How to Get Rid of Dollarweed in St. Augustine Grass

University of Florida Gardening Solutions describes dollarweed as a low broadleaf weed of wet places. One round leaf sits on each stalk. The leaf can grow about as big as a silver dollar, which is the common name, and it looks like a small lily pad. The stalk attaches in the center of the leaf, so the leaf sits like an umbrella. That center attachment is how you separate it from dichondra, whose stalk attaches at the edge of the leaf.

It is a perennial. It comes back from rhizomes, the white underground stems, and also from seed. If you pull a leaf and leave the rhizome, you did not remove the plant. It is not nutsedge. Nutsedge has a triangular stem and a grass-like leaf. Both plants point at the same problem, a spot that stays moist, and UF lists both dollarweed and nutsedges among the weeds that show up when soil stays wet.

Dollarweed is a moisture indicator. UF says it appears where the lawn is overwatered or naturally soggy, and that overwatering also favors sedges. A healthy lawn, in UF's lawn-watering guidance, gets water when it shows stress: blades folding, a blue-gray color, footprints that stay. Each watering should be about 1/2 to 3/4 inch, then you wait until the stress signs come back. Light watering every day keeps the surface wet, roots shallow, and dollarweed comfortable.

On St. Augustine, which is the usual lawn under this weed in Florida and along the Gulf Coast, the irrigation timer is often the cause. The clock was set in July and never changed. Low spots, a leaking head, and a downspout that dumps into the turf do the same job. Spraying without changing the water is how the weed returns next month. The watering guide and the irrigation runtime calculator are the practical half of that.

Start with the water. Turn the schedule down or off until the St. Augustine actually needs a drink. Fix the leak, extend the downspout, and if a spot stays wet after a rain, that is a drainage problem, not a herbicide problem. UF says you can hand-pull dollarweed if you get the white rhizomes, not just the leaves. Small patches are worth pulling. A lawn full of it will also need a spray, and the spray still fails if the soil never dries.

For herbicide, UF's homeowner guide names two active ingredients that show up in lawn products aimed at this weed. Penoxsulam is often added to broadleaf herbicides to improve control of dollarweed. Imazaquin is used for dollarweed as well as for some sedges and other broadleaves. Gardening Solutions says either a selective or a non-selective herbicide can be used if you follow the label. Non-selective means it can kill the St. Augustine too, so that is a spot treatment with the grass shielded or avoided, not a blanket spray. Use a selective product whose label lists both dollarweed (or pennywort) and St. Augustine.

Spray while the weed is growing, in the warm season, on a lawn that is not wilted from drought. Rhizomes survive a timid spray, so the label's repeat interval is part of the plan. Then keep the new irrigation habit. A product that knocks the leaves down will not matter if the sprinklers run every morning.

Do not reach for a nutsedge-only herbicide and assume it covers this. Halosulfuron is the usual nutsedge active ingredient, and UF discusses it for sedges, not as the dollarweed answer. Imazaquin is the one UF lists for both jobs. Read the bottle.

• Watering St. Augustine every day, then spraying dollarweed, then watering every day again.
• Calling it dichondra. Look at where the stalk meets the leaf.
• Pulling leaves and leaving the white rhizomes.
• Using a nutsedge product that does not list dollarweed.
• Broadcasting a non-selective herbicide across the lawn.
• Treating dollarweed and nutsedge as one weed. They share a wet spot. They do not share every herbicide.