Cogongrass

General Information

Cogongrass, Imperata cylindrical (L.) P. Beauv., is often categorized as one of the top 10 worst weeds in the world and is perhaps the worst potential invader on our borders.  Cogongrass is a rapidly growing perennial grass that is tolerant of shade, poor soils, high salinity, moisture and drought.  Cogongrass can invade pastures, natural or planted forests, riparian areas, highway rights-of-way, urban areas and wetlands.  It is native to Southeast Asia and was introduced into the U.S. in 1911 near Mobile, Alabama, as packing material in shipping containers.

Cogongrass under pine forest

Figure 1.  Cogongrass can form dense stands under forests.  This interferes with forest management and regeneration.  Photo courtesy of Chris Evans, Illinois Wildlife Action Plan, Bugwood.org.

Currently, cogongrass infests over 1 million acres (400,000 ha) in the Southeast (Fig. 1).  Infestations are most widespread in Alabama, Florida, Mississippi, and Georgia but also occur in Louisiana, South Carolina, Texas, Virginia, and Oregon.  To date, cogongrass has not been reported in Arkansas.  Infestations have been reported just across the Mississippi River and experts fear that it is only a matter of time before the noxious weed enters Arkansas.

Cultivated "Red Baron" cogongrass

Figure 2.  Ornamental cogongrass is sold under several names such as Japanese bloodgrass and “Red Baron” bloodgrass.  Photo courtesy of David Teem, Auburn University, Bugwood.org.

A cultivated variety is already in the State.  A reddish colored ornamental grass called Japanese bloodgrass or Red Baron bloodgrass (Imperata cylindrica ‘Rubra’) (Fig. 2) has been planted by homeowners for the past several years.  These seemingly harmless plants can lose the red color and revert to the weedy and invasive cogongrass.

Cogongrass and all of its ornamental cultivars are Prohibited Plants in Arkansas.  It is illegal to grow, buy, barter or give away any of these plants in the state.

 

Cogongrass rhizome fragment

Figure 3.  Cogongrass can be spread when rhizome fragments are moved in soil accumulated or forestry or farming equipment.  Photo courtesy of Wilson Faircloth, USDA Agricultural Research Service, Bugwood.org.

Biology

Cogongrass spreads naturally by rhizomes (Fig. 3) and windblown seed (Fig. 4).  Seed may also be carried on vehicles or on mowers and other machinery.  Rhizomes and viable vegetative plant parts may be spread through soil on equipment and through fill dirt, as well.  The seed requires light for germination, which favors establishment in open and disturbed areas having little plant competition.  Seedlings are frequently found in sites disturbed by clear-cutting, burning, tillage, excavation, or grading.  New plants grow quickly and begin to produce rhizomes about four weeks after emergence.

Cogongrass seed head

Figure 4.  Cogongrass produces light windblown seeds that can be move long distances by wind.  Photo courtesy of Chris Evans, Illinois Wildlife Action Plan, Bugwood.org.

Here is a fact sheet from the University of Arkansas Division of Agriculture and some additional materials to introduce you to cogongrass.  You may also find this fact sheet at your local county extension office or Arkansas’ Cooperative Extension Service web site, www.uaex.edu.

Cogongrass:  A Potentially Invasive Weed in Arkansas

 

Identifying Cogongrass

Cogongrass resembles a few of our native grass species.  To learn how to tell the difference between cogongrass and other grasses, follow this link to University of Georgia, Center for Invasive Species and Ecosystem Health.

Key Identification Features of Cogongrass

To learn how to identify cogongrass, watch this video produced by the Mississippi Coastal Plains RC&D Council and the Mississippi Farm Bureau Federation.  It includes excellent instruction on identifying the grass in the field (and the blues music is nice, too).  The video is a large file and can take a while to load.

Cogongrass:  The Perfect Weed

 

Stop the Spread

Effective cogongrass control includes good sanitation to prevent spread of seeds and rhizomes.  Vehicles, ATVs, and machinery should be inspected for the fluffy seed and possible rhizome contamination after being used in infested areas.  Use of biological controls has been largely unsuccessful.

The following three paragraphs describing cogongrass control are excerpted from Identifying and Controlling Cogongrass in Georgia.

“Cogongrass control varies according to the age and rhizome mat density and depth.  Young infestations are usually easier to control than older well-established infestations.  For newer patches, tillage can eliminate cogongrass from an area if continued during the course of a growing season.  The initial tillage should begin in the spring (March through May) with an implement that tills the soil to a depth of at least 6 inches.  Perform additional tillage with a disk harrow or other appropriate implement every 6 to 8 weeks.  It is important to clean all equipment on site to prevent the spread by rhizomes.

“Dry periods during the summer will aid in the control of cogongrass.  The area can be planted to a fall cover crop and then followed the next season with perennial or annual grass or broadleaf crops.  Mowing may help reduce cogongrass stands, but areas must be mowed frequently and at a low height.  Monitor the site throughout the growing season; spot treat any recurring infestations with appropriate herbicides.

“Tillage may not be an option on many sites such as steep slopes, established tree plantings, or around dwellings.  Out of dozens of herbicides tested for significant activity on cogongrass only two, the active ingredients glyphosate (Roundup, Glypro, Accord, etc) and imazapyr (Arsenal, Arsenal AC, and Chopper), have much effect on this grass.  Even at high rates and using tank-mix combinations, cogongrass often regenerates within a year following a single application of either product.  A minimum of two applications per year is needed, realizing that older infestations may require 2 to 3 years of treatment to eliminate rhizomes.  Glyphosate has no soil residual activity.  Imazapyr has both soil and foliar activity and can severely injure susceptible plant species that are planted too soon after the last treatment.  Most vegetables, row crops, and ornamentals will be injured if planted with 24 months following an imazapyr application.  As with all pesticides, proper handling and usage is of utmost importance and always read and follow label directions.

The Alabama Department of Transportation has a guide that includes detailed instructions on preventing the spread and controlling established cogongrass along road sides and highways.

Mapping, Control, and Revegetation of Cogongrass Infestations on Alabama Right-of-Way

 

Resources

For more information and resources about identifying and controlling cogongrass, see the following websites and fact sheets.

Alabama’s Cogongrass Control Program (Alabama Forestry Commission)

Cogongrass (University of Georgia)

Weeds Gone Wild (National Park Service)