Cogongrass [Imperata cylindrica (L.) Beauv.] is a warm-season, rhizomatous grass native to southeast Asia that has invaded thousands of hectares in the southeastern United States. Its negative impacts on pine forests have been well documented, and aggressive control is widely recommended. Although repeated herbicide treatments are effective for suppression, integrated strategies of prescribed burning coupled with herbicide treatment and revegetation are lacking in pine systems. In particular, longleaf pine forests, which are typically open, fire-dependent, communities, are highly susceptible to cogongrass, which is a pyrogenic species. To address management goals for cogongrass control and herbaceous restoration in longleaf pine forests better, field studies were conducted in southwestern Alabama from 2010 to 2012. Two longleaf pine forests with near-monotypic stands of cogongrass in the understory were selected for study. Treatments included combinations of winter prescribed fire, spring and fall glyphosate herbicide treatments, and seeding a mix of native, herbaceous species. Data were collected for three growing seasons following study initiation, and included seasonal herbaceous species cover and final cogongrass shoot and rhizome biomass. Species richness and diversity were calculated and analyzed to ascertain treatment effects over the duration of the study. Burning slightly improved cogongrass control with glyphosate, but had no effect on total cover, species richness, or species diversity. Three glyphosate treatments reduced total vegetative cover and nearly eliminated cogongrass cover, shoot, and rhizome biomass. Glyphosate and glyphosate seeding also increased herbaceous species richness and diversity. However, aboveground productivity in treated plots was significantly lower than productivity in the untreated control, which was almost exclusively cogongrass. These studies indicate that glyphosate and integrated strategies utilizing glyphosate and seeding are very useful for cogongrass management and increasing herbaceous species richness and diversity in longleaf pine.

Nomenclature: Glyphosate, cogongrass, Imperata cylindrica (L.) Beauv., longleaf pine, Pinus palustris Mill.

Management Implications: Cogongrass is a serious threat to southeastern pine ecosystems. Although numerous control studies have been conducted, information is still lacking for cogongrass management in longleaf pine. With longleaf pine, many land managers want to recreate mixed pine/open savannah conditions with a species-rich herbaceous understory. However, cogongrass is a significant obstacle to that goal, as it forms near-monotypic stands beneath longleaf pine that are of little value. To address this problem, we tested multiple integrated methods, including prescribed burning, glyphosate treatment, and seeding native herbaceous species. We found that glyphosate treatment following prescribed burning provided a minor but significant increase in cogongrass control compared to glyphosate-treated, unburned plots. However, the effect was short-lived and not useful when follow-up glyphosate treatments were applied. Glyphosate treatment combined with seeding native species generally increased cover, species richness, and diversity compared to glyphosate treatment alone. Burning and seeding without glyphosate treatment was ineffective, as cogongrass quickly recovered. In summary, we found that glyphosate treatment was critical for cogongrass control and improvements in native species richness and diversity.