Answer: There are broadleafed weed killers that spare grasses, and grass killers that spare broadleaf plants. There are also herbicides that kill all vegetation. There have been dozens of articles written about the pros and cons of each. But the bottom line is that you'll need to employ several strategies all at once to keep weeds out of your St. Augustine. Begin by removing all visible weeds, then applying a pre-emergent with a corn gluten base. Corn gluten produces an enzyme that inhibits seed germination, and can be used as a preemergent herbicide. If the weeds in your lawn are coming up from seed, then corn gluten is for you! General home lawn broadleaf weed control can often be accomplished using selective postemergence formulations. Formulations are available for most southern grasses. Examples are Green Light Wipe-out, K-Mart Broadleaf Weed Killer for Southern Grasses, Spectrum 33 Plus, Trimec, Ferti-lome Weed Out and Ortho Weed-B-Gon II for Southern Grasses. To be on the safe side, make sure St. Augustine is listed on the label. If not, the herbicide will kill your St. Augustine along with the weeds.
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