Torpedo grass, Panicum repens, is a hardy perennial grass occurring
widely throughout Florida but not native to North America. Shoots, up
to 1 m tall, arise from sturdy, creeping or floating rhizomes. The rhizomes are
pointed with torpedo-like growing tips. Aerial stems are rigid, erect to leaning,
with lower portions often wrapped in bladeless sheaths. The upper leaf
sheaths are mostly glabrous with hairs usually restricted to the upper margins. The ligule
(thin outgrowth at the junction of the leaf and leafstalk) is a short-ciliate
membrane. Leaf blades are narrow, linear, stiffly ascending to 25 cm long and
0.6 cm wide. The inflorescence is a loose open terminal panicle 7-22 cm long
with with few to many branches and stakled spikelets that are 2-3 mm long and
approximately 1 mm wide, with flower parts white with yellow. The small seeds are smooth
and whitish (Langeland and Burks 1998, CAIP, ISSG).
Potentially Misidentified Species
Several Panicum congeners similar in appearance occur in Florida.
Beachgrass (Panicum amarum), redtop panicum (P.
rigidulum), and maidencane (P.
hemitomon) all can be found within the IRL watershed counties). Details of the
rhizomes, leaves, and inflorescence must be studied to distinguish among
HABITAT AND DISTRIBUTION
Believed native to Europe or Australia Panicum repens is now widely
distributed throughout the tropics and subtropics from approximately 43° North
latitude to 35° South latitude (Holm et al. 1977).
In the U.S. southeast, the plant can be found from Florida to the Gulf coast of
Texas, and northward along the Atlantic Coast to North Carolina. The species
has also been introduced to California and Hawaii, where it has become a pest
plant to the sugarcane industry (Holm et al. 1977, Godfrey and Wooten 1979,
Small 1933, Langeland and Burks 1998). By 1995 P. repens was reported
as naturalized in 75% of Florida counties (Wunderlin and Hansen 2004). As of
April, 2007, the Florida Exotic Pest Plant Council (FLEPPC) reports the species
as present in 57 of 67 Florida counties.
Panicum repens occurs along the entire east coast of Florida, including the six IRL watershed
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Panicum repens is a perennial grass that grows to 1 m in height.
Panicum repens is a marginal species that occurs in and around shallow water.
It is found in more than 70% of Florida's public water bodies. The largest
Florida P. repens infestation, nearly 6,000 ha, is the infestation
occurring in and around Lake Okeechobee (Schardt 1994, Bodle and Hanlon 2001).
Panicum repens can reproduce sexually through flowering and seed production,
though the principal means of propagation is reported to be rhizome extension
and fragmentation (Holm et al. 1977).
Small P. repens fragments can give rise to dense clonal stands through
vegetative growth and rhizome fragments buried as deep as 50 cm can send up new
shoots (Hossain et al. 1999, Brecke et al. 2001). The lack of apical dominance
also allows each node the ability to produce axillary buds along entire rhizome
lengths (Wilcut et al. 1988). Hossain et al. (2001a) reports that a single culm
emerging from a single rhizome bud produced approximately 23,000 rhizome buds
in a single year.
Populations are capable of flowering and producing seeds year-round, but seed
abundance and viability are highly variable (Whyte et al. 1959, Peng and Twu
1979, Wilcut et al. 1988).
Torpedo grass distribution is restricted to the tropcs and subtropics. The
above-ground portions of the plant are easily killed by frost (FAO undated).
Panicum repens is most often encountered as riparian species in wetland and
marginal habitats, It grows well even after several days in standing water, but
is also drought-tolerant and can be found growing in heavy upland soils
(Sayer and Lavieren 1975, Holm et al. 1977, Langeland and Burks 1998). The
species is adapted to areas with significant seasonal rainfall and will not
survive extended hot dry seasons (FAO undated).
Panicum repens exhibits moderate salinity tolerance. It is reported to grow
on saline sands in western Zambia (Verboom & Brunt 1970).
Panicum repens tends to produce dense monocultures capable of displacing native vegetation.
The original native range of Panicum repens is in dispute. The type
specimen from which the species was first described by Linnaeus in 1762 was
collected from Spain, although several authorities suggest the native range of
the species to be Australia. The first description of this species (as P. airoides) from
Australia dates to 1810, therefore it is clear that the species has been
historically present in both locations.
P. repens was intentionally introduced to the southeastern United States
in the late 19th century as a cattle forage grass (Tarver 1979). It was
introduced to the Gulf Coast prior to 1876, at which time it was first
collected outside of cultivation near Mobile, Alabama (Beal 1896; Yarlett
1996). The plant was cultivated in Florida from at least the 1920s to the
1950s, becoming common in the state during this time and planted in most
southern Florida counties and also in some central and north-central counties
by 1950 (Hodges and Jones 1950).
Since this initial introduction P. repens has escaped cultivation to
spread into natural and agricultural lands in Alabama, Florida, Louisiana,
Mississippi, North Carolina, South Carolina, and Texas. The plant has also
been introduced to California and Hawaii (USDA, NRCS 2004).
Potential to Compete With Natives
The impressive vegetative reproductive capacity of Panicum repens allows it
to quickly produce dense monocultures capable of displacing native vegetation,
particularly in wetland and marginal habitats where the species thrives
(Shilling and Haller 1989, Bodle and Hanlon 2001).
Growth, vegetative reproduction, and spread of the species in agricultural
areas are facilitated by tilling and fertilization (Hodges and Jones 1950,
Possible Economic Consequences of Invasion
Sutton (1996) notes that worldwide Panicum repens is one of the most invasive
exotic grasses of terrestrial, wetland and aquatic habitats of the tropics and
subtropics. It is now listed as a Category I invasive species because of its
ability to invade and alter native plant communities (FLEPPC 2005).
In addition to overtaking natural areas, P. repens invades cultivated
lands and displaces more desirable forage species. Although it was originally
introduced for cattle forage, torpedograss becomes tough later in the growing
season and is generally neglected by livestock. Additionally, P. repens
may interfere with flood control, navigation, irrigation, recreation, and turf
production (Shilling and Haller 1989, Willard et al. 1998). This invasive
species has been a significant culprit in Florida citrus grove infestation and
has also been reported from parks, golf courses, and preserves throughout
Florida (Fleming et al. 1978, Baird et al. 1983, FLEPPC 1996).
Limited management of P. repens in Florida (e.g., management in flood
control systems) from 1980-1988 cost an average of $2-2.5 million per year
(Schmitz et al. 1988, Schardt and Schmitz 1991).
Baird D.D., Urrutia V.M. and D.P.H. Tucker. 1983. Management systems with
glyphosate on torpedograss in citrus. Proc. South. Weed Sci. Soc. 36:201-9.
Beal WJ. 1896. Grasses of North America. Volume. II. New York: H. Holt and Co.
Bodle M. and C. Hanlon. 2001. Damn the torpedograss! Wildland Weeds 4:6-12.
Brecke B.J., Unruh. J.B. and J.A. Dusky. 2001. Torpedograss (panicum
repens) control with Quinclorac in Bermudagrass (Cynodon dactylon x
C. transvaalensis) turf. Weed Technology Vol. 15:732-736.
FAO. Undated.Panicum repens L., species fact sheet. Available online
Fleming D.C., Palmertree H.D., and D.W. Houston. 1978. Screening herbicides for
torpedograss control in turf. Proceedings of the Southern Weed Science Society
FLEPPC. 1996. Florida Exotic Pest Plant Council occurrence database. Available
FLEPPC (Florida Exotic Pest Plant Council). 2003. Panicum repens.
FLEPPC. 2005. List of Florida's Invasive Species. Florida Exotic Pest Plant
Council. Available online.
Godfrey R.K. and J.W. Wooten. 1979. Aquatic and wetland plants of southeastern
United States, monocots. Athens (GA): University of Georgia Press. 712 p.
Hodges E.M. and D.W. Jones. 1950. Torpedo grass. Gainesville: University of
Florida, Institute of Food and Agricultural Sciences (IFAS). Ag. Experiment
Station Circular S 14. 4 p.
Holm L.G., Plucknett D.L., Pancho J.V. and J.P. Herberger. 1977. The world's
worst weeds: distribution and biology. Honolulu: University Press of Hawaii.
Hossain M. A., Kuramochi H., Ishimine Y., and H. Akamine. 2001a. Application
timing of asulam for torpedograss (Panicum repens L.) control in
sugarcane in Okinawa Island. Weed Biology and Management 1:108-114.
Hossain M.A., Akamine H., Nakamura I., Ishimine Y., and H. Kuramochi. 2001b.
Influence of temperature levels and planting time on the sprouting of
rhizome-bud and biomass production of torpedograss (Panicum repens L.)
in Okinawa Island, southern Japan. Weed Biology and Management 1:164-169.
Kretchman D.W. 1962. Torpedograss and Citrus Groves, Circular S-136. University
of Florida Cooperative Extension Service, Gainesville, Florida.
Langeland K.A. and K.C. Burks (Eds.). 1998. Identification and biology of
non-native plants in Florida's natural areas. UF/IFAS. 165 p.
Peng S.Y. and L.T. Twu. 1979. Studies on the regenerative capacity of rhizomes
of torpedo grass (Panicum repens Linn.), Part I, Characteristics in
sprouting of rhizomes and resistance to herbicides and environmental
adversities. Journal of the Agriculture Associatin of China 107:73-74.
Sayer J.A. and L.P. Van Lavieren. 1975. The ecology of the Kafue lechwe
population of Zambia before the operation of hydro-electric dams on the Kafue
River. East African Wildlife Journal 13: 9-37.
Schardt J.D. 1994. Florida Aquatic Plant Survey 1992. Florida Dept. of
Environmental Protection Technical Report number 942-CGA. 83 p.
Schardt J.D. and D.C. Schmitz. 1991. Florida aquatic plant survey 1990. Florida
Dept. of Natural Resources Technical Report number 91-CGA. 89 p.
Schmitz D.C., Nelson B.V., Nall L.E., and J.D. Schardt. 1988. Exotic aquatic
plants in Florida: A historical perspective and review of the present Aquatic
Plant Regulation Program. p 303-326 in: Proceedings of the Symposium on Exotic
Pest Plants, November 2-4, 1988, University of Miami, Miami, Florida. Technical
Small J.K. 1933. Manual of the southeastern flora, part one and two. Chapel
Hill NC: University of North Carolina Press. 1554 p.
Shilling D.G. and W.T. Haller. 1989. Interactive effects of diluent pH and
calcium content on glyphosate activity on Panicum repens L. (torpedo
grass). Weed Res. 29:441-448.
Sutton D. L. 1996. Growth of torpedograss from rhizomes planted under flooded
conditions. Journal of Aquatic Plant Management 34:50-53.
Tarver D.P. 1979. Torpedo grass (Panicum repens L.). Aquatics 1:5-6.
USDA, NRCS. 2004. The PLANTS Database, Version 3.5. National Plant Data Center,
Baton Rouge, LA 70874-4490 USA. Available online.
Verboom W.C. and M.A. Brunt. 1970. An ecological survey of Western Province,
Zambia, with special reference to the fodder resources. Vol. 2. The
grasslands and their development. Tolworth (Surrey), UK, Directorate of
Overseas Surveys. Land Resources Division Land Resource Study No. 8.
Whyte R.O., Moir T.R.G., and Cooper J.P. 1959. Panicum repens L. In:
Grasses in agriculture. FAO, Rome. 417 p.
Wilcut J.W., Dute R.R. Truelove B., and D.E. Davis . 1988. Factors limiting
the distributeon of cogon grass, Imperata cylindrical, and torpedo
grass, Panicum repens. Weed Science 36:577-582.
Willard T.R., Shilling D.G., Haller W.T., and K.A.. Langeland. 1998.
Physio-chemical factors influencing the control of torpedograss with
glyphosate. Journal of Aquatic Plant Management 36:11-15.
Wunderlin R.P. and B.F. Hansen. 2004. Atlas of Florida Vascular Plants.
Institute for Systematic Botany, University of South Florida, Tampa. Available
Yarlett L.L. 1996. Common Grasses of Florida and the Southeast. Florida Native
Plant Society. Spring Hill, Florida.