Virus-Resistant St. Augustinegrass

What Makes It Different

These are the two cultivars UF/IFAS Palm Beach County currently recommends for replacing a dead Floratam lawn — not because they shrug the virus off, but because they get infected like everything else and simply do not die of it.

The disease is sugarcane mosaic virus. In most grasses it causes mosaic — yellow streaking and mottling that looks bad and does no lasting harm. In Floratam alone it goes further, into lethal viral necrosis, killing the lawn within three years of infection and often faster; fresh Floratam sod laid into an affected area can be dead within months. Every other tested St. Augustine cultivar carries the virus without being killed by it, as do bermudagrass, bahiagrass and paspalum.

There is a hard irony in that. Floratam was released in the early 1970s partly for its resistance to St. Augustine Decline, the earlier virus that wrecked lawns along the Texas coast. Fifty years on, the cultivar bred to beat the first virus is the only one dying to the second.

Two things drive the spread. There is no cure — no fungicide, pesticide or vaccine touches a plant virus, so the only tools are resistant cultivars and sanitation. And St. Augustinegrass cannot be grown from seed, so a lawn is one cloned plant repeated across the whole yard: identical genome, identical vulnerability, nothing in it resistant. That is why a Floratam lawn goes all at once rather than thinning in patches.

The virus travels in the moist sap of freshly cut grass, carried on mower blades, decks and — the part most advice leaves out — wheels, and possibly line trimmers.

Who It’s For

Southeastern Florida first. Extension describes Palm Beach County as the most severely affected area in the state, in both ground covered and speed of spread, with losses running to many millions of dollars. It is also widespread in Pinellas County, where it appeared around 2011, and confirmed in a scattering of others.

Practically: a Floratam lawn showing yellow streaking or mottling that fertilizer and fungicide never fix, with patches that keep expanding. Symptoms are seasonal — summer heat and growth mask them, and they resurface as temperatures drop through late summer and winter, so a lawn that seemed to recover over summer probably did not. Outside the confirmed range this is not the axis to choose on; pick on cold, shade or drought instead.

The Cultivars

One name has come off the list. Bitterblue was previously counted among the virus-tolerant cultivars, but Palm Beach County extension no longer suggests it, citing uncertainty about how closely its genetic background resembles Floratam’s. If a supplier still offers it as the virus-safe option, that advice is out of date.

And if you are willing to leave St. Augustinegrass altogether, zoysiagrass is not a host at all — the one clean escape. Extension’s caution is that it needs noticeably more maintenance than Floratam in South Florida.

What Changes In Care

• Sanitation becomes a maintenance item. Mow only when the grass is dry, and mow your own lawn before anyone goes near an infected one. If you use a service, ask what they do between properties — the wheels carry sap as readily as the blade, so a wiped-down blade on a contaminated deck proves nothing.
• The mowing height drops if you are coming off Floratam. Palmetto wants about 2.5 inches in full sun and CitraBlue 2 to 3, against Floratam’s 3.5 to 4. Set the deck before the first cut, not after you have scalped it.
• Palmetto needs more fungicide attention than Floratam did. Large patch and take-all root rot are the two to watch, and the cool, wet shoulder seasons are when they show. Budget for a regular program rather than reacting to an outbreak.
• CitraBlue thatches. The dense horizontal growth that crowds out weeds is the same growth that builds thatch, so plan on annual core aeration from year two.
• Removal has to be complete, not spot. Extension notes spot removal may help very early, but a Floratam lawn usually needs replacing entirely, because the virus has almost certainly moved beyond the patches you can see. Half a lawn replaced is half a lawn reinfected.

If you are clearing the old lawn first, a non-selective herbicide with a 10 to 14 day wait before laying sod is the standard route. One label caution: consumer “Roundup” no longer reliably contains glyphosate, so read the active-ingredient panel rather than trusting the brand name.

Before You Buy

• Confirm the diagnosis before you spend a dollar. Yellowing in this grass has a long list of causes — chinch bugs, take-all root rot, large patch, iron chlorosis. Submit a sample for laboratory confirmation rather than replacing a lawn on appearance.
• Never resod an affected site with Floratam. Extension recorded Floratam sod laid to replace lawns lost in 2013 dying again in 2014, and fresh sod in affected areas dying within months. Price is not a reason to try it twice.
• Get the cultivar name in writing. Extension published guidance on visually identifying St. Augustinegrass cultivars because of this epidemic — buyers were being sold “St. Augustine” with no idea which one. Ask, and buy certified sod where you can.
• Do not buy Palmetto for the drought claim. It is widely advertised as drought-resistant; UF/IFAS says that is undocumented. Buy it for the virus resistance, the cold hardiness and the shade tolerance, which are real.
• Budget for the maintenance change, not just the pallet. With Palmetto that is a fungicide program; with CitraBlue the higher price and annual aeration. Uncertified “common” sod is the false economy here — weedy, not uniform, and unusually sensitive to 2,4-D. There is no St. Augustine seed, so anything sold as such is another grass.