May 1, 2008
Invasive Grass Gobbles Up Acreage In Florida
By Leslie Kimel
At first glance you might think it’s kind of pretty. Yellow-green leaves ripple in the breeze, and silvery, plume-like seedheads catch the light.
But “pretty” isn’t the word Ed Barnard would choose. “This is one nasty weed,” he said.
It’s Imperata cylindrica, also known as cogongrass or speargrass, and by any name it’s a menace.
Barnard, a forest pathologist with the Florida Division of Forestry, says it’s become a major problem on state forestland.
“Certainly cogongrass is one of the worst weeds, if not the worst with which we are dealing,” he said. It might, he added, be “even more problematic than kudzu.”
Cogongrass is native to Southeast Asia, but you can find it today on every continent except Antarctica. In 1912 it slipped into the United States through the Port of Mobile, in Alabama, in the form of packing material in crates of citrus. Later, the U.S. Department of Agriculture promoted its use as a forage grass and soil stabilizer. It was introduced into Florida in the 1930s.
As forage, cogongrass was an immediate flop; even goats shun its tough, razor-edged leaves, which contain silica crystals that cut up the gums and the mouth. It wasn’t much good for erosion control either, since it inevitably revealed its weedy nature and ran rampant. A single plant can produce thousands of seeds, which can travel for miles on the wind. Cogongrass also reproduces vegetatively. It has a massive system of roots and runners, and even just a tiny fragment of a rhizome can produce a whole new plant.
Cogongrass isn’t something people plant on purpose anymore. It’s federally listed as a noxious weed. But people are still helping it spread, even though we don’t mean to. We move the vigorous rhizomes to new spots through contaminated fill dirt, sod, and hay. We pick up hitchhiking rhizomes and seeds on mowers and other equipment.
“Cogongrass is often spread by people who unknowingly move contaminated soil for road fill,” Barnard said. “If there’s cogongrass on the roadside and workers are grading the road, they can spread it by simply moving the runners with the blades of their machinery. Forest activities can spread it too. If you drag a fire plow through an existing population of cogongrass, that just drags the runners and opens up the soil and spreads the weed on a local scale. If somebody is harvesting timber and working in an area where there’s cogongrass and they load their machinery back onto a truck, move to another area, and then unload the truck, they may be bringing cogongrass with them.”
Cogongrass thrives in sun and shade, in rich soils and poor ones. It tolerates both drought and flooding. It is widespread throughout Alabama, Mississippi, and Florida, with scattered populations found in Georgia, South Carolina, Louisiana, and Texas. Cogongrass infests roadsides, old mining sites, electrical utility rights-of-way, pastures, fallow fields, forests, and parks. Wherever it goes, it creates a laundry list of ecological problems.
“Unchecked and where it develops into a monoculture, cogongrass literally displaces native species of plants, and that reduces habitat and food for native animals,” Barnard said.
Cogongrass itself has essentially no wildlife value.
“The leaves are not readily browsed because their edges are sharp and serrated,” said Rick Williams, extension forestry specialist at the University of Florida’s West Florida Research and Education Center. “And the seeds are just small, windblown seeds, so they aren’t a good food source. Cogongrass is displacing the native grasses and forbs that do produce good seed and are used as food by native wildlife. So a stand of cogongrass is like a little desert. There’s no good food. And stands are so dense that quail and turkey can’t even travel through them.”
Cogongrass destroys habitat. It also alters normal fire behavior.
“It raises the hazard for wildfire because it creates a fuel source that is extremely flammable at certain times of the year,” Barnard said. “Cogongrass burns hotter than the native grasses, so you may see fire damage to the stems of pines, which are fire resistant under normal circumstances.”
Cogongrass has tremendous impact on the forest industry. Besides being a fire hazard, it competes with young trees that foresters are trying to establish.
“Trees won’t regenerate naturally in cogongrass, and if you plant in it, it’s going to out-compete your seedlings,” Williams said. “The new trees will either not get enough water and nutrients and die or they won’t get enough water and nutrients to grow properly so they’ll just kind of sit there.”
Row-crop agriculture is less affected by cogongrass because tilling and cultivation tend to keep the weed at bay.
“Tilling does keep it out,” Williams said. “What you end up with though is that it gets all around the edges of your field. So it’s reducing your wildlife cover in your fence rows. And if you don’t till in your agricultural area, the cogongrass will start moving back in, and it can be a pretty tough competitor.”
Right now, there is no biological control for cogongrass and it is best managed with chemical herbicides. Herbicides are usually applied in the late summer or fall, preferably after the infested area has been burned or mown. Applications often need to be repeated year after year, and timing is important.
“Spraying is not effective in a drought situation,” Williams said. “It only works when the grass is green and growing and can take up the chemical and move it around.”
The Florida Division of Forestry is urging homeowners and landowners to be on the lookout for cogongrass. If you find cogongrass on your property, you should contact your local county extension agent or county forester for specific advice about treating it.
“Cogongrass is pretty easy to identify,” Barnard said. “It’s a pretty tall grass, about two to four feet high. The leaf blades are distinct in that the mid-rib is not in the center—it’s lopsided. The seedhead is pretty notable too; it looks like an elongated fluffy bottlebrush. And then there’s the reality of the enormous runners. If you dig it up and find runners all over the place, that’s a pretty good clue that you’ve got cogongrass.”
For more information about cogongrass and other invasive non-native plants, visit the Division of Forestry’s website at www.fl-dof.com.
