827 Imperata cylindricaCommon Names: Japanese blood grass, cogongrass, satintail, blady grass, cranberry grass, kunai Family: Poaceae (grass Family)
Cogongrass is a bright chartreusey green perennial grass that grows 2-4 ft (0.6-1.2 m) tall and forms dense stands, to the exclusion of other plant species. The erect leaf blades are about 0.5 in (1.3 cm) wide and have a prominent whitish off-center midrib and a sharp tip. The leaves are flat and have saw-like edges lined with sharp microscopic silica crystals. The round leaf bases are sheathed and attached to short round stems. The upper part of the leaf blade is hairy near the base, but the underside is smooth. As the plants go dormant, the leaves turn brownish-gray from the tips downward. The dead leaves remain standing and resist decay. Cogongrass roots are sharp pointed white barbwire-like rhizomes that branch readily and rapidly shoot out from one plant to form another, sometimes going right through the roots of intervening plants. Most of these rhizomes are interwoven in a dense mat within about a foot of the soil surface, but some may reach as deep as 3-6 ft (0.9-1.8 m). Cogongrass flowers are borne in conspicuous cylindrical silky white spikes 1-16 in (2.5-40.6 cm) long and 0.25-1 in (0.6-2.5 cm)in diameter. Each individual flower spikelet has two stamens and two feathery stigmas and is attached to a fuzzy plume that later assists the wind-dispersed seed in drifting through the air. In temperate areas cogongrass usually flowers from late winter through May or in the fall after the first frost. It may flower year-round in more tropical areas.
Vetiver grass (Vetiveria zizanioides) may be confused with cogongrass in tropical regions, but vetiver's leaf blade is grooved, rather than flat, and its overlapping leaf bases look flat, rather than rounded. When no flowers are present, cogongrass may look somewhat similar to Johnsongrass (Sorghum halepense), but cogongrass leaves are longer and the stems are not so evident. Brazilian satintail (Imperata brasiliensis) has one stamen per flower whereas cogongrass has two. The cogongrass cultivar 'Rubra' has burgundy foliage. 'Red Baron' has cranberry-red leaf tips with coloration that extends down the leaf blades and intensifies as the season progresses. Both are taxonomically classified as Imperata cylindrica var. rubra, whereas the more common yellow-green cogongrass of Asia and the southeastern United States is I. cylindrica var. major. (The African variety is africanus; europa is found in the Mediterranean region; latifolia in northern India; and condensata in Chile.) The rubra cultivars are cold-tolerant, low-growing forms that stay under about 1 ft (0.3 m) tall. Some nurserymen claim that these red varieties do not set seed or become invasive like the all-green forms, but ecologists contend that they can be aggressive. There is evidence that the red pigmentation is largely a response to colder temperatures; when planted in Florida or grown in a warm greenhouse, 'Red Baron' has been observed to revert to green.
Cogongrass, Imperata cylindrica, originated in Southeast Asia, the Philippines, China, and Japan. It is now distributed throughout the tropical and subtropical regions of the world. Over the past 50 years, cogongrass has become widely established in the southeastern United States. It invades a wide variety of habitats including swamps, floodplains, dry scrubs, and sand dunes, as well as the sandhills, roadsides, pastures, utility rights-of-way, and mined lands where it is most commonly observed.
CultureCogongrass usually occurs on highly leached acid soils with low fertility and minimal organic content. It seems to do best at a pH around 4.7. Cogongrass is easy to grow. Controlling it is another matter. The best approach is to burn or mow it in the early summer, let it put some energy into new growth, then apply an imazapyr herbicide (Arsenal® is one brand) in late summer, then come in a few weeks later and till the site and plant a competitive imazapyr-resistant cover crop such as hairy indigo (Indigofera hirsuta). Where this drastic a treatment is not possible, you can apply herbicide in the fall when the plant is translocating carbohydrates to its roots and it will transport the herbicide into the rhizomes too. Imazapyr seems to be the most effective herbicide, but glyphosate (Roundup® is one brand) is also a good choice. You'll still need to hand-pull every remaining shoot you can find -- again and again and again. You cannot eliminate a stand of cogongrass by approaching the task in a calm rational manner. To effectively do battle with this species you must alter your mindset and think of it as controlled by evil spirits. Only then will you become sufficiently paranoid to notice the sprigs slipping in amongst your daylilies or the brashly vertical yellow-green blades lit by the afternoon sun on the far side of the lawn. Light: Some horticulturists recommend growing the red varieties in part shade, but the common green cogongrass thrives in full sun. Moisture: Moist soil is recommended for cultivation of the red cultivars but in the wild cogongrass grows more competitively on dry sites. Hardiness: USDA Zones 5 - 9. Careful nurturing and heavy mulching may be necessary to get this species to survive its first few winters in zones 5-6. Propagation: Cogongrass responds to stress by producing more rhizomes and more flowers, but the seed produced from such off-season flowering may not germinate. Stress is not necessary to initiate seed production; many plants bloom regularly on undisturbed sites. Cross-pollination is required for the production of viable seed, however. Cogongrass is usually spread by wind-borne seeds or transported in fill dirt. The seeds do not require a dormant period. They can be planted immediately and will germinate within 1-2 weeks. In storage, they will remain viable for over a year. The seedlings are frail; less than 20 percent can be expected to survive. Cogongrass spreads rapidly from rhizomes. One node can send out enough branching shoots to produce 350 new plants in as little as six weeks. Severed roots remain viable in the soil for many months and can send up new top growth long after it appears that all the cogongrass has been eliminated from an area.
Cogongrass has been used in folk remedies for cancer, colds, diarrhea, dysentery gonorrhea, myalgia, night sweats, piles, rheumatism, and tumors. Stands of this species are sometimes burned or cut so that the tender new growth can be used for short term supplemental or emergency pasture, but it generally produces poor quality forage and animals avoid chewing the sharp-edged mature leaves. Cogongrass is often planted for soil stabilization and sometimes used for roofing thatch.
Because it is so tough, lush, and unpalatable, cogongrass has been recommended for landscaping zoo enclosures. It is difficult to imagine adequately controlling its spread in such situations, however. In the landscape, the red varieties can create glorious stained-glass effects when they are planted where the early morning or late afternoon sun lights up the leaves from behind. If you have the proper security clearance for handling plutonium shipments, you might be trustworthy enough to plant it this way and keep the flowers and shoots carefully trimmed so that it cannot spread. Cogongrass is too big a risk for the rest of us.
Cogongrass ranks number seven on the list of the world's worst weeds. It is an extremely aggressive species that will invade healthy natural communities and established pastures as well as disturbed sites. The Plant Conservation Alliance lists it as an Alien Invader, the USDA considers it a Noxious Weed, and the Florida Exotic Pest Plant Council lists it as a Category I Invasive Exotic Species. It is illegal to transport cogongrass into or within the United States and several states (including Florida) have laws that forbid growing or selling it. The reasons for such concern are compelling: Cogongrass has proven that it is capable of converting vast acreages of biologically diverse landscape into monospecific low quality grasslands. Its aggressive rhizomatous roots, secretions of allelopathic toxins, and ability to smother surrounding vegetation with a dense thatch allow it to choke out competition. Its flammability enables it to alter fire regimes to favor its own perpetuation. When cogongrass invades a new habitat, it increases fire frequency, intensity and flame height, which can drastically magnify fire hazards. The rhizomes survive and resprout vigorously after the top growth is burned off.
Linda Conway Duever 10/14/00; updated 12/26/03