At first sight, the striking grass commonly sold as an ornamental cultivar called ‘Red Baron’ or bloodgrass makes an attractive addition to the landscape, but beware: this ornamental plant can become an invasive problem for vegetable and fruit growers. Known as Imperata cylindrica, cogongrass ranks as one of the 10 worst weeds in the world. Cogongrass is a species of grass in the genus Imperata. It is a hostile intruder of both natural and disturbed sites.
Ranging in height from 2 to 6 feet, the plant contains whitish, branched rhizomes that are scaly and contain sharp tips. Cogongrass can be easily identified in spring by the large fuzzy flowers and seeds, giving the plant a silky appearance.
Aggressive, cogongrass has the potential to take over open spaces – orchards being a target area. The plant sneaks into vegetable fields in untilled areas and soon takes a foothold on produce. Being highly flammable, the strands of the grass ignite quickly and create a severe fire hazard. Burning extremely hot, the plant may change fire management. Not only are fruit orchards and vegetable fields at risk, but equipment in the fields can produce a great loss. Add to this concern chemicals ready for distribution and gasoline-powered machinery nearby.
The origin of cogongrass
Like many other aggressive weeds that surface in the U.S., its origin may never be known. It is thought to have originated in East and Southeast Asia, India, Micronesia, Australia and East and South Africa.
In the early 1900s, it is thought that cogongrass was accidentally introduced into the United States in packing material. And like kudzu, this plant was used purposely as erosion control and for livestock forage.
Considered a southern invasive plant, cogongrass is now established in Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and Texas. As of May 2010, all known infestations in South Carolina, Georgia and Tennessee are under treatment and are in the process of being eradicated. (Center for Invasive Species and Ecosystem Health, University of Georgia in Cooperation with States, May 2010.)
Adaptable to many growing conditions, the grass is difficult to control. This hardy plant tolerates shade and thrives during a drought, and cogongrass has been identified growing on sand dunes, along roadsides, in uncultivated fields and borders standing water.
A grass on the move
A hardy perennial grass, the plant forms dense mats and puts up shoots 6 feet in height. Both by reproducing vegetatively (rhizomes) and from seeds, this plant is very prolific. It is estimated that one mature plant can produce over 3,000 seeds. However, the plant has a relatively short life span: less than one year.
As the sharp-pointed rhizomes are resistant to heat, a control burning may not rid the area of this invasive plant. Even tilling the area and breakage of the root may not eradicate the plant. It has been found that the rhizome may penetrate the soil up to 4 feet deep. When rhizomes, even less than 1 inch, are left the plant regenerates. These factors make control extremely difficult.
Other than regeneration, seeds and rhizomes are spread from orchards and vegetable plots by farm equipment. After working in the area, farm tractors may have seeds hitching a ride on the radiator. Another source of infestation comes from utility equipment, including mowers along roads and highways. Like other means of transporting seeds from one location to another, the extremely small kernels hitch a ride on the hair and fur of animals, and on the clothing of growers or farmers. The lightweight seeds can also be picked up and moved by the wind.
However, rhizomes are the basic method of distribution. A unique feature of the plant is that they are allelopathic, meaning that a chemical is exuded in the rhizome that retards other nearby plants from thriving. This substance combined with the dense protection mat gives cogongrass a stranglehold over nearby plants.
Vegetable farms and orchards bordering highway rights-of-way are often at risk for infestation. If road construction, maintenance or repair work is performed nearby, this plant may become a threat to fruit and vegetable growers. Contaminated equipment brings in rhizomes from other areas for site preparation, fruit and nut tree planting and wildlife food plot preparation. Another source is fill dirt purchased from companies that deal with site preparation. Growers will agree: preventing the spread of seeds and rhizomes is critical to control this invasive plant.
Control and eradication
Dr. Gregory R. Armel, assistant professor, extension specialist for invasive weeds, University of Tennessee, makes this recommendation: repeated herbicide treatments are usually recommended, with disking or mowing following an application of imazapyr being the most effective treatment (www.utextension.utk.edu/publications/ pbfiles/PB1785.pdf).
Another option is to use an herbicide application of glyphosate (Accord). In about 35 days, the top growth appears brown. Use another application in September using 20 gallons per acre.
The goal of controlling or killing cogongrass is to eliminate the deep underground rhizomes. It’s the top growth that is easier to destroy. The older the established rhizomes and mats, the more difficult to control. Those with rhizomes reaching and intertwining over 5 inches will create a challenge. Look for centers of infestations where the deeper mats appear. Near the edge are younger plants that continue to spread if left untreated.
Vegetable and fruit growers can use tillage in small areas when planned over one or two growing seasons. If caught early, small areas can be manually dug with a shovel or plants can be pulled out by hand. Remove all plant material and destroy.
However, tillage or mechanical plowing and cultivating are challenging. Some researchers believe this process spreads the rhizomes. Others believe it brings the deep rhizomes to the top of the soil, where they can be treated by repeated herbicide applications.
This pesky weed adapts well to poor soils, as well as low pH soils with low organic matter. The rhizomes, due to the dense mat, produce a soil that is extremely drought-tolerant. Usually located in the top 6 to 10 inches of soil, they may run as deep as 4 feet under the surface.
Another reason for the plant to be a strong survivor is the ability to adapt to low light conditions. It is estimated the plant can thrive on less than 5 percent sunlight. This quality makes cogongrass a threat to fruit orchards and nut farms, where it thrives under the dense tree branches. The density of the rhizomes can stunt the growth of fruit and nut trees.
Using prescribed burning may help eliminate cogongrass. However, the plant is tolerant of fire and burns 15 to 20 degrees Celsius hotter than normal understory fires, which may harm nearby vegetation.
Using livestock or animal feeding as a control method may offer some help. Horses and goats, when contained in a small area, have been successful in some areas.
For the future, introducing rhizoctonia disease as a biological control is being studied.
Stopping the spread
Cogongrass is considered a federal noxious weed and is on the Pest Plant List in several southern states. Any infestation must be identified and reported to the appropriate state or federal authorities. Contact your state Department of Agriculture. Identification and eradication are vital to containing the spread of this plant.
Following is the information you should be ready to provide:
- Site or location of the cogongrass (county, city, street address, road name/mile marker, GPS coordinates)
- Size of infestation (approximately)
- Is it flowering?
- Contact information
Clemson University in South Carolina asked for volunteers to identify and report landscape plants being sold or sites where cogongrass is growing. Volunteers report to a site coordinator who sends an identifier to confirm the plant’s identity. This information is entered into a database for future treatment. The more volunteers, the greater the chance of cogongrass being eliminated.