Feature
Can We Control Weeds in St. Augustine? By Jeffrey Derr, Ph.D. and Adam Nichols
At
our research station located in southeastern Virginia, we receive questions about weed control in certain warmseason turf species that are not grown in western parts of the state. One common lawn species in our area is St. Augustine. It tolerates the heat and drought of summer and has better shade tolerance than bermudagrass or zoysia. We have evaluated cold tolerance in St. Augustine cultivars through an NTEP project. Although we have seen significant winter damage in certain St. Augustine cultivars, some, such as the Raleigh types, generally tolerate the winter temperatures we see in Hampton Roads. Weed control, however, is a challenge in this turf species. In this article we will discuss current suggestions for controlling grass, sedge, and broadleaf weeds in St. Augustine, as well as some of the research we are currently conducting. Although you may not be maintaining St. Augustine, some of the treatments we are evaluating are proving useful in other turf species and thus may benefit your program. Herbicide tolerance in St. Augustine: There are some common turf herbicides that cannot be used in St. Augustine due to severe injury. Drive (quinclorac) and products containing quinclorac cannot be used in this turf species. MSMA, currently registered for golf course, sod, and rights-of-way use, also causes severe injury to St. Augustine. The sulfonylurea herbicides Monument (trifloxysulfuron), Revolver (foramsulfuron), and Katana (flazasulfuron) are not registered for use in this turf species. Since St. Augustine has overall lower herbicide tolerance than bermudagrass and zoysia, one needs to pay special attention to rates when making applications. Often application rates are lower for St. Augustine than other turf species. Treating small
Bermuda Strip in St. Augustine
areas first to gain knowledge of turf tolerance when working with a new herbicide or herbicide formulation in St. Augustine is a good and safe practice. Annual grass control preemergence: In established St. Augustine we can use the preemergence crabgrass preventers used in other turf species. For example, prodiamine (Barricade, others), oxadiazon (Ronstar), benefin (Balan), bensulide (Bensumec), pendimethalin (Pendulum, others), dimethenamid (Tower), dithiopyr (Dimension), napropamide (Devrinol), and indaziflam (Specticle) can all be applied to St. Augustine. Read the label, though, as some of these chemicals, such as oxadiazon, cannot be used on home lawns. Also, sprayable formulations of oxadiazon can only be applied to dormant St. Augustine. These crabgrass preventers herbicides can also be applied in August for preemergence control of annual bluegrass as well as control of common chickweed and certain other winter annual broadleaf weeds. Use lower rates of indaziflam on St. Augustine compared to bermudagrass due to injury concerns. There is a combination product available that combines prodiamine, simazine, and imazaquin (Coastal Herbicide). This product will provide preemergence control of a range of annual grass and broadleaf weeds as well as early postemergence control of certain weeds, such as annual bluegrass. St. Augustine will probably be dormant when the application needs to be made for preemergence crabgrass control. If there was any winter kill, these preemergence herbicides will prevent the pegging down of St. Augustine stolons that try to fill in dead areas. St. Augustine does not produce rhizomes so it is dependent on spread through stolons to cover an area.
16 | VIRGINIA TURFGRASS JOURNAL November/December 2023 www.vaturf.org
