Speedzone Lawn and Weed Killer is not labeled for use on St Augustine and most likely would cause damage if used on St Augustine lawns. Speedzone Southern is labeled for Dollarweed and for use on St Augustine grass. According to the Speedzone Southern product label: The turf tolerance to this product may vary and temporary turf grass yellowing may occur on St Augustine. Do not apply Speedzone Southern to Floratam, Bitterblue or other improved species of St Augustine. Do not broadcast or spot spray St Augustine during the fall to winter transition or if temperatures are expected to fall below 40F within 10 days of the application.
Please take a few moments to read through the product label completely for full instructions and other precautions.
SpeedZone Lawn Weed Killer Concentrate does contain a surfactant and additional one is not required for use with it. The SpeedZone Red which is very similar to the Lawn Weed Killer does state on the product label that adding one may reduce the selectivity on the turfgrass so it could harm your lawn in adding one.
SpeedZone Lawn Weed Killer Concentrate - 20 oz. cannot be used on St. Augustine grass. Speedzone Southern, you can use.