As a single plant, cogongrass is unassuming, bucolic even. But in dense stands, it is a powerful vegetative force that alters forests and forges monocultures. The plant, known as Imperata cylindrica, has established itself on tens of thousands of acres in Alabama, Mississippi and Georgia and on one million acres in Florida, and it’s spreading fast. “Cogongrass could become a greater threat than kudzu or Japanese honeysuckle,” says Stephen Enloe, an invasive plant specialist at Alabama’s Auburn University.
Cogongrass not only forms into thick mats of thatch and leaves that make it nearly impossible for native plants to survive, but it also burns hotter than native species. After a burn, a six- to 12-inch-deep rhizome network sends up new shoots, regenerating themselves as soon as a month after the fire. This resilience makes it a severe threat to forests, especially the pine stands that make up a major industry in the South. Cogongrass is estimated to cost Alabama alone more than $7.5 million per year in lost timber productivity.
Heeding the call of worried scientists and others, the federal government has spent millions in American Reinvestment and Recovery Act money to fight the weedy scourge. These funds are being used to detect and treat infested areas of cogongrass, says Stephen Pecot of the Alabama Cogongrass Control Center.
Very few methods fight cogongrass effectively, so researchers are developing new ones. Investigators are testing herbicides, deploying remote-sensing techniques for mapping large infestations and detecting incipient patches that may be obscured by trees or shrubs, and studying cogongrass genetics to better understand the plants across their U.S. range.
A study published in May in the American Naturalist reported that plants such as cogongrass grow best in nitrogen-rich soil, suggesting that lowering the nitrogen content—perhaps by boosting the number of nitrogen-devouring microbes in the soil—might work. Says Enloe: “With persistence, it can be dealt with, but it requires a lot of land managers to kick it up a notch.”