Auburn University researchers study wicked weed’s role in pine decline

AUBURN – A team of Auburn University scientists has been awarded a $494,000 grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture to search for possible links between cogongrass and pine decline – two biological phenomena that pose serious threats to Alabama, both ecologically and economically.

The researchers, led by College of Agriculture invasive plant specialist Stephen Enloe, want to determine whether the rapid spread of cogongrass across Alabama is increasing pine trees’ susceptibility to pine decline, a syndrome that is jeopardizing the health and survivability of loblolly pine plantations statewide.

Cogongrass, which ranks seventh on the list of the world’s worst weeds, is a hardy, aggressive grass that can ruin native ecosystems in countries outside its native Asia. It invades forests, pastures, rights-of-way and other noncultivated areas, as well as recently disturbed land such as newly established pine plantations and road construction sites. If left unchecked, it forms deep, dense mats of thatch and underground rhizomes that quickly overtake and choke out most plant species. In addition, cogongrass is both highly combustible, fueling fires that burn hotter and blaze higher than typical fires, and fire tolerant, which means it rebounds from fires faster and more vigorously than native species.

In their three-year NIFA-funded project, the Auburn researchers are investigating the impact that cogongrass infestations have on loblolly, as well as longleaf, pine ecosystems, or, specifically, on the insect communities in those forests. In addition to Enloe, researchers include Auburn forest ecologist and invasive plant specialist Nancy Loewenstein, forest pathologist and entomologist Lori Eckhardt and entomologist David Held.

Forestry is Alabama’s number-one industry, and loblolly pines are a major player in that, accounting for 36 percent of Alabama’s 22.7 million acres in timberland. In recent decades, however, the health of many loblolly pine forests in Alabama and across the Deep South has been deteriorating, the growth rates slowing and the mortality rate rising. This trio of symptoms is characteristic of what the industry has labeled pine decline. Though no specific causes of pine decline have been identified, scientists say that comparison of the roots of symptomatic trees with those of healthy pines shows the ailing ones have higher numbers of invasive, root-feeding pine beetles than healthy trees and are commonly infected with two specific pathogenic fungi.

“We know that cogongrass and the increased risk of intense fires it presents play havoc on a forest ecosystem’s natural vegetation, but no one has looked at whether there’s a cascading effect on the species and populations of insects,” Enloe says. “Our top goals are to find out how cogongrass infestations, as well as the herbicides and other management strategies being used to control the weed, alter insect diversity and abundance in those loblolly pine forests showing symptoms of pine decline, especially the insects that are vectors of the fungi associated with the syndrome.”

The cogongrass and pine decline project includes not only a strong research component but an active extension element as well.

“Throughout the project, we will be sharing our findings with forest landowners and managers through a number of outreach events, offering science-based cogongrass-control recommendations that will help them improve the health and productivity of their forest stands,” Enloe said.

Cogongrass has plagued southwest Alabama for several decades, but the noxious weed has been spreading rapidly over the last decade, hitchhiking out of that area of the state on vehicles and equipment from around the state that had assisted in the post-Hurricane Ivan cleanup and rebuilding. It now claims at least 100,000 acres in 32 of Alabama’s 67 counties. So menacing is the plant to the state’s economy and environment that late in 2009, Alabama was awarded a $6.28-million federal grant to be used solely to “control, mitigate and eradicate” cogongrass.

(Contributed by Jamie Creamer.)

Contact: Jamie Creamer, (334) 844-2783 (jcreamer@auburn.edu), or
Mike Clardy, (334) 844-9999 (clardch@auburn.edu)

Cogongrass has white, plume-like seed heads and bright yellow-green leaves with finely serrated edges. Cogongrass invasions deliver blows to pine productivity and survival, wildlife habitat, pastureland, native plants and normal fire regimes.

Stephen Enloe, standing, right, and crew sample a plot of cogongrass in Mobile County to gather data for the new project. The invasive grass that is one of the world’s top 10 worst weeds is making itself known across Alabama.