Things You'll Need
Shovel or garden spade
Broad-spectrum weed killer (optional)
Selective broadleaf herbicide
Virginia buttonweed belongs to the plant species Diodia virgniniana, hardy to U.S. Department of Agriculture plant hardiness zone 9, and is regarded as one of the most difficult broadleaf weeds to get rid of in turfgrass. What is Virginia buttonweed? Virginia buttonweed spreads both by seed and vegetative reproduction via spreading rhizomes. The weed is a vigorous grower and easily withstands very close mowing.
Even in healthy, established St. Augustine grass (Stenotaphrum secundatum, USDA zones 7 to 11) lawns, Virginia buttonweed can invade and form a dense mat of weeds. Here are some methods to control Virginia buttonweed in your St. Augustine grass.
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Step 1: Identify Virginia Buttonweed
Confirm that you indeed have Virginia buttonweed in your St. Augustine grass lawn. You can identify Virginia buttonweed by its oppositely arranged leaves that are connected by a membrane across the stem with several bristly stipules. The leaves are stemless, up to 2 1/2 inches long and 1 inch wide. In summer, Virginia buttonweed blooms with white, star-shaped, hairy, four-petal flowers that are stemless and 1/2 inch long.
Step 2: Pull Weeds by Hand
Hand-pull the Virginia buttonweeds if you have only small infestations or individual plants in your St. Augustine grass. Destroy the weeds and dig up the entire root system, without leaving any roots, rhizomes or other plant parts behind.
Step 3: Spray With Nonselective Herbicide
Spray the individual Virginia buttonweeds with a broad-spectrum herbicide like Roundup, if you have only a few isolated weeds in your St. Augustine grass. Beware that applying a broad-spectrum weed killer will also kill the grass with which it comes into contact. Avoid spraying the surrounding lawn area, and follow the directions on the herbicide label.
Step 4: Spray Lawn With Selective Herbicide
Apply a selective broadleaf weed killer for St. Augustine grass like one containing 2,4-D, dicamba, MCPP or MCPA to your lawn to control Virginia buttonweed that's more widespread in your lawn. Postemergence herbicides are generally more effective against Virginia buttonweed compared to preemergence herbicides. Follow the directions on the herbicide label carefully, ensuring the product you select is safe for your turfgrass and effective against broadleaf weeds like Virginia buttonweed.
Perform repeat treatments every two to three weeks as needed. To prevent damage to your St. Augustine grass, apply the herbicide during spring or early summer when temperatures are cooler.
Herbicides that are effective against Virginia buttonweed include the brand names Escalade II, Millennium Ultra 2, Powerzone, Momentum fx2, Surge, Speedzone, Three-Way Selective, Triplet and Trimec Southern. Read the labels on these products carefully to ensure that they’re safe for use on St. Augustine grass lawns, as some versions of the products may not be appropriate for certain turfgrasses.
Beware that mowing won’t control Virginia buttonweed in your St. Augustine grass lawn, even if you set the mower height to the lowest or closest blade setting. You can, however, control the moisture-loving Virginia buttonweed by not overwatering your St. Augustine grass and correcting any low areas in your lawn where water pools.