Mississippi battling vicious invader that spreads quickly, kills plants by stabbing their roots
Published 9:50 am Monday, November 18, 2019
JACKSON, MISS. – Mississippi is under attack from a seemingly unlikely invader — a plant so invasive that it cannot be moved without a permit.Designated as the seventh worst weed in the world, one stem of cogongrass can produce over 40 square feet of other densely packed stems. Each stem has a seed head loaded with thousands of seeds that can be spread by the wind.
Cogongrass chokes out native species for control of soil nutrients. Its roots excrete chemicals to deter growth of competing vegetation, and the rhizomes can stab roots, bulbs and tubers of native trees and plants.
The high silica content of the grass causes sores in the mouths of horses, cows and other livestock. Not even goats find cogongrass an acceptable forage.
Imperata cylindrica, more commonly known as cogongrass, was introduced, accidentally and purposely, from East Asia to the southern United States in the early 1900s.
“Cogongrass is a highly invasive weed that the Mississippi Forestry Commission (MFC) is actively working to eradicate,” said Russell Bozeman, MFC state forester. “We are constantly working with our landowners to help identify and eliminate this devastating plant.”
The planty is regulated as a federal noxious weed. It is also a state noxious weed in Mississippi, meaning it cannot be moved within the state boundaries without a permit from the Department of Agriculture and Commerce Bureau of Plant Industry.
Background and History
In Mississippi, cogongrass was introduced as a new forage crop. Unfortunately, cogongrass is not palatable for livestock.When it failed as a forage crop, cogongrass was thought to be suitable for soil stabilization because of its vigorous growth and sturdy root system. However, cogongrass was found to be too weedy for erosion control.
With no native competition or consumers, cogongrass quickly spread from ports and experimental plots to prairies and pine forests throughout the Gulf South.
Estimates show that there are around 2 million acres covered in cogongrass from South Carolina to Florida and west all the way to Texas. In Mississippi, cogongrass is most densely populated in the southeast portion of the state, but stands can be found as far north as Saltillo and as far west as Vicksburg.
Controlling the spread
As cogongrass began its spread across the southeast, there were little efforts to manage the weed. Eradication was recommended as early as 1948.
One main issue with the continued spread of cogongrass was lack of public knowledge about the dangers it posed. A mature stand of cogongrass is attractive, with its dense mat of white-tipped stems. Some nurseries even encouraged its spread by selling the weed as an ornamental called “Japanese blood grass.”
Cogongrass is relatively easy to identify – it is the only grass with a white seed head in Mississippi in the early spring. A closer look at the plant shows the main vein of the leaf to be visibly off-center and the leaves have a fine serrated edge.
Research into the control and eradication of cogongrass heightened when the weed began to infest timber stands across the Southeast. Mississippi State University (MSU) began its cogongrass research in 1996.
Over the last 20 years, MSU weed science researcher Dr. John Byrd and his team have been looking at various methods to control and, hopefully, eradicate cogongrass from Mississippi. MSU has looked at burning, tilling, planting systems and herbicide application as ways to help stop the spread.
It has been found that fire is not an effective tool for combating cogongrass. Cogongrass grows in dense patches, creating a large volume of combustible biomass that can burn in excess of 800 degrees – hot enough to burn trees and other plants.
Additionally, cogongrass has been found to come back in full force after a controlled burn. Its extensive root system allows it to re-establish quickly and choke out native species in the area. Compounding the issue, cogongrass seeds thrive on bare soil.Broadcasting or drilling fast-growing crops, such as soybeans, into cogongrass has been an effective control method. Once the crop is planted, an application of glyphosate is necessary.Frequent tillage, with a rotary tiller, is a successful control method. Tilling breaks apart the rhizomes causing the plant to use its energy trying to regrow, rather than spreading.Landowners using this control method should clean tillage equipment before it leaves the site to prevent spreading the weed to other sites. The tilled site should also be replanted with some another plant that establishes itself quickly.The MFC helps landowners control the spread of cogongrass through herbicide application. Herbicides, such as imazapyr and glyphosate, have been shown to eliminate cogongrass through aggressive, repeated applications.Imazapyr is active in the soil and attacks cogongrass roots and rhizomes directly. Imazapyr remains active for several months, preventing new growth and spreadingGlyphosate is absorbed through the leaves and transported to the root system where it attacks the plant’s carbohydrate storage system, starving the plant of essential nutrients.“Herbicide application can be costly,” Bozeman said. “This is why the MFC has its Cogongrass Control Program, to help offset some of the expenses landowners incur.”Cogongrass continues its spread across Mississippi, despite federal and state transportation regulations. It continues to threaten forests, rangelands, natural areas, roadsides and residential areas.“Cogongrass negatively affects pine productivity and survival, wildlife habitat, recreation, native plants, fire behavior and site management costs,” said Bozeman. “Its ability to rapidly spread and displace desirable vegetation makes it particularly dangerous to native ecosystems.”