Weed Avengers: Weeds that come with higher temperatures

Seeing stars Virginia buttonweed features thickened leaves, hairy stems and white flowers with star-shaped petals. (Photo: PBI-Gordon)

Fire up the grill and get out all the poolside umbrellas — as of June 20 summer is officially here. With the temperatures climbing, it’s the right time to take a look at some weeds that don’t mind being late to the party. We consulted with three experts: Eric Reasor, Ph.D., research scientist, PBI-Gordon; Todd Lowe, Bayer Green Solutions Team technical service manager for the Florida region; and Dean Mosdell, Ph.D., technical manager, Syngenta Professional Solutions, to discuss spurge and Virginia buttonweed.

Spotted and prostrate spurge

Spotted spurge (Chamaesyce maculata L.) and prostrate spurge (Chamaesyce humistrata) are small, low-growing summer annual broadleaf weeds with central taproots and freely branched prostrate, mat-forming stems. “Stems are smooth and hairy, with ‘milky’ sap when broken,” Lowe says. “Spurges are common weeds in weakened turf, especially turf stressed by plant-parasitic nematodes.”

Spotting the spurge Spurge appears
close to sidewalks and driveways and
in weakened turf. (Photo: Syngenta)

Seedings may first appear next to driveways and sidewalks in home lawns. “Early applications of preemergence herbicides may only partially control spurge,” Mosdell says. “Split applications of preemergence herbicides like prodiamine will control prostrate spurge, paying close attention to applications next to walkways and driveways. Postemergence herbicides that contain dicamba are effective along with several three- and four-way mixtures. In Bermudagrass, (trifloxysulfuron-sodium) can be an effective tool to control spurge in addition to nutsedge and kyllinga.”

Lowe advises cultural practices like increasing fertilization and irrigation as well as reducing other stresses to help discourage spurges, and he echoes Mosdell in that multiple applications may be needed to control this pesky weed.

Virginia buttonweed

Another late-summer weed is Virginia buttonweed (Diodia virginiana L.), which can be found from New Jersey to Missouri and throughout the southeastern states. Virginia buttonweed has thickened leaves, hairy stems and white flowers with star-shaped petals.

“(Virginia buttonweed) likes low mowing, so mowing heights are important, and it likes wet conditions,” Reasor says. “It’s really slushy and succulent, which makes it hard to control. Any herbicide you use, the addition of a surfactant will help. It’ll follow the same category of herbicide use as spurge — your traditional three-way herbicides, it’ll take a little more than that. The herbicides that are great on dandelions, clover, plantains, that are relatively easy to kill? Buttonweed is harder to kill and a lot of times, it takes two applications.”

Reasor suggests fluroxypyr, triclopyr or metsulfuron in cool-season grasses and trifloxysulfuron in warm-season turf. “But again, a big part of controlling buttonweed is in mowing height and irrigation,” he adds.