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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
species.
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
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.
IRL Distribution:
Panicum repens occurs along the entire east coast of Florida, including the six IRL watershed
counties.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Panicum repens is a perennial grass that grows to 1 m in height.
Abundance:
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).
Reproduction:
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.
Embryology:
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).
IV. PHYSICAL TOLERANCES
Temperature:
Torpedo grass distribution is restricted to the tropcs and subtropics. The
above-ground portions of the plant are easily killed by frost (FAO undated).
Hydrology:
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).
Salinity:
Panicum repens exhibits moderate salinity tolerance. It is reported to grow
on saline sands in western Zambia (Verboom & Brunt 1970).
V. COMMUNITY ECOLOGY
Trophic Mode:
Autotrophic (photosynthetic).
Associated Species:
Panicum repens tends to produce dense monocultures capable of displacing native vegetation.
VI. INVASION INFORMATION
Invasion History:
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,
FLEPPC 2003).
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).
VII.
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675 p.
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repens) control with Quinclorac in Bermudagrass (Cynodon dactylon x
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of Florida Cooperative Extension Service, Gainesville, Florida.
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Shilling D.G. and W.T. Haller. 1989. Interactive effects of diluent pH and
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Plant Society. Spring Hill, Florida.
Report by:
J. Masterson, Smithsonian Marine Station
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