Damn the Torpedograss!

Mike Bodle and Chuck Hanlon, South Florida Water Management District, 3301 Gun Club Rd., West Palm Beach, FL 33416 [email protected], [email protected]

Introduction Botanical description Torpedograss, native to Old World Torpedograss [Panicum repens (L.) Kissimmee Eurasia, is well established as one of Beauv.] is in the Poaceae family. Culms chain of lakes the world’s worst weeds (Holm et al., are rigid, 40-100 cm high, erect and/or Torpedograss is a serious prob- 1977, Panchal, 1981, Chandrasena and decumbent. Culms originate from lem in East Lake Tohopekaliga Dhammika, 1988). It was introduced sturdy, robust rhizomes which have shorelines, in the areas where th to the U.S. in the early 20 century many nodes. Bladeless overlapping cattle do not forage. In other either as an accidental ballast pollut- sheaths may wrap the culm base. areas, management by cattle is a ant or as a potential forage grass for Upper leaves are numerous with tremendous boon in Kissimmee the southeastern states (Tabor, 1952). loosely overlapping sheaths. Sheaths, chain of lakes. They feed on tor- Although cattle will use it as forage, it as a rule, are pilose along the margin, pedograss during winter low pool, is now considered invasive in Florida. but may be glabrous. The ciliate trun- when Bahia grass is senescent. In 1950, the University of Florida cated membranous ligule is approxi- Cattle have effectively managed warned, “Torpedograss is a serious mately 1 mm long. Blades are linear, torpedograss in many areas of the weed when established in farm and 4-15 cm long and 2-5 mm wide coming Kissimmee chain. grove land and indiscriminate plant- to a point. The leaf is stiff and rigid, flat Torpedograss is a recurrent ing without regard to future crops or or somewhat involute and spreading. problem during FWC lake restora- adjoining land is dangerous” (Hodges The upper surface is usually scantily tions involving extreme draw- and Jones, 1950). pilose but may be glabrous. The panicle downs and muck removal, as it is is open, approx- often among the first pioneers to imately 12 cm emerge when restoration work is long and can be done. During the 2000 drawdown terminal or axil- and restoration project of Lake lary. Spikelets Alligator, 80 acres of torpedograss are ovate, gla- required treatment. FWC staff brous and 2-5 expects serious problems during mm long (Hitch 2002 drawdown/restoration of cock and Chase, Lake Tohopekaliga. 1910). Seed pro- duction and viability is vari- able (Whyte et the top 60 cm of soil (Bor, 1960; Mani- al., 1968; Peng pura and Somaratne, 1974). Active and and Two, 1984; dormant axillary buds occur along the Wilcut et al. entire length of the rhizome (Chan- 1988a). drasena and Dhammika, 1988). Rhi- The rhizome zomes are noted for bulbil-like thicken- system is exten- ings, which contain abundant carbo- sive. Rhizomes hydrate reserves (Somaratne, 1952; are 3-5 mm in Manipura and Somaratne, 1974). Sub- diameter and 7 stantial carbohydrate reserves yield m or more in the capacity for rapid regeneration length, ending from axillary buds when rhizomes in a sharp, are fragmented or cut. (Chandrasena “torpedo-like” and Peiris, 1989). Rhizomes are the apex which can principal means of dissemination, easily penetrate method of persistence, and cause of soil. Rhizomes difficulty for control (Wilcut et al., can grow to a 1988b). depth of 7 m, however most Distribution and Habitat of the rhizomes Torpedograss occurs in 70% of Flor- are located in ida’s public waters (Schardt, 1994) and

6 FALL 2001 Dense torpedograss has overtaken many shallow areas of Lake Okeechobee’s western marsh where fragrant water lily formerly bloomed. Here the torpedograss nearly dwarfs SFWMD researchers. is naturalized in 57% of Florida’s 67 Economic counties (Wunderlin, 2000). uses The preferred habitat for torpedo- Torpedo- grass is a warm to hot climate with grass serves sandy soils, plentiful moisture, and as a soil sta- full sun (Holm et al., 1977). Sensitivity bilizer along to prolonged cold temperature limits ditchbanks, the spread of torpedograss in upper canals ,and latitudes or altitudes. In the tropics, rice paddies torpedograss is more commonly found during peri- in low coastal areas. Wilcut et al., (1988b) ods of high reported that exposing torpedograss water or rhizomes for 24 hours to 4.5 C was lethal heavy run- and concluded that, due to lack of cold off (Tarver, hardiness, torpedograss is restricted 1979; Pan- to regions with mild winters. In cool chal 1981). It has also been used as a stimulates new plant growth, which climates, torpedograss is less aggressive forage (Tarbor, 1952; Manipura and is often more susceptible to herbicide and is easily displaced by temperate Somartne, 1974; Siregar and Soemar- than unburned plants. Increased sus- species. woto, 1976). Tarver (1979) reported ceptibility may result from both better Torpedograss grows in many soil plantings of torpedograss throughout herbicide contact, as new torpedograss types from sandy, well-drained soils to southern Florida and in many counties growth is more exposed after burning heavy waterlogged soils. It grows best in North Florida . However, it was later has consumed previous mature tor- in soils that are poorly drained and have found that torpedograss did not have pedograss thatch, and herbicide effec- some degree of waterlogging (Holm, the nutritive qualities of other forage tiveness increases as more herbicide et al., 1977; Changrasena and Dham- grasses (Whyte. et al. 1959). penetrates through the immature cuti- mika, 1989a). Torpedograss is drought- cle of young shoots. resistant, and the rhizomes can survive Control Methods prolonged periods of water stress (Lubke Several herbicides, both alone and Current coverage et al., 1981). Interestingly, Wilcut et together with physical treatments in Lake Okeechobee al. (a988b) reported that air-drying including burning and disking (Smith, Torpedograss has displaced more torpedograss rhizomes to 35-60% of 1993), have been investigated. Also, than 16,000 acres of the 100,000 the original weight had no significant attempts have been made to control acres of native plant habitat in Lake effect on the regenerative capacity. This the plant with fungal innoculants Okeechobee’s marsh. Torpedograss has indicates that although torpedograss (Thayer, 1990). SFWMD research has demonstrated a wide range of tolerance grows best in a moist environment, it can shown that the best current control to moisture. It is capable of withstand- persist without water, adding further technology should combine fire with ing, and even growing, under flooded to its “weedy” characteristics. It thrives herbicide treatments. This combination conditions in the lake’s marsh. As a well in full sunlight, but can grow in yields the best and most-reproducible consequence, torpedograss persists at partial shade (Holm et al., 1977). results. Fire reduces plant biomass and virtually all stages in the lake.

8 FALL 2001 Resource Management Goal and Objectives for Lake Okeechobee The Goal of the torpedograss man- agement program is to protect the health and diversity of Lake Okeecho- bee’s natural plant and animal com- munities from the ecological degrada- tion caused by torpedograss.

Objectives Achieve an overall reduction of Prescribed burning consumes torpedograss so that Lake Okee- thick torpedograss mats and chobee’s native communities are no stimulates new growth. The longer dominated by torpedograss new growth is more susceptible and annual maintenance costs are to herbicide treatments. minimized. Implement an effective public infor- mation awareness program that will encourage support for torpedograss management.

Lake Okeechobee Torpedograss Management Efforts

Fire In the lake, prescribed fire is the most appropriate available physical

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WILDLAND WEEDS 9 Management recommendations for Lake Okeechobee Encourage continued funding for the continued treatment of dense and outlier populations of torpedograss in Lake Okeechobee Encourage torpedograss control programs for other publicly-owned natural areas in Florida. Continue funding of research program in the Lake to identify and optimize the most effect methods to control torpedograss. Transfer the results from continued torpedograss Above: Torpedograss covered this area of Lake control research to other natural areas in Florida. Okeechobee’s northwest marsh. After the entire area burned in early 2001, torpedograss has not yet regrown where Seek partnerships with concerned citizen groups to herbicides were applied after the fire (blackened area). support torpedograss management programs. Below: Five-acre torpedograss blocks were treated twice in Continue investigations into sound management four years. Several native plant species are colonizing these options. blocks. Use the support and resources of organizations such as the Florida Exotic Pest Plant Council to organize a network of professionals to lobby the State Legislature and U.S. Congress to support and enact laws encouraging the management of torpedograss and other exotic pest plants Cooperate with agencies and organizations such as Florida’s water management districts, the Florida Department of Environmental Protection, the IFAS cooperative extension service, and the Florida Native Plant Society in the production and dissemination of information intended to educate the public about the problems associated with nuisance exotic plants such as torpedograss.

method. Burning removes old tor- rapidly and vigorously and new its rhizomes are burned, which is pedograss thatch and stimulates new growth sprouts from previously dor- determined by depth of rhizomes and growth which is more susceptible to mant nodes. The use of prescribed fire depth of burning. In 1990, during a subsequent herbicide treatment. as a precursor to herbicide treatment, is prescribed fire and in a 1997 wildfire, SFWMD costs for prescribed burn- effective in breaking apical dominance water levels had receded below the ing have included staff time, helicopter and increasing herbicide efficacy. surface of the ground, with resultant time and other equipment and materi- Torpedograss grows in wet to moist torpedograss mortality. als. Staff support for fire management areas where its rhizomes are generally has also come from other Regional Fire protected from damage by fire when Herbicides Council member agencies. aerial portions burn. During extreme Herbicide treatments with ARSE- When fires occur in the areas cur- drought periods, water levels may NAL® herbicide have been adopted as rently infested by torpedograss in recede two to three feet below the sur- the most effective available treatment. Lake Okeechobee, water levels usually face of the ground. Fire then destroys Such treatments cost approximately remain no more than two or three not only the aerial vegetation but also $170 per acre, with 90% control last- inches below ground level. During the upper, dry, compacted peat layers ing, in some cases, up to one year. such water regimes, fire stimulates to a depth of three or four inches. Therefore, about $2.72 million would torpedograss growth. It recovers very Torpedograss is generally killed when be needed to treat 16,000 acres.

10 FALL 2001 Biological control continue as a funding source. Attempts to limit growth of tor- DuPuis Preserve pedograss in Florida by inoculation of Other potential sources Dupuis provides an excellent oppor- native fungi has shown little promise Preliminary discussions with staff tunity to conduct torpedograss studies except for populations growing under from the US Army Corps of Engineers on a smaller scale and in an area that is conditions of stress (Thayer, 1990). Aquatic Plant Control Operations readily accessible. Several large isolated To date, the United States Depart- Support Center do not hold promise wetlands are nearly 100% torpedograss. ment of Agriculture (USDA) has not for financial support. Their primary Qualitative observations at DuPuis Pre- conducted any torpedograss biocontrol program mandate is to maintain navi- serve have seemed to show competi- tion between maidencane (Panicum investigations. Grasses have tradition- gation and torpedograss infestations ally been considered “off limits” as hemitomon) and torpedograss. Maiden- do not typically threaten navigation. cane seems to act as a barrier to the biocontrol research targets, however, Funds may become available from spread of torpedograss. It is unknown more recent work has found potential Lake Okeechobee Protection Act and whether this barrier effect is reproduc- for selective biocontrol in the grass the Water Supply Contingency Plan ible, and if it is a result of physical, family. Great care must be exercised, programs. chemical or other function. However, it but grasses that occupy a unique habi- deserves further investigation. Studies tat, like lake margins, are more likely Research needs could include seeding or planting maid- than wider-ranging upland species to encane in conjunction with herbicide, fire or other management techniques. It have specific feeders. No funds are Seasonality of treatments currently available for such research is unlikely to be practical to attempt this Questions remain regarding on a large scale such as throughout the (Ted Center, personal comm). whether better control can be achieved Lake Okeechobee littoral zone. in particular season or time of the year. Funding To date, effectiveness of treatments has The DEP Bureau of Invasive Plant not shown a clear relationship with is ongoing to evaluate response of Management granted $309,000 to time of treatment during the year. torpedograss to different water levels. SFWMD for torpedograss manage- Initial findings include the potential ment in the lake (FY 2000). Both agen- Flooding responses for torpedograss expansion during cies aim to continue torpedograss Research contracted by SFWMD periods of low water levels. management with DEP grants likely to with the US Army Corps of Engineers

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WILDLAND WEEDS 11 Peng, S.Y. 1984. The biology and control of Wunderlin, R.P. and B.F. Hansen. 1996. Atlas of Literature Cited weeds in sugarcane. Dev. In Crop Sci. (4) Florida Vascular Plants, Institute for Systematic Center, Ted. Personal communication September, Essevier Sci., New York. P. 326. Botany, Univiversity of South Florida, Tampa. 2000. USDA Agricultural Research Station, Internet: www.plantatlas.usf.edu Davie, FL. Schardt, J.D. 1994. Florida Aquatic Plant Survey 1992. Tech. Report 942-CGA. Florida Dept. Chandrasena, J.P.N.R. 1990. Torpedograss of Environmental Protection, Tallahassee. (Panicum repens L.) control with lower rates 83pp. of glyphosate. Trop. Pest Man. 36:336-342. Kissimmee River Smith, B.E. 1993. Ecophysiological and techno- Chandrasena, J.P.N.R. and H.C.P. Peiris. 1989. logical factors that influence the management Studies on the biology of Panicum repens L. system of torpedograss [Panicum repens (L.) Beauv.]. II. Intraspecific competition and resource Torpedograss has not been a Master’s thesis, Department of Agronomy, allocation. Trop. Pest Man. 35:316-320. University of Florida. problem species on the Kissimmee Chandrasena, J.P.N.R. and W.H.T. Dhammika. River. Before re-flooding along Tabor, P. 1952. Comments on cogon and torpedo 1988. Studies on the biology of (Panicum grass: A challenge to weed workers. Weeds outer elevations of Rattlesnake Ham- repens L.) I. Comparative morphological 1:374-375. mock in Pool A, torpedograss was development of three selections from dif- ferenct geographical localities in Sri Lanka. Tarver, D.P. 1979. Torpedograss (Panicum repens initially dominant. It has subse- Trop. Pest Man. 34:291-297. L.). Aquatics 1:5-6. quently remained only as a compo- Hitchcock, A.S. and A. Chase. 1910. The North Thayer, P. and W.T. Haller. 1990. Fungal pathogens, nent of the wet prairie community. American species of Panicum. Washington Phoma and Fusarium, associated with declin- It has recently expanded in some Gov. Printing Office. Pp. 85-86. ing populations of torpedograss under high newly reflooded portions of the Pool water stress. Proc. European Weed Res. Soc. 8th Hodges, E.M. and D.W. Jones. 1950. Torpedo Symp. on Aquatic Weeds. Pp. 209-214. C floodplain. District researchers Grass. Circular S-14. Univ. of Fla. Ag. Experi- are not convinced it will become a mental Stations, Gainesville. 4 pp. Whyte, R.O., T.R.G. Moir and J.P. Cooper. 1968. Panicum repens L. Grasses in agriculture. nuisance requiring management. Holm, L.G. , D.L. Plucknett, J.V. Pancho and J.P. F.A.O., p. 352. Further, it may not necessarily exert Herberger. 1977. The World’s Worst Weeds. University Press, Hawaii. Wilcut, J.W., R.R. Dute, B. Truelove and D.E. negative impacts even if dominant Davis. 1988. Factors limiting the distribution Manipura, W.V. and A. Somartne. 1974. Some along the peripheral wet prairie. of cogongrass (Imperata cylindrica) and effects of manual and chemical defoliation Ongoing monitoring will reflect its torpedograss (Panicum repens). Weed Sci. on the growth and carbohydrate reserves of 36:49-55. coverage over time and some associ- (Panicum repens L.). Weed Res. 14:167-172. ated functional values including fish Wilcut, J.W., B. Truelove, D.E. Davis, and J.C. Panchal, Y.C. 1981. Control of Panicum repens Williams. 1988. Temperature factors limiting and wildlife habitat. L. in field channels. Proc. 8th Asian Pacific the spread of cogongrass (Imperata cylindrica) Weed Sci. Conf. Pp. 281-286. and torpedograss (Panicum repens).

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