Cogongrass Invades the South
It grows on every continent except Antarctica and has earned a reputation as one of the worst weeds on earth. Now, according to U.S. Forest Service emeritus scientist Jim Miller, cogongrass (Imperata cylindrica) is one of the most threatening invasive species in the South.
Native to Southeast Asia, cogongrass was accidentally introduced in the United States as packing material in an orange crate that arrived in Grand Bay, Alabama, in 1912. A few years later, it was intentionally planted as a potential forage crop in Mississippi and as a soil stabilizer in Florida.
And then it began to spread.
SRS Forest Inventory and Analysis data indicate that cogongrass currently grows on over 66,000 forested acres—and counting—throughout the southern United States. “This does not take into account the thousands of unsurveyed acres occupied by cogongrass in nonforested settings,” says Miller. “Because cogongrass is a fast moving and destructive plant that can thrive almost anywhere, the entire Southeast is at risk for invasion.”
Each cogongrass plant produces as many as 3,000 wind-dispersed seeds that can germinate on disturbed soil. Cogongrass also spreads by underground stems known as rhizomes that form dense mats reaching deep into the soil. The rhizomes have pointed tips that are sharp enough to pierce the roots of nearby plants. Rhizome shoots and branches expand into colonies that can completely exclude all other plants.
“The rapid spread of cogongrass can primarily be attributed to seeds and rhizomes that hitchhike on mowers, equipment, hay, fill dirt, and rocks being transported out of infested zones,” says Miller.
Cogongrass apparently tolerates all light and soil conditions except dense shade and permanently wet soil, so most habitats in the South are fair game. Once established, it is extremely difficult to control.
Fire doesn’t slow down the invader; cogongrass itself presents a serious fire hazard. The plant burns readily, even when green, and especially when the tops of plants dry and brown in the winter. Houses and other structures in suburban areas are increasingly at risk due to the unnaturally hot and fast wildfires produced by ignited cogongrass. Following a fire, the surviving rhizome system allows cogongrass to quickly regenerate and continue spreading.
The spread of cogongrass has so far been limited to temperate areas with relatively mild winters, but that could change.
Red Baron or Japanese blood grass, an ornamental variety of cogongrass used in landscape plantings, is cold hardy. As of yet, the cultivar does not produce viable seed, but it does have viable pollen.
“There is real potential for the cold hardiness bred into the red varieties to be imparted to invasive cogongrass populations through pollen,” says Miller. “If this occurs, the whole United States and southern Canada would be open for invasion.” This concern has prompted several Southern states to prohibit the sale and distribution of the cogongrass cultivar.
Proactive control and eradication of cogongrass and, ultimately, rehabilitation of infested lands in the South is an ongoing challenge. “Cooperation and education on a grand scale are needed to rid the South of cogongrass,” says Miller. “But preventing cogongrass from becoming established in the first place will be the best—and least costly—solution to this problem.”
For more information, email Jim Miller at jameshmiller@fs.fed.us .