Jeffrey Beasley, Strahan, Ronald E., Voitier, Matthew, Sanders, Kayla
Torpedograss (Panicum repens L.) is a warm-season, perennial grassy weed common throughout Louisiana. It spreads primarily through creeping rhizomes (underground stems). Torpedograss prefers wet soils and is typically found growing in shallow water. It can tolerate mowing but if left unmanaged can grow up to 3 feet in height. Torpedograss is very aggressive, making it a difficult weed to control in turfgrass.
Torpedograss has waxy silver-green leaves that are pointed at the tip. Leaves can be flat or folded and hair is typically present on the surface and around the sheath. Both leaves and stems are stiff and erect. Seed heads are small and flat and are white to brown in color. Torpedograss produces stolons (aboveground stems) and robust rhizomes (underground stems), which are sharply pointed at the tip, resembling a torpedo. Rhizomes aggressively creep through the soil and allow the weed to spread rapidly. For more information on torpedograss identification and characterization, visit the USDA Plants Database at https://plants.usda.gov.
The best way to prevent or reduce weed encroachment is to maintain a healthy lawn through proper fertilization and soil pH and regular mowing. Properly maintaining a lawn through these cultural practices promotes dense and vigorous turfgrass, allowing it to better compete with weeds. Below are the recommended mowing heights and nitrogen fertility rates recommended per turfgrass species. Prevention is the most important method for managing torpedograss. Torpedograss is often introduced into landscapes from contaminated soils used for flower bed and lawn renovation or construction. Make sure soils brought in from other sites are free from torpedograss.
In addition to cultural practices, herbicide applications may be required to achieve effective weed control. However, once torpedograss becomes established in the lawn, selectively removing the weed can be very difficult. Repeated use of the post-emergence herbicide quinclorac can be useful in managing torpedograss in bermudagrass and zoysia lawns. There are no selective herbicide options for St. Augustine grass. Sethoxydim only temporarily suppresses torpedograss in centipedegrass.
Spot applications of a non-selective herbicide, such as glyphosate, will kill torpedograss, but turfgrass in these treated areas will need to be re-established by resodding or seeding damaged areas.
When applying any type of herbicide, you must follow the manufacturer's labeled directions. For more information regarding pesticides for turfgrass, please reference the Louisiana Suggested Chemical Weed Control Guide at the LSU AgCenter website www.lsuagcenter.com.