Dollarweed, also known as pennywort, is a warm season weed that gets its name from the silver dollar-like shape of its leaf. Dollarweed is dark green and resembles a tiny lily pad. It spreads by seeds, rhizomes and tubers. Dollarweed is a water-loving plant and can float. When it is found in St. Augustine grass, this is an indication of high levels of moisture in the turf. Dollarweed can be controlled in St. Augustine grass by different methods. Like with many weed controls, it is very difficult to completely get rid of dollarweed.
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Pull the dollarweed plants from the ground. Dollarweed can be easily pulled by hand if infestation is not out of control.
Reduce the frequency of watering the St. Augustine grass. According to the University of Florida IFAS, research done in 2002 found that reducing irrigation cuts back on dollarweed infestation and its spread in St. Augustine since the weed thrives in moist conditions.
Apply an herbicide like atrazine. Atrazine should be applied twice a year, once in the fall and then in late spring. Atrazine is a pre- and post-emergent, which means it controls emerging weeds and weed seed. According to the Clemson Cooperative Extension, a three-way herbicide that contains 2,4- D, dicamba and MCPP can also be used safely on St. Augustine but in reduced rates. Imazaquin is another herbicide that can also be applied safely. Check with a specialty pest control store or lawn professional for other chemicals that can be applied.