Torpedo grass gets its name from the shape of its leaves and the way it spreads aggressively. The leaves are long, thin, and pointed, resembling the shape of an old naval torpedo. This invasive grass also “torpedoes” across lawns and fields, shooting up new plants from underground stems and roots. Once established, torpedo grass is very difficult to control, much like a fast moving torpedo that is hard to stop.
What is torpedo grass?
Torpedo grass (Panicum repens) is a warm season perennial grass that is considered an aggressive lawn, pasture, and turfgrass weed. It is also classified as an invasive species in many areas. This undesirable grass is adapted to warm, humid climates and is found throughout most of the southeastern United States and tropical regions worldwide.
Torpedo grass is a creeping grass that spreads by above-ground runners or stolons, as well as by an extensive system of underground stems called rhizomes. These creeping stems allow torpedo grass to form new plants away from the original plant. The upright flower stems grow 1-3 feet tall and bear narrow, erect, green to purple flower spikelets.
The thin, pointed leaf blades are 1-6 inches long and up to 1/4 inches wide. They are smooth or slightly hairy and have a light green color. The ligule (junction of leaf blade and leaf sheath) is a fringe of hairs. Leaves are arranged alternately along the slender stems.
Why is it called torpedo grass?
There are a few key reasons why this invasive grass is called torpedo grass:
- The long, pointed leaf shape resembles the shape of naval torpedoes used in the early 1900s when the grass arrived in the United States.
- It spreads aggressively through lawns and fields like a torpedo speeding through water.
- The underground rhizomes radiate out from the original plant like torpedoes launching from a ship.
- Trying to remove torpedo grass can feel like trying to stop an incoming torpedo – difficult to stop the steady advance.
In summary, the name refers to both the leaf shape and invasive growth habit of this stubborn grass.
Where did torpedo grass originate?
Torpedo grass is native to Africa, Southeast Asia, and southern Europe. It arrived in the southern United States in the early 1900s as a forage crop and ground cover. Since that time, it has naturalized and become an invasive species in the southeastern U.S. from Texas to Florida and as far north as Virginia.
It was likely introduced accidentally as a contaminant in cultivated grass seed. Today, it continues to spread to new areas as a weed hitchhiking on equipment, vehicles, animals, clothing, and other means.
What are the growth habits of torpedo grass?
Torpedo grass grows aggressively under warm, humid conditions. Growth occurs during the summer and declines in winter. It tolerates hot, dry conditions better than many grasses once established. Some key growth habits include:
- Rhizomes & stolons – Spreads rapidly by thick, scaly rhizomes under the soil surface and by above-ground stolons or runners. Rhizomes may grow 6 feet deep.
- Seed production – Produces viable seed but main reproduction is vegetative through rhizomes. Doesn’t need seed to spread.
- Establishment – Rhizome fragments as small as 2 inches can take root and establish new plants.
- Colonization – Can quickly colonize and form dense mats, displacing other grasses.
- Aggressive growth – Quickly invades lawns, roadsides, pastures, and natural areas. Hard to stop spread.
These vigorous growth habits allow torpedo grass to spread quickly and outcompete other plants once established. It forms thick mats of grass that are difficult to control.
Where does torpedo grass grow?
Some of the main habitats for torpedo grass growth include:
- Lawns – Invades home lawns, golf courses, sports fields, cemeteries
- Roadsides – Common on road shoulders, medians, drainages
- Pastures – Overtakes grazing areas and reduces forage production
- Waterways – Common on banks of ponds, lakes, rivers, canals
- Coastal areas – Invades coastal habitats like dunes, marshes, mangroves
- Agricultural land – Spreads into cropland, orchards, vineyards
- Disturbed sites – Thrives on disturbed soils and abandoned land
Torpedo grass tolerates partial shade but does best in full sun. It requires moist soils and does not grow well on dry, upland sites. Fertile, moist soils promote the most aggressive growth.
How does torpedo grass spread?
Torpedo grass utilizes several effective methods to spread rapidly once established:
- Rhizomes – Underground rhizomes sprout new plants away from original plant. Rhizomes may grow 6 feet deep.
- Stolons – Above-ground runners or stolons root at nodes to form new plants.
- Root fragments – Pieces of roots and rhizomes break off and are spread by soil movement, vehicles, etc.
- Mechanical transfer – Spreads by mowers, tractor implements, etc. that move fragments.
- Water dispersal – Rhizomes float and spread along waterways via currents and floods.
- Animals/people – Transported by movement of animals, clothing, shoes, gear.
Managing the spread relies on early detection and treatment of new colonies. Once established, containment and control become much more difficult.
Why is torpedo grass problematic?
Torpedo grass earns its status as a highly invasive weed for these reasons:
- Forms dense colonies and mats that crowd out desirable grasses
- Reduce yields in pastures and agricultural fields
- Very tough to control once established; rhizomes resist most treatments
- Regenerates from tiny rhizome and root fragments
- Rhizome mats prevent seed germination of other plants
- Stolons and flower stems inhibit mowing and mechanical control
- Unchecked growth leads to monocultures and loss of plant diversity
The combination of aggressive, hardy growth and multiple reproductive strategies make torpedo grass a formidable invasive species across the southern U.S. Regions where it is not yet widespread have implemented quarantines and restrictions to try preventing its introduction and spread.
How does torpedo grass impact crops?
Torpedo grass causes significant reductions in crop yield and quality when it invades agricultural fields, including:
- Row crops – Corn, soybeans, cotton, etc. see up to 50% yield declines.
- Orchards & vineyards – Tree and vine growth stunted; fruit yield reduced.
- Pastures – Forage production cut by 35-45%; cattle avoid eating.
- Turf farms – Sod quality severely reduced by invasion.
- Irrigation issues – Rhizome mats block irrigation pipes and damage systems.
Prevention of invasion is critical to avoid torpedo grass impacts on crops. Infested fields require intensive management to control existing plants and prevent further spread.
How is torpedo grass controlled and managed?
Effective integrated management of torpedo grass involves preventive and control measures:
- Cultural methods – Promote healthy, dense turf and pastures that resist invasion. Avoid overwatering.
- Mechanical removal – Repeated tilling uproots plants but must remove all rhizomes.
- Cutting/mowing – Frequent, low mowing helps suppress growth but does not kill plants.
- Herbicides – Systemic herbicides most effective. Glyphosate provides suppression but not eradication.
- Repeat treatments – Control requires repeated, integrated efforts over a long time.
- Replanting – Establish new desirable vegetation to prevent reinvasion.
Torpedo grass exhausts resources of invaded plants making the areas more susceptible to reinvasion. Thus ongoing monitoring and maintenance are required after initial control.
Can animals graze on torpedo grass?
Torpedo grass has very low palatability and grazing value for livestock such as cattle. Animals will avoid grazing on torpedo grass if other forages are available. Reasons include:
- Low protein content provides poor nutritional value
- Undesirable taste deters grazing
- Erect flower stems are abrasive on mouths
- Dense mats inhibit access by grazing animals
- Studies show cattle weight gain is very poor on torpedo grass pastures
Some animals like goats will eat torpedo grass when more desirable forages are unavailable. But it provides very limited nutritional value and animals will lose weight forced to eat it.
Does torpedo grass have any uses?
Despite being considered a major pest plant, torpedo grass does have some limited uses, including:
- Forage – Provides very low quality grazing when other forage unavailable.
- Erosion control – Dense root mats help stabilize soil against erosion.
- Biofuel – High productivity makes it a potential bioenergy crop.
- Thatching – Used for thatching material in Africa.
- Cellulose source – Fibers used for paper, fiberboard production.
However, the highly invasive tendencies generally outweigh these potential benefits. More research is needed to utilize torpedo grass as a productive crop rather than a problematic weed.
| Use | Description |
|---|---|
| Forage | Very low quality grazing for livestock when other forage is limited |
| Erosion control | Rhizome mats stabilize soil against erosion |
| Biofuel | High productivity makes it a potential bioenergy crop |
| Thatching | Used for thatching material in parts of Africa |
| Cellulose source | Fibers used for paper, fiberboard production |
Key facts about torpedo grass
- Native to Africa, southern Europe, Southeast Asia
- Introduced to southern U.S. in early 1900s as forage crop
- Considered a highly invasive weed across southern regions
- Reproduces by seeds, rhizomes, and above-ground stolons
- Long, pointed leaf shape resembles torpedo shape
- Spreads rapidly like a launched torpedo
- Displaces desirable grasses in lawns, pastures, and crops
- Reduces yields of crops and forage quality
- Difficult to control due to deep, extensive rhizome system
- No biological control agents available yet
These key facts highlight why torpedo grass is considered such a problematic invasive plant across the regions where it has spread.
Conclusion
Torpedo grass is an invasive weed perfectly named for its distinctive leaf shape and aggressive growth habit. The pointed leaves resemble the form of torpedoes, while the rapid spread across lawns and fields is similar to a torpedo speeding through water. This grass arrived in the southern U.S. in the early 1900s and soon displayed its invasive tendencies. While it has some limited uses, torpedo grass causes major reductions in crop yields, forage production, and turf quality wherever it infests. Managing torpedo grass requires diligent effort combining cultural, mechanical, chemical, and biological controls.