Cogongrass, an aggressive invasive species, has been causing problems in Alabama’s forests and fields for more than 20 years, but research performed by Alabama Extension’s Dr. Nancy Loewenstein and former Alabama Extension specialist, Dr. Stephen Enloe, has proven successful against the invasive species.
Because of its Asian origin, cogongrass is known to some as “Japan grass,” and the species found a home in Alabama in 1912 when it entered Grand Bay via packing material. Despite its existence in Alabama for more than 100 years, its presence has only progressed to invasive within the last 40 years. Today it is ranked the seventh most troublesome weed worldwide.
The Issue with Cogongrass
While cogongrass seeds have a short lifespans and poor seedling survival rate, it is the weed’s subterranean system of rhizomes that is hard to defeat. The rhizomes show tolerance to heat and water stresses and have strong aggressiveness and regenerative capacity. The cogongrass rhizome system typically accounts for up to 60 percent of the weed’s biomass, making it difficult to eliminate.
Cogongrass presents a serious concern within forestry production. Patches of the invasive species can be found throughout Alabama’s central and southern forests, and it is a troublesome weed wherever it penetrates, according to Loewenstein.
“Cogongrass is very competitive with seedling pine trees,” she said. “It’s also a game-changer when it comes to the ability to use prescribed fires in forestry production. Patches of congongrass burn extremely hot and therefore increase pine tree mortality— an undesired effect of prescribed fires.”
The species is also a growing issue for farmers who graze livestock and produce forage as patches are appearing across pastureland, presumably spread in hay.
Enloe and Loewenstein identified a timed spraying regimen using two herbicides previously identified to work on cogongrass that is effective against the weed.
“Cogongrass is not something that can be sprayed once and left alone,” Enloe said. “We wanted to study what it took to completely annihilate an entire patch.”
That’s exactly what they did when the duo discovered that using multiple, specifically-timed spraying applications of the herbicides glyphosate or imazapyrdissipated the weed’s rhizome layer and killed off entire patches.
“It’s very exciting because no one has ever shown it’s possible to kill an entire area,” he said.
Continuing Research Efforts
Finding a successful herbicide regimen is not the last stop on the way to ending the reign of cogongrass in Alabama.
“What we’re working on now is studying genetic variability and whether or not this plays into the effectiveness of the treatment strategies we’ve developed,” Enloe said. “We know genetic variability exist in cogongrass, and we need to know how this will affect the adjustment of our treatments.” Dr. Loewenstein will lead these research efforts in Alabama.
The article Pushing toward Cogongrass (Imperata cylindrica) Patch Eradication: The Influence of Herbicide Treatment and Application Timing on Cogongrass Rhizome Elimination can be found at http://wssajournals.org/toc/ipsm/7/3.