Good News for Eradicating Cogongrass in the South

Research shows success using combinations of treatments and timing

by Zoё Hoyle, SRS Science Delivery Group
Cogongrass invading forested areas. Photo by Charles T. Bryson, courtesy of Bugwood.org.

Cogongrass invading forested area. Photo by Charles T. Bryson, courtesy of Bugwood.org.

Over the past decade, U.S. Forest Service researchers have been working with university cooperators to find some way to slow down or stop the relentless spread of cogongrass. This last fall, Auburn University researchers reported results that demonstrate, for the first time, that patches of cogongrass can be eliminated completely within three years — showing that eradication of the invasive plant is actually possible for many land managers.

Cogongrass is in a class of its own. Ranked the seventh worst weed in the world, it grows on every continent except Antarctica and is particularly destructive to the ecological structure of forests and natural areas, where the weed can literally take over understories.

Cogongrass currently occupies an estimated 66,000 forested acres in the U.S. South. It’s classified as a noxious weed in Alabama, Florida, Georgia, Mississippi, South Carolina, Texas, and Virginia, where it is widely believed to be impossible to eradicate. Estimated to spread 800 acres a year, cogongrass could infest 100,000 forested acres by 2060.

“Cogongrass grows mainly by extending rhizomes, which are like creeping rootstalks,” says Jim Miller, emeritus Forest Service Southern Research Station (SRS) researcher who helped with the study. “Cogongrass rhizomes are exceptionally aggressive, strong, and resistant to heat and water stress, making the plant a formidable and frustrating opponent.”

For the recently published study, researchers established a field study in two locations in southwestern Alabama where they applied herbicide treatments —  glyphosate, imazapyr, and a mixture of both —  in May, August, or October for three consecutive years.

“I consulted on experimental design, but Erwin Chambliss, senior technician with the SRS Restoring Longleaf Pine Ecosystems unit, did the heavy lifting for SRS, digging and separating rhizome samples in the field during the hot Alabama summer,” notes Miller.

The study found that although responses of cogongrass to the treatments varied by location, 36 months after the initial treatment cogongrass shoot and rhizomes were completely eliminated and 100 percent visual control achieved at both locations using several combinations of herbicide treatments and timing.

“The findings provide a ray of hope for actually eradicating cogongrass,” says Miller. “Land managers now have a clear option in fighting this noxious weed.”

In related news, the Georgia Forestry Commission’s Cogongrass Taskforce recently announced that for the first time since the Forest Service Southern Region’s Forest Health Program began funding cogongrass control in Georgia in 2004, there are more dead cogongrass spots in the state than new areas of cogongrass being reported.

The taskforce encourages citizens to report cogongrass occurrences and treats every infestation reported in the state, respraying as needed until the spots are negative for cogongrass for three years and receive “eradicated” status.

This effort confirms the hope that a weed that’s consumed millions of dollars in control efforts – and millions more in the economic and ecological consequences of cogongrass infestations – can indeed be eradicated in Georgia.

For more information, email Jim Miller at jamesmiller@fs.fed.us

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Posted in Forest Health Protection, Invasive Plants, Longleaf Pines, Restoration, Threats
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