Cogongrass Eradication
SOBS is actively involved in efforts to eradicate cogongrass from Marion County and Ocala National Forest. (See Invasive Species Control discussion above.) [Link “efforts to eradicate cogongrass from Marion County” to the Star-Banner pdf.] If you have information on cogongrass stands in Marion County or wish to volunteer to become involved in this project, contact Linda Duever at [LCD’s SOBS e-mail address].
Cogongrass (Imperata cylindrica) is the invasive species that poses the greatest threat to the Ocala National Forest. It is called the “Grass from Hell” for good reason. This grass is recognized as one of the world's worst weeds. It is an extremely aggressive and tenacious species that invades healthy natural communities and established pastures as well as disturbed sites. Cogongrass has proven that it is capable of converting vast acreages of biologically diverse landscape into monospecific low quality grasslands. It already covers hundreds of thousands of acres in the southeastern United States and tens of millions worldwide and it is still spreading rapidly. Aggressive deep-reaching rhizomatous roots, secretions of allelopathic toxins, and the ability to smother surrounding vegetation with a dense thatch allow it to choke out competition. In natural areas, cogongrass replaces native groundcover vegetation, decimating wildflowers, destroying wildlife habitat, and decreasing endangered species populations. Its extreme flammability enables it to alter fire regimes to promote its own perpetuation. When cogongrass invades a new habitat, it increases fire frequency, intensity, and flame height, which can drastically magnify fire hazards, threatening rural homes and timberlands and endangering the firefighters who protect them. Since cogongrass is low in nutrients and only palatable to livestock when the new shoots are fresh and tender, it ruins hayfields and severely degrades pasture quality. It overwhelms ornamental plantings and, because it is coarse-textured, fast/tall-growing, and oddly colored, it ruins the appearance of lawns.
Cogongrass is a bright chartreusey yellow-green perennial grass that grows 2-4 ft tall and forms dense stands excluding other plant species. The erect leaf blades are about 0.5 in wide and have a prominent whitish off-center midrib and a sharp tip. The leaves are flat and have saw-like edges lined with sharp microscopic silica crystals. The round leaf bases are sheathed and attached to short round stems. The upper part of the leaf blade is hairy near the base, but the underside is smooth. As the plants go dormant, the leaves turn grey-brown from the tips downward, giving the clumps a bronzy gold winter color. The dead leaves remain standing and resist decay. Cogongrass roots are sharp-pointed white barbwire-like rhizomes that branch readily and rapidly shoot out from one plant to form another, sometimes going right through the roots of intervening plants. Most of these rhizomes are interwoven in a dense mat within about a foot of the soil surface, but some may reach as deep as 3-6 ft. Cogongrass flowers are borne in conspicuous cylindrical silky white spikes 1-16 in long and 0.25-1 in in diameter. Each individual flower spikelet has two stamens and two feathery stigmas and is attached to a fuzzy plume that later assists the wind-dispersed seed in drifting through the air.
The Marion County Invasive Species Management Council plans to post current cogongrass control recommendations for various landscape situations on the county extension website. In the meantime, here is their advice about how to get rid of it:
The most important thing to know about controlling cogongrass is that it requires persistent repeated herbicide treatments to kill the rhizomes so that it won’t grow back. Spraying it just once or twice will only knock it back temporarily. At an absolute minimum, eradication requires retreating a stand twice a year for two to three years. Monitoring four times a year (continuing until there has been no sign of life for at least two years) and promptly herbiciding any fresh growth on each occasion is the most certain way to assure success. Robert Lamont says that their experience on Silver River State Park indicates that you need to keep coming back and retreating as soon as the shoots get 2-3 in tall.
Only two commonly available herbicides are effective against this species: imazapyr (marketed as Arsenal, Arsenal AC, or Chopper) and glyphosate (marketed as Roundup, Glypro, or Accord). Imazypyr will generally remove more cogongrass faster, but it is an extremely dangerous long-lasting herbicide that will kill nearby oaks and other desirable plants and leave the soil so toxic that hardly anything will grow there for years. Glyphosate also requires careful application, but it is less toxic to nearby trees and does not have longterm residual activity in the soil.
How the site is treated before and after herbicide use is a major factor in determining the effectiveness of the eradication effort. For optimum herbicide uptake, a cogongrass stand should initially be mowed, tilled, or burned in the early summer, then sprayed when fresh growth is active a couple of months later. (Care must be taken to prevent spreading cogongrass propagules or starting wildfires in the course of these procedures!) This removes the thatch so that the chemical contacts live foliage and assures that vigorous growth will carry the herbicide deep into the root system. As patches of cogongrass die, reinvasion must be preempted by promptly replanting these areas with highly competitive species compatible with the aftereffects of the herbicide used and the longterm management goals for the property.
Cogongrass control is most successful when a stand is attacked during its first couple of years, when the roots are still relatively shallow. After that, it becomes very difficult to get the herbicide all the way down into the long rhizomes.
Various mowing, pulling, shading, flattening, burying, tilling, and smothering strategies have been used as non-toxic or supplementary control methods with varying degrees of success. I have eliminated small quantities of cogongrass from flowerbeds with hand-pulling alone. Digging the roots up works even better.
The key is to prevent photosynthesis until the last deep roots die due to lack of nourishment from the leaves. If you keep at it persistently and consistently, never allowing foliage to develop, this will eventually work. But you have to keep checking the area and eliminating every last green blade each time you find new shoots -- and you have to keep this up every few months for at least two years after you believe it is all gone.
Some sources of additional information:
http://edis.ifas.ufl.edu/BODY_WG202
http://www.ag.auburn.edu/agrn//cogongrass/cogongrass%20fact%20sheet.htm
http://rcrec-ona.ifas.ufl.edu/IN012406.html
http://www.myakkariver.org/cogon_links1.html
http://www.floridata.com/ref/I/impe_cyl.cfm
http://www.invasive.org/eastern/srs/CG.html
http://www.fl-dof.com/forest_management/fh_invasives_cogon.html