How to Get Rid of Weeds in St. Augustine Grass
First determine whether the unwanted plant is actually a weed and why the turf is thinning. Shade, incorrect mowing height, moisture stress, excess moisture, compacted soil, insects, or disease can look like a simple weed problem but require a different response.
Work through the diagnosis before a pesticide
For a small infestation, physical removal may be practical. For a larger or uncertain problem, identify the target plant and read the complete current product label. The label must allow both the weed and the St. Augustinegrass cultivar, and its temperature, moisture, timing, rate, and safety instructions control the application.
UF/IFAS notes that chemical choices for St. Augustinegrass can be limited by grass maturity, stress, and product directions. Its Florida lawn weed-management guide also advises against treating an entire lawn with a weed-and-feed product when the infestation is limited.
Protect turf and nearby areas
Avoid moving an herbicide decision into planting beds or water. This guide does not prescribe an active ingredient, rate, application date, or outcome. Contact local Extension or a properly qualified applicator for an uncertain infestation. Spiced Up Lawn Service lists lawn maintenance, not a verified weed-treatment program.
Take identification notes
Photograph the plant before removal and note where it is growing, whether the turf is thinning, recent mowing changes, standing water, and seasonal timing. An identification question with those observations is more useful than trying to match a product to an unknown plant.