ANNUAL GRASSES
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. So, if you have observed unusually low temperatures during the winter, or a rapid decrease in temperature as we observed in the winter of 2022-2023, you may want to hold off on application of a crabgrass preventer until St. Augustine has greened up and any winter damage will be apparent. The problem with that approach, though, is that crabgrass probably has started germinating before St. Augustine is fully greened up. There are limited options for postemergence crabgrass control in this turf species.
Annual grass control postemergence: Atrazine (Aatrex, others), sulfosulfuron (Certainty) and amicarbazone (Xonerate) are options for postemergence annual bluegrass control. The Certainty label cautions users, though, to test this product on small areas first as St. Augustine is less tolerant compared to other warm-season turf species such as bermudagrass.
Postemergence crabgrass control: This is a challenge. Dimension and Celsius will control pre-tillered crabgrass and atrazine will suppress this weed. Xonerate will suppress crabgrass but the label warns against summer applications when temperatures are high. Other postemergence crabgrass herbicides used in other turf species, such as quinclorac, will damage St. Augustine.
