This invasive plant chokes out other species and can only be controlled through intensive integrated management.
- Cogongrass in Florida
- Plant Structure
- Forage Value
- Methods of Control
- Integrated Management
Cogongrass is an aggressive perennial grass that is distributed throughout the tropical and subtropical regions of the world. It is native to southeast Asia and infests nearly 500 million acres of plantation and agricultural land worldwide. Although it does not tolerate cool temperatures, it is found on almost every continent. Cogongrass does not survive in cultivated areas but becomes established along roadways and in forests, parks, and mining areas.
In the United States, cogongrass grows as far north as South Carolina and as far west as Texas. Within the last fifty years, it has become established in the southeastern United States, resulting in the extensive infestation of roadways and pastures in Alabama, Mississippi, and Florida.
During the 1930s and 1940s, the plant was introduced into Florida as a potential forage crop and for soil stabilization purposes. However, cogongrass was found to be of little economic benefit as forage and a potentially serious pest. Consequently, it was placed on the noxious weed list, which prohibits new plantings. Unfortunately, cogongrass has been spread by illegal plantings and unintentional transport in forage and in soil during roadway construction. It is now found throughout the state, from the Panhandle well into south Florida.
In Florida, cogongrass infests ditch banks, pastures, roadsides and right-of-ways, golf courses, and forests. It thrives in a variety of media--fine sand to heavy clay--and grows well in low-fertility soils. A few monocultures have become established on hundreds of acres of reclaimed phosphate mining areas in central Florida.
Cogongrass is a perennial grass that varies greatly in appearance. Young leaves appear light green, while older leaves turn orange-brown. In areas with killing frosts, the leaves will turn light brown during winter months and present a substantial fire hazard.
Leaves. Cogongrass grows in loose-to-compact bunches. Each bunch contains several leaves arising from a central area along a rhizome (an underground, horizontal stem). The leaves originate directly from ground level and range from one to four feet in length. Each leaf is ½ to ¾ of an inch wide with a prominent, off-center, white mid-rib. Finely serrated leaf margins contribute to cogongrass's undesirable forage qualities.
Seeds. Cogongrass produces long fluffy white seedheads. Most seed production occurs in the spring. Sporadic seedhead formation can also be induced by mowing, burning, or fertilization. The seeds--which are extremely small and attached to a plume of long hairs--can be carried long distances by wind and animals. Researchers are still investigating the spread of cogongrass by seed.
Rhizomes. The rhizomes of cogongrass are responsible for its survival and short-distance spread. Established stands may produce more than three tons of rhizomes per acre. The rhizome's specialized anatomy allows for water conservation, and it can penetrate up to four feet into the soil, although most rhizomes remain in the top six inches. Rhizomes may also release substances that inhibit the growth of other plants. As cogongrass density increases, all other vegetation may be excluded, preventing the normal succession of species.
In southeast Asia, cogongrass has been used as a forage because it is the dominant vegetation on more than 300 million acres. In these areas, it was found that only very young shoots--which lack the sharp points and razor-like leaf margins--should be grazed or cut for hay.
Cogongrass yields are relatively low--even under heavy fertilization--and usually do not exceed five tons per acre. The plants rarely attain the minimal level of crude protein (7%) needed to sustain cattle. Furthermore, the nitrogen, phosphorus, and energy content of cogongrass are very low, requiring supplementation for livestock.
Attempts at finding natural pests of cogongrass have met with limited success.
Pathogens. Although some pathogens have been isolated, none have been developed for effective control.
Shade. Cogongrass does not tolerate dense shade and dies back upon canopy formation on Asian rubber plantations. However, reports of invasion into old growth forests in Florida suggest that a more shade-tolerant ecotype has developed.
Cultivation & Herbicides. Burning, deep plowing or disking, cultivation, cover crops, and herbicides have been used with varying degrees of effectiveness. However, although tillage and herbicides will provide some control and suppression of cogongrass, long-term eradication is seldom achieved.
To eliminate cogongrass and prevent regrowth, the rhizomes must be destroyed. It has been shown that an integrated approach that combines burning, tillage (mechanical disturbance), and chemical applications provide the best solution for cogongrass management.
Burning or Mowing. Start your cogongrass management by burning or mowing the cogongrass to remove excess thatch and older leaves. This initiates regrowth from the rhizomes--reducing their biomass--and allows herbicides to be applied to only actively growing leaves, maximizing herbicide absorption into the plant. Ideally, burning should take place in the summer.
Tilling. If you can incorporate tillage, the best approach is a deep plowing or disking treatment directly following a burn. You must cut to a depth of at least six inches to ensure that most--if not all--of the rhizomes have been cut. Tilling further depletes the rhizome reserve through desiccation and increases the number of shoots per given area. This practice also requires a one- to four-month regrowth period before herbicide treatment.
Applying Herbicides. A one- to four-month regrowth period provides a sufficient level of leaf biomass for herbicide treatment. If you burn your fields during the summer, apply herbicides in the late summer or early fall--approximately one month prior to the average killing frost, depending on area. Despite extensive testing, only a few herbicides have been found effective against cogongrass. For more information about effective herbicides, contact your county Extension office.
Replacing Cogongrass with Desirable Plants. After achieving good control of the cogongrass, you must introduce desirable vegetation as quickly as possible to prevent cogongrass from re-infesting the area. Be sure to choose species that colonize rapidly and tolerate the residual affects of your chosen herbicide.
Unfortunately, cogongrass will eventually begin to re-infest in spite of control, so you must continue to remove cogongrass and treat re-infested areas before this grass can regain a foothold. Selective herbicide choices are limited; research is continuing in this area.
The Florida cogongrass problem continues to increase. Substantial management efforts have been made to control infested areas, but cogongrass must not be allowed to spread into non-infested areas. Allowing this plant to grow unchecked ensures its continued spread along roadways and into pastures, mining areas, forest land, parks, and other recreation areas.
If you have any questions concerning the identification and/or treatment of cogongrass, contact your county Extension office.
Cogongrass (Imperata cylindrica (L.) Beauv.) Biology, Ecology and Management in Florida (SS-AGR-52) by G. E. MacDonald, B. J. Brecke, J. F. Gaffney, K. A. Langeland, J. A. Ferrell and B. A. Sellers. Published by: Agronomy Department (rev. 11/2006).
Related Sites & Articles
- Aggressive weed becoming a menace worse than kudzu--IFAS News, July 5, 2008
- Center for Aquatic and Invasive Plants
- Control of Non-native Plants in Natural Areas of Florida
- Florida Department of Agriculture and Consumer Services (FDACS)
- Florida Department of Environmental Protection (DEP)
- Help Protect Florida's Natural Areas from Non-Native Invasive Plants
- IFAS Assessment of the Status of Non-native Plants in Florida's Natural Areas
- Invasive Weeds
- National Invasive Species Information Center--USDA