Panicum mosaic virus (PMV) is a positive-sense single-stranded RNA viral pathogen that infects plant species in the panicoid tribe of the grass family, Poaceae.

The disease most commonly associated with the panicum mosaic virus pathogen is St. Augustine Decline Syndrome, which infects species of turf grass and causes chlorotic mottling.

[2] In addition to St. Augustine Decline, panicum mosaic virus is responsible for chlorotic streaking and mild green mosaicking in select cultivars of switchgrass and millet.

The strain specific to St. Augustine grass has since been observed in Arkansas, Louisiana, Mississippi and South Carolina in the United States, as well as in Mexico.

[7] The incubation period of panicum mosaic virus is fastest in warm conditions, around 29 to 35 degrees Celsius, and can take as few as 7–18 days.

[citation needed] Similar to its symptoms on millet and turf grass, panicum mosaic virus causes switchgrass to have chlorotic mottling and stunting.

As a result of the lack of resistance in cultivated species of switchgrass, there is a potential danger of developing large scale disease within energy cropping systems.

[14] Aside from resistance genes, another option of managing St. Augustine Decline Syndrome is cultural control by cleaning tools between mowing different properties to prevent the spread of pathogen.

[2] A third control option for St. Augustine Decline is to mow turf grass only during dry weather because the infected sap is not able to spread as easily.

[15] Despite the risks posed by cross-protection of crops using weak strains, the method has proven valuable in the control of several other viruses.