Lethal Viral Necrosis (LVN), caused by Sugarcane Mosaic Virus, kills Floratam lawns within three years of infection. Floratam, by far is the most popular cultivar of St. Augustinegrass used in Florida. Cooler late summer/fall and winter temperatures usually make mosaic virus symptoms more apparent.
Floratam has been one of the better St. Augustinegrass cultivars for Florida since the 1970’s because of its relative resistance to fungal diseases, and another viral disease that devastated other St. Augustinegrass cultivars along the Texas coastline. Lethal Viral Necrosis was initially thought to be caused by two combined viruses, but UF research recently demonstrated that only one virus, Sugarcane Mosaic Virus, is the culprit. We first identified the disease in Palm Beach County, Florida in 2013. It was previously identified in Pinellas County, Florida around 2011. Several other counties now have a few laboratory documented instances of the disease, although Palm Beach County appears to be the most severely affected area within Florida in terms of area affected and rapidness of spread, with many millions of dollars in losses so far.
The mosaic virus also infects, but does not kill other tested St. Augustinegrass cultivars. Additionally, other types of turfgrass like Bermudagrass, bahiagrass and paspalum are not killed. “Mosaic” is a term used in those grasses when yellow, but not necrotic spotting symptoms are mildly visible. Zoysiagrass also is not affected at all, but tends to require much higher levels of maintenance in Palm Beach County than does Floratam. Therefore, it may not be an appropriate residential lawn replacement.
The virus is spread in the moist sap from freshly cut lawns on the wheels of mowers, blades, mower decks, and possibly line trimmers. The wheels are important in the transmission as they help “grind” and therefore inoculate the virus into leaves. Aphids might also be incidental, but minor spreaders of the virus. Potentially, new sod could be a source, but no submitted specimens to UF labs from sod farms have yet tested positive. As lawns decline from the disease, weeds become much more of a problem. If a relatively new heavy weed infestation is noticed, check for the possibility of LVN by looking more closely for symptoms on grass blades as seen in the photo above. Also, heavily affected lawns may have a slight “bronzish” tinge which is noticeable by some people, but is difficult to capture in a photo. Lawn disease managers experienced with LVN can often spot affected lawns even when just driving by.
What Can You Do?
Fungicides and other pesticides are ineffective against this mosaic virus. No vaccine exists, or is likely to ever be developed. Cultural practices like fertilization or watering will not save an infected Floratam lawn, but UF St. Augustinegrass best management practices are still recommended.
Sanitation methods have had limited effectiveness in slowing the spread of the disease in Palm Beach County. Nevertheless, current recommendations after mowing infected lawns are to blow grass debris off equipment and wheels, and then spray equipment until wet with a disinfectant. Allow disinfectant to dry completely before using equipment on other lawns. The two most effective disinfectants are:
- 2% solution of DuPont Virkon S disinfectant
- 9 parts water to 1 part Household Bleach solution (5.25% sodium hypochlorite) Warning: bleach causes steel to rust
Also, when possible, avoid mowing wet lawns. Clippings left on infected lawns will not increase the spread of mosaic, nor will the use of reclaimed irrigation water. The virus will not typically be spread by walking, or dragging hoses across lawns. Also, once the virus containing plant sap dries, the virus will no longer be spread on surfaces.
The primary management strategy in Palm Beach County is to replace dead or dying Floratam St. Augustinegrass with another turfgrass cultivar or selection. Palmetto currently is the best St. Augustinegrass cultivar replacement for southeastern Florida, but tends to have greater large patch and take-all root rot fungal issues than does Floratam. CitraBlue is another UF introduction in the final stages of evaluation, but it is not yet ready to be recommended as resistant to LVN. However, the first two years of field trials have been very promising. Communities may wish to replace dying Floratam with CitraBlue in small trials to become familiar with it by the time commercially available quantities become more abundant in the next year. Bitterblue is a very old cultivar and is no longer recommended due to its uncertain cultivar genetic makeup, which may include Floratam. When replacing LVN affected Floratam lawns, first kill the still living remnants with an appropriate herbicide, and rake up debris before replanting. Alternatively, infected Floratam lawns can be peeled up with a sod cutter, or similar methods before replanting. The goal is to improve contact with the soil of any newly planted sod for better transplanting success. The virus cannot be spread through soil. However, spread by any means becomes a moot issue if resistant cultivars are the replacement choice. Floratam cultivar may still be an acceptable selection in areas of the state where LVN has not occurred.
For more information, visit:
LVN Webpage or
Photo: UF/IFAS Schall
Updated January 21, 2021