Answer: Dollarweed, also called Pennywort, is a small broadleaf plant. The best way to get rid of it is to hand pull it from the root.The problem is that it grows in large patches and it replaces itself quickly so that few find pulling it up a reasonable solution. There are, however, a plethora of avenues of attack to try.
Try weed-killing chemicals. There are chemicals available including WipeOut by GreenLight which will kill the weeds but not their seeds so multiple applications will be needed. A product called Image is also an option. It's especially good for use with St. Augustine grass. The chemical of choice was Atrizine which has been banned as an herbicide by the EPA. You can still get the same chemical in weed and feed preparations and use that.
Use regular table sugar on the lawn. One pound should cover about 250 to 300 square feet. Put down your sugar and water it well and keep your lawn mowed as you usually do. Within a couple of weeks you should see fewer weeds.
Choose a natural weed killing herbicide whose main ingredient is 10 percent vinegar. You have to use 10 percent vinegar only--regular vinegar is of no use--check with your local nursery or gardening department. The formula for this is as follows: 1 gallon of 10 percent vinegar, 1 oz. orange oil, 1 tbsp. molasses (the ordinary kitchen type), 1 tsp. liquid soap. Shake well and use full strength on warm to hot days for best results. Don't spray on plants you want to keep alive as it will harm any plant it touches.
If all else fails, try the experts. If you're anywhere near a university they usually have an extension service that provides information and assistance with tough yard and garden problems. They're also great for information on all kinds of kitchen safety, pest problems, and soil testing.
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