Perennial grass control. Not too many options here. Atrazine could be used for suppression of actively growing bermudagrass as well as removal of cool-season grasses like tall fescue. We have also evaluated Prograss for bermudagrass suppression. Based on our work, with some assistance from these chemical treatments, St. Augustine appears to be able to outcompete bermudagrass. We have evaluated the addition of mesotrione (Tenacity) to atrazine, which has a synergistic benefit but Tenacity is only registered for St. Augustine grown for sod. Certainty suppresses dallisgrass and controls cool-season grasses like ryegrass and tall fescue but check the tolerance on a small area first.
Preemergence annual broadleaf control: Both atrazine and simazine (Princep) provide control of many broadleaf weeds at germination. Isoxaben (Gallery) will also control a wide range of annual broadleaf weeds, especially winter annuals.
Postemergence broadleaf control: St. Augustine is sensitive to some of the postemergence broadleaf herbicides used in turf, such as 2,4-D. Products for use in use in sensitive southern grasses such as St. Augustine utilize reduced rates of the broadleaf herbicides. For example, Speedzone EW, which is not labeled for use in St. Augustine, contains 1.27 pounds 2,4-D and 0.12 pounds dicamba per gallon while Speedzone Southern EW, which is labeled, contains 0.51 pounds 2,4-D and 0.05 pounds dicamba per gallon. The two products have a similar use rate (pints per acre).
One product we regularly use for broadleaf control in St. Augustine is Celsius, which has 3 active ingredients: iodosulfuron, thiencarbazone, and dicamba. It controls a wide range of broadleaf weed and certain annual grasses. Celsius XTRA is a similar product that also contains iodosulfuron and thiencarbazone but instead of dicamba it contains halosulfuron. Halosulfuron is the active ingredient in SedgeHammer and ProSedge. So Celsius may be the preferred product if only broadleaf weeds are present. Celsius XTRA would be the better choice if one is trying to control both broadleaf weeds and yellow nutsedge. Another combination product where acceptable tolerance exists in St. Augustine is Avenue South, which contains 2,4-D, dicamba, penoxsulam, and sulfentrazone. St. Augustine does not possess acceptable tolerance to Tribute Total, which contains foramsulfuron, halosulfuron, and thiencarbazone..
We would like to be able to recommend an effective postemergence broadleaf herbicide for all warm season and cool-season turf species, especially in our areas due to the variety of turf species being maintained. Unfortunately, we have not identified a product that fits this need. One of the limiting species is St. Augustine, where products containing higher rates of 2,4-D can be injurious, and products containing lower doses of 2,4-D and related herbicides are less effective for weed control. The other limiting species is tall fescue, where Avenue South can be injurious, and other products such as Celsius and Certainty cannot be used.
Yellow nutsedge control: Celsius XTRA, sulfentrazone (Dismiss), halosulfuron, Certainty, Basagran and Vexis are options for control of emerged yellow nutsedge and other sedges. Tower is a possibility for preemergence yellow nutsedge control but we have not evaluated it in St. Augustine. We have observed delayed greenup in bermudagrass with this product.
Current research – Recognition: The active ingredient in Monument is trifloxysulfuron but Monument cannot be used in St. Augustine due to injury. Recognition also contains trifloxysulfuron but along with this active ingredient it also contains a safener, metcamifen, that increases the tolerance in St. Augustine and certain other grasses. Besides increasing tolerance to sulfonylurea herbicides like trifloxysulfuron, it increases the tolerance in St. Augustine to the postemergence broadleaf herbicide like triclopyr (Turflon Ester), post grass herbicides like fluazifop (Fusilade), and bleaching herbicides like Tenacity.
We have seen a slight off-color to St. Augustine following a Recognition application but the turf outgrows this effect fairly quickly. So, Recognition, according to the label, is an option in St. Augustine for control of ryegrass, a range of broadleaf weeds, and yellow nutsedge, as well as dallisgrass suppression. We are currently conducting research to determine if Recognition is as effective as Monument on a variety of weed species as it is possible the safener in Recognition could also increase herbicide tolerance in weed species.
We have evaluated Recognition plus Fusilade for suppression of bermudagrass, as well as Recognition plus Turflon Ester for improved broadleaf control and bermudagrass suppression. Although multiple applications will probably be required to eradicate bermudagrass, the bermudagrass suppression makes St. Augustine more competitive. Recognition plus Tenacity has shown promise for control of doveweed and crabgrass.
We also see potential for Recognition plus Fusilade for improved bermudagrass control in zoysia. We have evaluated adding 24 fluid ounces per acre of Fusilade with Recognition. This rate of Fusilade is much higher than can be applied with Fusilade alone in zoysia, showing the benefit of the safener metcamifen. Use of higher rates due to the safener allows for better bermudagrass control. Metcamifen does not appear to increase herbicide tolerance in bermudagrass. There should be similar benefits of Recognition plus Fusilade for control of dallisgrass. We plan to continue our research with Recognition and Recognition combinations in St. Augustine and zoysia.
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Jeffrey Derr and Adam Nichols are located at Virginia Tech’s Hampton Roads Agricultural Research and Extension Center in Virginia Beach.
