Mississippi Turfgrass Association – St. Augustinegrass Management

July 18, 2019 | Mississippi Turfgrass Association | PODCAST

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Mississippi Turfgrass – Jay McCurdy, Ph.D., Maria Tomaso-Peterson Ph.D., and Wayne Philley Ph.D.

St. Augustinegrass (Stenotaphrum secundatum) is one of Mississippi’s most common turfgrass species, yet its culture and production in much of the south is fraught with difficulty. Here, we offer advice and considerations for St. Augustinegrass management in the mid- and deep-south.

The earliest documented case of St. Augustinegrass propagation as turfgrass is near Orange Park, Florida in 1880. It has since become a staple species for lawns and commercial properties throughout the southeast and other tropical and sub-tropical climates around the world. Although viable seed are often produced, commercial seed production has been limited throughout the history of the grass. Therefore, it is often established by plugs, sprigs, or sod, sometimes passed from neighbor to neighbor or relocated from original homesteads. (Fig. 1)

St. Augustinegrass is one of the few native species cultivated as turfgrass in the southeastern United States — another being various carpetgrasses (Axonopus species). St. Augustinegrass is known as “Charleston” grass to some and as “Buffalo” in Australia and the wider South Pacific. It spreads quickly by above ground stolons and forms a low-growing, dense turf with coarse-textured leaves. St. Augustinegrass performs well in full sun but is one of the most shade tolerant warm-season turfgrasses.

St. Augustinegrass is a prominent species along Mississippi’s gulf coast. It can also be found in older neighborhoods as far north as Memphis and Little Rock. The diverse climate regions of the southeast make St. Augustinegrass management challenging. Due to its tropical origins, St. Augustinegrass is well adapted to the humid climate and is tolerant of mild salinity and poor water quality. However, it lacks tolerance to freezing temperatures and can be difficult to maintain in northern areas of the state and region.

Because St. Augustinegrass lacks below ground rhizomes, its stoloniferous regrowth is vulnerable to harsh winter conditions. Most St. Augustinegrass varieties need approximately 200 frost free days. Note that frost free days do not trend horizontally northward. For instance, historically, Memphis has approximately 220 frost free days, while Corinth has 190, and Starkville has 200.

Some varieties of St. Augustinegrass are better adapted to cooler temperatures than others. For instance, ‘Floratam,’ is common in Florida and in areas of Mississippi south of Interstate-10, but it does not tolerate the frequent freezing temperatures in the rest of Mississippi. ‘Common’ St. Augustinegrass is probably the most prevalently produced in the state and region; however, the improved cultivars ‘Raleigh’ and ‘Palmetto’ are increasingly soughtafter for cold tolerance and resistance to disease and insect damage. Researchers at Mississippi State recently released the experimental cultivar ‘MSA 2-3-98’ for commercialization. It has cold tolerance equal to or greater than Raleigh with improved turf quality due to higher density and finer leaf texture.

Management Considerations

Is St. Augustinegrass the right choice? Although it does well in shaded scenarios, no turfgrass does well in absolute shade. Bermuda and zoysia grasses are more appropriate than St. Augustinegrass for high traffic scenarios. If you are parking cars or hosting back-yard weddings, St. Augustine is going to have a hard time recuperating.

Insects, such as southern chinch bugs, and diseases, like gray leaf spot and large patch can also devastate St. Augustinegrass. This can be especially evident while the grass is affected by other abiotic and biotic stresses (for example: shade, drought, herbicide injury, over-irrigation, improper fertility, traffic stress, etc.).

Fertility

There is no substitute for a proper soil analysis. But generally speaking, St. Augustinegrass needs far less nitrogen than the average lawn care company applies. Insects and diseases take advantage of over fertilized and over irrigated lawns. This is especially true for St. Augustinegrass. The northernmost lawns of the state need no more than two to three pounds of actual nitrogen per 1,000 ft2 per year. That number is slightly higher along the coast, but still, excessive fertility only breeds more problems. This amount can be reduced further by spoon feeding nutrients every few weeks throughout the growing season, or by using slow release nitrogen sources that have an extended nutrient release curve that prevents loss.

Mowing

During active summer growth, St. Augustinegrass should be mown roughly weekly. Like most turf species, the 1/3rd rule still applies. Never remove more than 1/3rd of above ground leaf length at any one time. If excessive clippings accumulate (a sure sign of over fertilization and/or poor mowing practices), then clipping removal is acceptable, but the preference is for clippings to be returned for proper nutrient cycling.

St. Augustinegrass recovers slowly from mower traffic, so avoid sharp turns and repetitive mowing patterns.

Insects

Chinch bugs are the most troublesome insect pests of St. Augustinegrass. In drier years, the southern chinch bug can be particularly problematic on St. Augustinegrass while not affecting other surrounding turf species. Floratam was selected for resistance (non-preference) to chinch bugs. But in most areas of our state, the poor winter survival of Floratam is consistently more problematic than chinch bug damage.

Scouting to correctly differentiate between insect damage and disease is critical. Insecticides will not control disease, and vice versa. One popular method to determine if insects are causing problems is the float test. Using a cylinder with both ends open, insert one end a few inches into the soil and fill it with water. If the area is affected by chinch bugs they will float to the top in about 10 mins time.

Controlling chinch bugs starts with proper thatch management. Chinch bugs make their homes in the thatch between soil and canopy level. Thatch can accumulate to excessive levels if mowing occurs infrequently or if too much fertility is applied at once. If thatch accumulation is greater than roughly an inch thick, then mechanical thatch removal by raking, light verticutting, or aerification may be warranted.

Many common lawn applied insecticides control chinch bugs. Examples include products containing clothianidin or any of the pyrethroid insecticides, such as bifenthrin, cyfluthrin, lambdacyhalothrin, or permethrin. (Fig. 2)

Disease

Large patch is a common disease of St. Augustinegrass lawns in our region and is caused by the fungus (Rhizoctonia solani). Large, circular patches with bright orange perimeters are especially evident during cooler spring and fall temperatures when the disease is active. Once summer temperatures arrive, the disease subsides and St. Augustinegrass slowly recovers. Preventing the disease through proper cultural practices is key. Disease severity is made worse by an overabundance of soil moisture during the spring and fall months. St. Augustinegrass is well adapted to medium and course textured soils, but poorly drained, heavier soils often lead to decline. This is most obvious in areas with standing/pooling water. Likewise, irrigating too much or too often may worsen the problem. Thatch accumulation is also a key contributing factor. (Fig. 3)

Certain fungicides may help alleviate symptoms of large patch. Products containing strobilurin or DMI fungicides are commonly applied during the fall, two to three weeks prior to disease outbreak, and repeated during early spring green-up (roughly 50% green leaves). Fungicide applications should be lightly watered into the upper most soil layer.

Take-all root rot (Gaeumannomyces graminis) is less common than large patch but is all the more troublesome. This is a root rot disease that is difficult to identify; therefore, a lab identification is often required. A key distinguishing factor when diagnosing take-all in the field is the ease with which grass stolons pull away from the soil. Maintaining relatively low soil pH (<6) is a standard recommendation, even though St. Augustinegrass thrives in soils around 6.5 to 7.5 pH. Acidifying fertilizers are recommended when take-all root rot has been diagnosed.

Strobilurin or DMI containing products can be used to reduce the spread of the root rot disease; however, they may not always be effective. These applications should occur during the spring when soil temperatures range between 65 and 70 degrees. They should be immediately watered into the root zone. If bare areas occur in the turf, topdress with a fine sphagnum peat moss to reduce soil pH and encourage regrowth into affected areas.

Gray leaf spot (Pyricularia grisea, or P. oryzae) is very common in the warm, humid southeast. It affects St. Augustinegrass during periods of prolonged wetness, especially during the warmer summer months. To prevent excess leaf moisture, late afternoon or evening irrigation should be avoided. Excess summer fertilization can also increase disease severity. When applied preventatively, strobilurin fungicides are effective at reducing gray leaf spot severity. (Fig. 4)

Weeds and herbicides

St. Augustinegrass can be injured by many common herbicides used on bermuda and zoysia grasses. Varietal differences are usually noted on label directions, along with use precautions about timing, appropriate temperature range, etc. Bottom line: no application is always safe. Avoid taking unnecessary risks. And always read and follow label directions.

Many preemergence herbicide labels limit use to areas of established turf only. Some restrict use on sod. (Fig. 5)

Preemergence herbicides that are labelled include (but are not limited to):

• Barricade 4FL and others (prodiamine)
• Bensumec 4LF (bensulide)
• Cavalcade 65 WDG (prodiamine, quinclorac)
• Dimension 2EW and others (dithiopyr)
• Gallery 75DF and others (isoxaben)
• Gemini 3.7 SC (prodiamine, isoxaben)
• Echelon (prodiamine, sulfentrazone)
• Freehand (dimethenamid, pendimethalin)
• Kerb SC T&O (pronamide)
• Pendulum AquaCap and others (pendimethalin)
• Pennant Magnum (S-metolachlor)
• Prograss (ethofumesate)
• Ronstar (oxadiazon) – Not labelled for residential use. Do not apply to St. Augustinegrass in California
• Specticle Flo (indaziflam)
• Surflan (oryzalin)
• Tower (dimethenamid)

Most postemergence herbicide labels thoroughly discuss use precautions in St. Augustinegrass or include application directions. But piecing together a narrative based upon common labels can be challenging, even for experts. For instance, Triplet-SF (containing 2,4-D, mecoprop, and dicamba) limits application timings to dormant St. Augustinegrass only. The analogous Trimec Classic product (also 2,4-D, mecoprop, and dicamba) says to avoid application during spring green-up and not to apply to ‘Floratam.’ (Fig. 6)

Regardless of labelling, a few precautions are worth noting. 1) St. Augustinegrass is extremely susceptible to injury during transition periods going into or coming out of winter. 2) High temperatures (~80°F or more) exacerbate injury, and low temperatures may prolong symptoms due to inability to recover. 3) Do not apply postemergence herbicides when grass is under stress from drought, temperature, insects, disease, or other herbicides. 4) Many herbicides caution against broadcast applications in order to reduce risks; alternatively, some caution against spot application, presumably due to the risk of splotchy lawns, or worse, dead spots.

Postemergence herbicides that are labelled include (but are not limited to):

• Aatrex (atrazine)
• Aethon (pyrimisulfan, penoxsulam)
• Asulam (asulox)
• Avenue South (penoxsulam, sulfentrazone, dicamba, 2,4-D)
• Banvel (dicamba)
• Basagran T&O (bentazon)
• Blindside (metsulfuron, sulfentrazone)
• Buctril 4EC (bromoxynil) – Do not apply to residential, playground, or schoolyard turf
• Coastal (prodiamine,
• simazine, imazaquin)
• Celero (imazosulfuron)
• Celsius WG (thiencarbazone, iodosulfuron, dicamba)
• Certainty (sulfosulfuron)
• Change-Up (MCPA, fluroxypyr, dicamba)
• Defendor (florasulam)
• Dismiss (sulfentrazone)
• Dismiss NXT (carfentrazone, sulfentrazone)
• Fahrenheit (dicamba, metsulfuron)
• Image (imazaquin)
• Lontrel (clopyralid) – Not labelled for residential use
• Manor, MSM-Turf, Rometsol, and others (metsulfuron)
• Manuscript (pinoxaden) – Sod only
• Octane 2SC (pyraflufen-ethyl)
• Princep Liquid (simazine)
• Quicksilver (carfentrazone)
• Relzar (halauxifen-methyl, florasulam)
• Sedgehammer, ProSedge, and others (halosulfuron)
• Speedzone Southern (carfentrazone, 2,4-D, mecoprop, dicamba)
• Switchblade (halauxifen-methyl, fluroxypyr, dicamba)
• Tenacity (mesotrione) – Sod only
• Triad Select (2,4-D, MCPA, dicamba) – Apply during dormancy only
• Trimec Classic (2,4-D, mecoprop, and dicamba) – Do not apply during spring transition or to ‘Flortam’
• Trimec Southern (MCPA, 2,4-D, dicamba)
• Triplet SF (2,4-D, mecoprop, dicamba) – apply during dormancy only
• Vista and/or Spotlight (fluroxypyr) – Do not apply to St. Augustinegrass in Florida
• Xonerate (amicarbazone)

Jay McCurdy is an Assistant Professor and Turfgrass Extension Specialist in the Department of Plant and Soil Sciences at Mississippi State University.

Maria Tomaso-Peterson is a Research Professor in the Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology at Mississippi State University.

Wayne Philley is a Research Associate and Turf Breeder in the Department of Plant and Soil Sciences at Mississippi State University.