Control of noxious weeds such as cogongrass depend heavily on chemical treatment, but success is limited unless integrated with other practices. Utilization of cover crops in the system is ideal to avoid the use of excess herbicide and replace vegetation that will resist cogongrass reinvasion. Greenhouse studies were conducted from 2013 through 2015 at Mississippi State University with the objective to evaluate ‘AG4934’ RR/STS soybean, Korean lespedeza, crimson clover and ‘Durana’ white clover tolerance to soil-applied imazapyr at selected rates and various planting times after application. Plastic containers filled with a mixture of 2:1 sand:topsoil were treated with imazapyr at 0, 70, 140 and 280 g ae ha–1. Legume species were planted 0, 1, 3 and 6 months after treatment (MAT). The factorial experimental design included legume species, imazapyr rate and planting time. At 6 weeks after each planting, the number of seedlings, average plant height and shoot biomass were measured. Statistical analysis revealed the imazapyr rate x planting time interaction was significant with respect to number of emerged seedlings, average height and shoot biomass per plant for each species. It was observed that the legumes planted at 0 MAT of imazapyr at 70 g ae ha–1 or higher reduced emerged seedlings, average height and biomass production. In general, seeds planted 1 MAT or later in combination with these same herbicide rates, showed less growth reductions than treatments seeded 0 MAT. In conclusion, sites treated with imazapyr rates from 70 to 280 g ae ha–1 for weed control, should not be seeded with legume ground covers less than 1 month after treatment to reduce emergence failure, plant height and biomass production.

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.

Cogongrass invades forests through rhizomatous growth and wind-dispersed seeds. Increased density and abundance of woody vegetation along forest edges may strengthen biotic resistance to invasion by creating a vegetative barrier to dispersal, growth, or establishment of cogongrass. We evaluated differences in dispersal of cogongrass spikelets experimentally released from road edges into tallgrass-dominated and shrub-encroached longleaf pine forests (Pinus palustris). Average maximum dispersal distances were greater in the pine–tallgrass forest (17.3 m) compared to the pine–shrub forest association (9.4 m). Spikelets were more likely to be intercepted by vegetation in pine–shrub forests compared to pine–tallgrass forests. Results suggest that dense woody vegetation along forest edges will slow spread from wind-dispersed cogongrass seeds.

Aminocyclopyrachlor (AMCP) is a synthetic auxin herbicide used for broadleaf weed control in pasture and rangeland. The tolerance and fate of AMCP within pertinent grass species is not well understood. Research was conducted to establish the tolerance of four grass species to AMCP application and observe their absorption, translocation, and metabolism. Results indicate that tall fescue is the most tolerant of AMCP at rates required for weed control. Bahiagrass and bermudagrass are marginally tolerant, and cogongrass is the most sensitive. Tall fescue and bahiagrass absorbed more AMCP than bermudagrass and cogongrass, but cogongrass absorption is the most rapid and complete within 2 days after treatment (DAT). Cogongrass and bermudagrass translocated the least amount out of the target area, whereas bahiagrass and tall fescue translocated the most. Radioisotope imaging revealed that tall fescue may sequester absorbed AMCP in leaf tips. This sequestering may be the basis of the greater tolerance to AMCP by tall fescue relative to the other species evaluated. No metabolism of AMCP was detected in any grass species out to 42 DAT.