Ronald Strahan | 7/26/2016 5:25:35 PM
Virginia buttonweed is widely considered the most invasive weed infesting turfgrass in the South. The plant is extremely prolific and has multiple ways to reproduce, including heavy seed production that occurs both above and below the ground from self-pollinating flowers, rooting stem fragments and tap roots that allow plants to survive through winter. Mowers set at even the lowest blade height do not interfere with growth or seed production of this plant.
Because of the potential for stem fragments to root, mowing may actually aid in the spread of buttonweed. Turning the mower deck discharge toward landscape beds could even start populations of buttonweed in flower beds.
Virginia buttonweed control
Virginia buttonweed is tolerant of most selective herbicides used for weed control in turf, especially when plants harden off in late summer. Managing the weed should start early in spring as perennial plants emerge from winter dormancy.
April and May are good months to begin spraying buttonweed in spot applications. Perennial plants that went dormant after the first frost will begin emerging in early April. Seedling plants germinate around the perennial “mother” plants as temperatures warm in spring. During this early growing season, perennial plants are tender with new growth. It is at this time that the perennial plants are most susceptible to herbicide uptake. Additionally, herbicide applications during spring will easily kill germinating seedling plants and reduce the overall buttonweed population significantly.
The worst thing to do is to wait until late July or August to make the first herbicide application. By late summer, heavy Virginia buttonweed populations can form a dense mat that can kill large areas of the lawn. Single herbicide applications, especially late-season, have not been effective on mature Virginia buttonweed. Multiple applications throughout the summer are needed after the initial spring applications to get buttonweed under control.
A program approach works best to control buttonweed. According to research trials conducted by the LSU AgCenter, herbicides that contain the active ingredients 2,4-D, dicamba, mecoprop and carfentrazone (Speed Zone Southern, Weed Free Zone, Weed B Gon) have been effective in suppressing emerging perennial plants and killing the first flush of buttonweed seedlings when applied in early spring. Once temperatures exceed 85 degrees, herbicides containing 2,4-D cause too much injury to St. Augustinegrass and centipedegrass.
In the hot summertime, metsulfuron (MSM, Mansion) or Celsius herbicides should be applied. Always repeat metsulfuron or Celsius applications four to six weeks after the initial application. Both Celsius and metsulfuron have performed well in research trials, and these herbicides seem to be tolerated pretty well by St. Augustinegrass even in hot weather.
Ron Strahan is a weed scientist and associate professor in the School of Plant, Environmental and Soil Sciences
Flowering buttonweed. Photo by Ron Strahan
Virginia buttonweed. Photo by Ron Strahan
Seedling buttonweed. Photo by Ron Strahan