FR342 Biology and Control of Cogongrass (Imperata cylindrica) in Southern Forests1 Patrick J. Minogue, Brent V. Brodbeck, and James H. Miller2 Cogongrass Biology Control of cogongrass is difficult because it spreads in two ways: by extensive rhizome systems and by seeds (Holm et Cogongrass (Imperata cylindrica (L.) Beauv.) is a warm- al. 1977, Brook 1989). Cogongrass rhizomes can comprise season perennial grass species found throughout tropical more than 60% of the total plant biomass. The rhizomes and sub-tropical regions of the world (Hubbard 1944). support rapid re-growth following mowing or burning Native to Southeast Asia, cogongrass is an aggressive (Sajise 1976). The fibrous root system grows from nodes on invasive plant that that has spread to all continents except branched rhizomes that form a dense mat able to exclude Antarctica (MacDonald 2004) and is considered among most other vegetation (Ayeni 1985), and may contribute the worst problematic weeds on a global scale (Holm et to rapid re-growth following cutting, disking, or burning al. 1977). In the United States, it is naturalized in Virginia, (Sajise 1976, Ramsey et al. 2003). Rhizomes are tough and North Carolina, South Carolina, Georgia, Florida, Alabama, white and are covered with light brown colored cataphylls Mississippi, Louisiana, Texas, and Oregon (USDA Plants (scale leaves), which form a protective sheath. They have 2017). It was first accidentally introduced in the United short internodes and sharp root caps (Ayeni 1985). The States near Mobile Alabama in 1912 (Tabor 1949 and 1952, aboveground plant has no stems, although individual leaves Dickens 1974) and subsequently intentionally introduced may reach nearly 5 feet in length (Holm et al. 1977, Bryson from the Philippines into Mississippi as a forage crop in and Carter 1993). Leaves exhibit a distinct lime green color 1921 (Tabor 1949 and 1952, Patterson et al. 1979, Tanner and are slender, flat, and linear-lanceolate with serrated leaf and Werner 1986). Plants from Mississippi were replanted margins and a prominent, typically off-center white mid-rib in Florida for forage and soil stabilization in the 1930s (Hubbard 1944, Holm et al. 1977). (Tabor 1949, Hall 1983, USDA NISIC 2017), though its high silica and low protein content made cogongrass an The importance of seeds in the spread of cogongrass in the inadequate forage crop (Coile and Shilling 1993, Garrity et southeastern United States is less clearly established than al. 1993). These early regional introductions contributed to the importance of roots (Dozier et al. 1998, Willard et al. the establishment of cogongrass in the Southeast. Points of 1990, MacDonald 2007, Ludovic et al. 2008). Cogongrass introduction, including forage trials, are often areas where produces prolific seeds (c 3,000 per plant) from compacted, cogongrass remains most well established (Willard et al. cylindrical, shortly branched, spike-like, fluffy, white 1990). Cogongrass is regulated as a federal noxious weed plumes 4 to 8 inches long. Seeds can travel long distances (USDA Plants 2017). 1. This document is FR342, one of a series of the School of Forest Resources and Conservation, UF/IFAS Extension. Original publication date March 2018. Visit the EDIS website at http://edis.ifas.ufl.edu. 2. Patrick J. Minogue, associate professor; Brent Brodbeck, senior biological scientist, School of Forest Resources and Conservation, UF/IFAS North Florida Research and Education Center; and James H. Miller, emeritus scientist, USDA Forest Service, George Andrews Laboratory; UF/IFAS Extension, Gainesville, FL 32611. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension. (Hubbard 1944, McDonald et al. 1996), but generally seed 1995, Ramsey et al. 2003); fast-growing legumes such as movement averages 16 ft (Holm et al. 1977, McDonald et velvetbean have been used successfully in other countries al. 1996). Although seeds are potentially highly germinable (Chikoye et al. 2002). (more than 90% of the seeds will sprout), low spikelet fill often results in much lower germination rates (Schilling et Mechanical control alone has been shown to be ineffective al. 1997, Dozier et al. 1998, Burnell et al. 2003). There may once cogongrass is established. Burning of cogongrass be regional differences in seed viability. Viable seeds have produces unusually hot fires because of the fuel charac- been reported in Florida, Mississippi, and Alabama, but teristics of the aboveground biomass. The sandhills of large areas of cogongrass infestation in central Florida do the southeastern United States support a pyrogenic pine not produce fertile seed (MacDonald 2007). Cogongrass savanna ecosystem sustained by relatively frequent low- is an obligate outcrossing species; therefore, populations intensity fires fueled by native grasses and pine needle-fall. arising from rhizomes persist vegetatively until they grow Lippincott (2000) found that cogongrass invasions into this in close proximity to genetically different populations and ecosystem significantly increase fine fuel loads, resulting in produce viable seed (McDonald et al. 1996, Dozier et al. fires that are more horizontally contiguous and have greater 1998, MacDonald 2007). Seeds have no dormancy, and seed fire heights and higher maximum temperatures. These viability declines rapidly, with a complete loss in viability cogongrass-fueled fires kill juvenile longleaf pine (Pinus after one year (Schilling et al. 1997, Dozier et al. 1998). palustris Mill.). The cogongrass rhizome system is able to Patterns of molecular analyses of stands of cogongrass in persist following fire, whereas many other types of vegeta- different locals suggests that successful long-range dispersal tion do not (Eussen and Wirjahardja 1973; Seavoy 1975). may be due to human activity rather than typical wind Cogongrass patches have been shown to be more numerous dispersal of seeds (Ludovic et al. 2008). and larger in recently burned plots (Holzmueller and Jose 2012). Mowing can temporarily inhibit and remove cogongrass biomass above the ground, but mowing does Control of Cogongrass not suppress cogongrass long-term (Willard et al. 1996). Although cogongrass has many natural pests, including Repeated disking and deep plowing have been shown more than 80 pathogens, 90 insects, and several nematodes to be effective in suppressing or eradicating cogongrass and mites reported worldwide (Van Loan et al. 2002), in intensive agricultural settings, but these practices are in biological control studies insects and fungi have been impractical in many habitats such as forests or natural plant shown to be generally ineffective (Ivens 1980, Brook 1989, communities (MacDonald 2004). MacDonald 2007). Recently, surveys in Asia an East Africa for potential biological control agents, identified several In forests, the only effective method for suppression insect herbivores , including several genera of stem borers or elimination of existing patches of cogongrass is and gall-forming midges, that show some promise. Based chemical control. A body of research in the southeastern on life histories and field collection data, it appears these United States has identified glyphosate, imazapyr, and genera may have restricted host ranges (Overholt et al. combinations of these herbicides as effective in managing 2016). cogongrass, although complete control is achieved only with repeated applications (Willard et al. 1996 and 1997, Establishment of competing vegetation has been more suc- Shilling et al. 1997, Dozier et al. 1998, Johnson 1999, cessful in controlling the spread of cogongrass. Bahiagrass Ramsey et al. 2003). Both glyphosate and imazapyr are (Paspalum notatum Fluegge) sod cover has been effective readily absorbed and translocated to rhizomes (Townson in managing cogongrass infestations in the southeastern and Butler 1990). Used alone, imazapyr is more effective United States (Shilling et al. 1997, Willard and Shilling than glyphosate (Willard et al. 1996, Dozier et al. 1998, 1990). Common hulled bermudagrass (Cynodou doctylon Ramsey et al. 2003), but imazapyr is a broad-spectrum, (L.) Pers.) and hairy indigo (Idigofera hirsuta Harvey) have persistent, soil-active herbicide that often causes damage also inhibited cogongrass establishment (Gaffney 1996), but to non-target vegetation, particularly hardwood trees and bahiagrass, bermudagrass, and hairy indigo are non-native shrubs. Cogongrass control is most effective at the higher and are also potentially invasive in forests and natural areas. labeled rates of glyphosate or imazapyr, and the most effec- In Indonesia, establishment of forests with understory cover tive time of application is in late summer or fall (Shilling et crops has been effective in suppressing, but not eradicating, al. 1997, Willard et al. 1997, Ramsey et al. 2003). Combina- cogongrass (Macdicken