herbicides is an important step in long-term prevention, as they target any lingering seeds in the soil. These products must be applied before the carpet grass seeds germinate in the spring, typically when soil temperatures consistently reach 50 to 55 degrees Fahrenheit. Products containing active ingredients like Pendimethalin are often recommended for their effectiveness against carpet grass seedlings. Re-establishing the area with a dense, healthy lawn or groundcover will also naturally suppress any future weed growth.