Sugarcane Mosaic Virus is an emerging problem for our St. Augustine lawns in Florida. Viruses are some of the smallest and most simple pathogens. You need an electron microscope to see them. They are different from bacteria and fungi because they are not living organisms. They need a living host to replicate. But not all viruses cause disease. Some can replicate within a host without causing harm to the host. Some of our lovely variegated plants were created by introducing a virus into them.
Pathogenic viruses do cause disease and once a plant is infected not much can be done to get rid of it. Prevention is the best strategy which I will cover later in this article. The sugarcane mosaic virus does cause disease. And, unfortunately, Floratam which is the most popular cultivar of St. Augustine grass used in our area is most vulnerable to this virus.
Sugarcane mosaic virus has been around since before 2013 but its effects were mild. However, it is now spreading. The virus causes mosaic disease but because it is a virus it cannot be controlled by fungicides or other pesticides. The infection can cause severe damage to lawns and may kill the entire lawn as the grass declines. They refer to this as lethal viral necrosis (LVN).
The Floratam cultivar of St. Augustine is most vulnerable to progressing to LVN. Especially here in South Florida. The cultivars of Palmetto and CitraBlue are the most resistant to damage by the virus. Zoysia grass is not a host, for now. This virus also affects sugarcane (hence its name), bermudagrass, seashore paspalum, bahiagrass, and fountain grasses.
The most common symptom of mosaic disease is the mosaic pattern of damage on the leaf. There will be blotchy lines of yellow and light green on otherwise green grass blades. These streaks run along the veins. In the fall the lawn will show LVN and begin to turn brown and completely die. A lot of Marco Islanders came back to this unpleasant surprise as they returned for the season. This severe dieback really show up by spring.
Sugarcane Mosaic is mostly spread by infected lawn mowing equipment which brings clippings and sap from infected lawns to healthy, uninfected lawns. The University of Florida recommends cleaning all clippings and sap off of all equipment, especially mowers, trimmers and shoes and then sterilize by spraying with a bleach, alcohol or quaternary ammonia solution. While a homeowner mowing his own lawn may be able to do this with every mowing it is not a practical solution for the professional lawn care companies who mow dozens of lawns a day.
This suggestion takes me back to our problem of the spreading of ganoderma infection of our palm trees. The prevention solution was also to clean and disinfect chain saws and other pruning tools between jobs. Once again it was not feasible for a landscape company to completely clean the equipment of all microscopic debris between jobs. My suggestion was to have a “dirty” saw used only on known diseased trees keeping your other tools disease free. While not an ideal solution I felt it was better than nothing. So if a landscaper knows that he has a lawn infected with mosaic disease perhaps he could have another “dirty” push mower or line trimmer used exclusively on diseased areas. This of course would mean you would have to know you have mosaic disease in the first place.
This virus can also be spread by aphids and I would think chinch bugs along with infected sod. It should be noted that it has not been found on any sod farms, yet. It would be best to inspect any new sod before introducing it to your yard.
If you suspect you have a mosaic disease you should submit a sample of your grass for testing to UF/IFAS Plant Diagnostic Center.
And finally as I always say a healthy lawn or plant is able to resist disease better than an unhealthy one. So use good horticultural practices to keep your lawn healthy.
- Mow at the proper height for your grass type. Augustine’s optimum height is 3 ½” to 4”. I still see a lot of lawns being cut too short which will weaken them and make them more susceptible to diseases like mosaic. And don’t mow your lawn when it is wet since this can help move pathogens throughout the lawn. Keep your mower blades sharp for a clean cut that will heal quickly and prevent openings for pathogens to enter the grass blade.
- Fertilize correctly. Rates and timing are important. Refer to EDIS Publication EP221 – General Recommendations for Fertilization of Turfgrasses on Florida Soils. Some of the local fertilizer ordinances have rules that are more harmful than helpful to a healthy trufgrass so follow the scientific guidelines.
- Irrigation – Apply ½” to ¾” per session. Our sandy soil would prefer the ¾” amount. Put out some tuna cans, run your sprinklers and measure to see how long they need to run to achieve the ¾” application. In spring, summer and fall once or twice a week is recommended. But with cooler winter weather once a week or even once every other week is enough. And water in the early morning so the leaf blades dry when the sun comes out. Never water in the late afternoon or evening as this leaves the blades wet into the night and increases the chance of disease.
Follow the above recommendations to keep your lawn healthy because prevention is the best, and possibly the only strategy, against the Sugarcane Mosaic Virus.