Carpet grass, known botanically as Axonopus affinis and St. Augustine grass, known botanically as Stenotaphrum secundatum, are both warm-season, perennial lawn grasses. Although healthy St. Augustine grass can usually fight off large-scale invasions of other grassy weeds, if the base lawn has been weakened, carpet grass can establish itself. A combination of good cultural practices and careful use of a non-selective herbicide can help manage and limit the infestation over time.
Apply a non-selective, post-emergent, contact herbicide product designed to kill any perennial grass weeds with which it comes into direct contact. Do not use systemic, non-selective herbicides because these will do more damage to the surrounding St. Augustine grass.
Time the application in the late spring or summer, to coincide with the most active growth period of the weed known as first flowering, before the seed heads develop.
Apply the spray product as recommended on the product label. Focus the spray stream at the center of the individual carpet grass plant, over the main roots. Use a narrow stream, to avoid over spray or splashing onto the surrounding St. Augustine grass. Do not exceed an application rate of 2 gallons of herbicide for every 1,000 square feet of carpet grass to be covered.
Repeat as recommended by the product label and as needed to control the carpet grass plants in your St. Augustine lawn.