Nancy J. Loewenstein

Non-native plants in the understory of riparian forests across a land use gradient in the Southeast

As urbanization expands into rural areas, an increase in the number of non-native plant species at the urban-rural interface is expected due in large part to the increased availability of propagules from ornamental plantings. A study investigating the distribution of non-native plants in the understories of riparian forests across an urban-to-rural gradient north of Columbus, GA was initiated in 2003. A significantly greater number of non-native plant species occurred at the urban sites and at one site at the urban-rural interface, where 20 to 33% of the species encountered were non-native. In contrast, at the more rural sites non-native species comprised 4–14% of the total number of species. However, the importance values of non-native species as a whole did not change significantly across the land use gradient due to the high frequency and abundance of three non-native species (Ligustrum sinense, Lonicera japonica, and Microstegium vimineum) in the majority of the watersheds. Reductions in species richness and overstory reproduction associated with these non-natives could impact long-term forest structure and ecosystem function.

Herbicide Treatment and Application Method Influence Root Sprouting in Chinese Tallowtree (Triadica sebifera)

Chinese tallowtree is an invasive tree found throughout the southeastern United States and in California. Its negative effects can be seen in numerous natural and managed ecosystems, including bottomland hardwood forests, pastures, pine plantations, and along lakes, ponds, streams, and rivers. Despite its troublesome presence for many decades, relatively few effective control strategies are available. Root sprouting following management efforts is a major impediment to successful control. Studies were conducted in Alabama and Louisiana at three locations to test several herbicides for cut stump, basal bark, and foliar individual plant treatment (IPT) methods. Herbicide treatments included triclopyr amine and ester formulations, imazamox, aminopyralid, aminocyclopyrachlor, and fluroxypyr. Data were collected just before leaf senescence at one and two growing seasons after treatment and included Chinese tallowtree foliar cover, number of stump or root collar sprouts, and number of sprouts originating from lateral roots within a 1-m radius of each tree. For the cut stump and basal bark studies, most herbicide treatments prevented sprouting from the stump or root collar region better than they did from the lateral roots. Aminopyralid reduced total sprouting better than all other treatments in the cut stump study. The high rates of aminocyclopyrachlor and fluroxypyr resulted in the highest mortality in the basal bark study. Aminocyclopyrachlor reduced total sprouting better than all other herbicides in the foliar treatment study. Triclopyr amine and ester formulations, which are commercial standards, did not consistently control Chinese tallowtree across these IPT studies. These studies provide some promising treatments to increase the number of effective tools that can be used to manage Chinese tallowtree. Additional research is needed to address the prolific nature of lateral root sprouting following any of these treatment methods. Nomenclature: Aminocyclopyrachlor; aminopyralid; fluroxypyr; imazamox; triclopyr; Chinese tallowtree, Triadica sebifera (L.) Small. Management Implications: Chinese tallowtree is an increasing problem across the southeastern United States. However, there is little published research examining effective control methods. We compared several newer herbicides with the commercial standards triclopyr ester and triclopyr amine for foliar, cut stump, and basal bark individual plant treatment (IPT) methods in natural areas. We examined both root collar and lateral root sprouting response to herbicide treatment, which is rarely done in invasive plant studies. We found that aminocyclopyrachlor, aminopyralid, fluroxypyr, and imazamox all controlled Chinese tallowtree similar to, or better than, triclopyr in specific IPT studies. Aminocyclopyrachlor resulted in greater mortality of Chinese tallowtree than triclopyr did in foliar and basal bark studies, whereas aminopyralid was more effective than triclopyr in cut stump studies. Fluroxypyr resulted in greater mortality than triclopyr in cut stump and basal bark studies but not in foliar studies. This research highlights the strong need to continue to evaluate new tools for invasive plant control and the need to continuously collect better data on invasive plant responses to treatment.

Impacts of Prescribed Fire, Glyphosate, and Seeding on Cogongrass, Species Richness, and Species Diversity in Longleaf Pine

Abstract 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.

Impact of cogongrass management strategies on generalist predators in cogongrass-infested longleaf pine plantations.

BACKGROUND Cogongrass (Imperata cylindrica Beav.) is an aggressive, invasive weed with a global distribution. In North America, it threatens the integrity of southeastern pine agroecosystems, including longleaf pine (Pinus palustris Mill.). While studies have examined the impacts of cogongrass and various vegetation management strategies on longleaf pine understory plant communities, little is known about how they impact associated insect communities. To understand the effect of cogongrass management strategies on arthropod natural enemies and bark beetles, a split-plot design was used to test fire (whole-plot) and four subplot treatments (control, herbicide, seeding and herbicide plus seeding). Arthropods were sampled using pitfall traps and sweep samples. RESULTS After 2 years of sampling, total natural enemies were not significantly affected by subplot treatment but were affected by burn treatment. Upon subdividing natural enemies into groups, only spiders were significantly affected by subplot treatment, but predatory beetles and ants were significantly affected by burn treatment. The abundance of root-feeding bark beetles (Hylastes spp.) was not significant by subplot or whole-plot treatments. CONCLUSIONS Multiple applications of herbicide remain the most effective way to manage cogongrass in longleaf pine. In this study, we found limited evidence that cogongrass management with herbicides would negatively impact arthropod natural enemies associated with longleaf pine or locally increase root-feeding bark beetles.

Pushing toward cogongrass (Imperata cylindrica) patch eradication: the influence of herbicide treatment and application timing on cogongrass rhizome elimination.

Abstract Cogongrass, an invasive grass native to Asia, has infested thousands of hectares in the southeastern United States. Although numerous studies have examined cogongrass control, no published studies, to our knowledge, have tested strategies for cogongrass eradication. Cogongrass has a persistent, thick rhizome mat but an ephemeral seedbank; therefore, successful eradication methods must largely focus on the rhizomes. A field study to evaluate specific herbicide treatments and application timings for cogongrass patch eradication was conducted at two locations in southwestern Alabama. Herbicide treatments included glyphosate at 4.48 kg ai ha−1, imazapyr at 0.84 kg ai ha−1, and a tank mix of glyphosate and imazapyr at the same rates. Treatments were applied in May, August, or October for 3 consecutive yr, and the May glyphosate treatment included a second annual application each October. Cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content were sampled during the course of the study. Cogongrass response to treatments varied by location but by 36 mo after initial treatment (MAIT), complete elimination of cogongrass shoot and rhizome biomass and 100% visual control was achieved in several herbicide treatment–timing combinations at both locations. These included glyphosate plus imazapyr at any application timing, imazapyr in August or October, and glyphosate applied in May and October each year. TNC levels of surviving healthy rhizomes were not affected by herbicide treatments, but a seasonal pattern was observed. The maximum live-rhizome depth was not influenced by any treatment, indicating that herbicides were not preferentially leaving deeper, surviving rhizomes. These results demonstrate, for the first time, that the entire rhizome layer of cogongrass can be eliminated within 3 yr with multiple treatment options and that cogongrass patch eradication is possible for many land managers. Nomenclature: Glyphosate, glyphosate plus imazapyr, imazapyr, cogongrass, Imperata cylindrica (L.) Beauv. IMPCY. Management Implications: Cogongrass is one of the most difficult weeds to manage because of its aggressive growth and persistent rhizomes, which often survive initial herbicide treatments. Historically, research efforts have been focused on cogongrass control, but no published studies have tested strategies for eradication. The present study is the first documented research to demonstrate complete elimination of cogongrass in 18 to 36 mo using repeated, annual herbicide applications. Treatments included glyphosate, imazapyr, and a tank-mix of both applied in the spring, summer, or fall for 3 consecutive yr. Verification of eradication was based on a highly rigid criterion involving measurements of cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content over 3 yr. Cogongrass response to treatments varied by location. By 36 mo after initial treatment, the glyphosate plus imazapyr treatment applied at any timing, the imazapyr treatment applied in August or October, and the glyphosate treatment applied in May and October each year resulted in complete elimination of cogongrass shoot and rhizome biomass. The maximum live-rhizome depth (16 cm ± 2 SE) was not influenced by any treatment. During the 3-yr period, herbicides did not affect TNC levels of surviving rhizomes, indicating that repeated treatments directly killed rhizomes, rather than slowly exhausting energy reserves. We are not suggesting that cogongrass can be eradicated from the southeastern United States; however, with repeated glyphosate or imazapyr herbicide treatments, land managers do have a feasible means of eradicating cogongrass patches.

Triclopyr Application Timing and Concentration Influence Low-Volume Basal Bark Efficacy on Chinese Privet (Ligustrum sinense)

Chinese privet is an invasive shrub that commonly infests roadsides and bottomland forests across the southeastern United States. Its aggressive growth and ability to prolifically sprout from the root collar and shallow lateral roots makes control very difficult. Individual plant treatment methods such as low-volume basal bark herbicide application with triclopyr are commonly used for Chinese privet control. However, little research has been done to examine optimal triclopyr concentrations and application timings for the low-volume basal bark method. Furthermore, little is known regarding basal bark treatment efficacy when plant size varies. To address these questions, field studies were conducted from 2009 to 2011 at two locations in east-central Alabama near Auburn and Opelika. The triclopyr butoxyethyl ester formulation was applied in January or March to Chinese privet shrubs across a range of sizes in a commercially available basal oil carrier at 24 (5% v/v−1), 48 (10% v/v−1), and 96 g L−1 (20% v/v−1). Additionally, a triclopyr butoxyethyl ester ready-to-use formulation (90 g L−1) was applied at 100% v/v−1. Canopy defoliation, sprout height, and mortality were quantified at 6, 12, and 18 mo after treatment. Triclopyr at all concentrations was highly effective in defoliating Chinese privet and reducing height of new basal sprouts. However, mortality was concentration dependent. The 90 and 96 g L−1 treatments resulted in 88 and 89% mortality across timings, while the 24 and 48 g L−1 treatments resulted in 63 and 76% mortality. March applications were less effective as basal diameter increased, especially at the lower triclopyr concentrations where mortality fell to less than 40%. These results indicate that triclopyr is an effective treatment for Chinese privet control, but efficacy is influenced by concentration, application timing, and plant size. Nomenclature: Triclopyr; Chinese privet, Ligustrum sinense Lour. Management Implications: Chinese privet is an aggressive shrub that is especially problematic in bottomland hardwood areas of the southeastern United States. Many land managers use individual plant treatment (IPT) methods to control Chinese privet in these areas to improve selectivity and reduce non-target damage. However, little has been published regarding IPT methods for Chinese privet control. We examined basal bark treatment with triclopyr across a range of concentrations as a method for controlling Chinese privet at January and March timings. In general, we found that winter (January) applications of triclopyr from 24 to 96 g L−1 resulted in greater than 90% defoliation while applications of 48 to 96 g L−1 achieved greater than 80% mortality. Early spring (March) applications of 24 to 96 g L−1 resulted in greater than 80% defoliation. However, application concentrations of 90 to 96 g L−1 were required to achieve 80% mortality. These results demonstrate that winter applications of triclopyr as a low-volume basal bark treatment may be effective at lower concentrations than the commercial standard of 96 g L−1. However, March applications will likely require either the 90 or 96 g L−1 concentration for successful control.

The Influence of Treatment Timing and Shrub Size on Chinese Privet ( Ligustrum sinense ) Control with Cut Stump Herbicide Treatments in the Southeastern United States

Abstract Since its introduction to the United States in 1852, Chinese privet (Ligustrum sinense Lour.) has spread throughout the Southeast, invading many natural areas. Manual control by cutting or shredding is one of the most common strategies many land managers employ. However, rapid sprouting from the root collar and lateral roots commonly results in poor control. Cutting followed by either glyphosate or triclopyr application to the stumps is generally effective, but the efficacy of these herbicides in relation to treatment timing and L. sinense root collar diameter has not been evaluated. The objective of this experiment was to determine the effectiveness of glyphosate and triclopyr cut stump treatments compared with cutting alone at spring and fall timings across a range of L. sinense size classes. Studies were conducted at two locations in Auburn, AL. Treatments included cut stump + no herbicide, cut stump+ glyphosate (120 g L-1), or cut stump + triclopyr (90 g L-1). Treatments were applied to at least 50 experimental units each at April and November timings. Root collar diameter was recorded for each stem, stems were cut 2.5 cm above the ground, and herbicide treatments were applied within 30 s. Ligustrum sinense mortality and sprouting were quantified 6, 12, and 18 mo after treatment. Both glyphosate and triclopyr amine were very effective in controlling L. sinense at both spring and fall timings. However, glyphosate provided slightly better results than triclopyr when lateral sprouting was included. Application timing also was significant, with a lower percentage of sprouting following November treatments than April treatments. Stem size influenced treatment success, as larger stumps tended to sprout more than smaller stumps. These results indicate L. sinense can be controlled with cut stump herbicide treatment using either glyphosate or triclopyr with spring or fall timings at concentrations much lower than typically used.

Response of Twelve Florida Cogongrass (Imperata cylindrica) Populations to Herbicide Treatment

Abstract Cogongrass [Imperata cylindrica (L.) Beauv.] is an invasive grass in the southeastern United States, and its impacts strongly affect the region, especially Florida. Herbicide strategies have been limited to glyphosate in natural areas and imazapyr in managed pine forests and non-crop areas where its soil residual activity is of less concern. This lack of options has raised concern for herbicide resistance, which has never been documented for I. cylindrica. Land managers have also reported variable I. cylindrica control, especially with glyphosate. To determine whether herbicide resistance was a possible explanation, we examined glyphosate response of I. cylindrica from 12 Florida populations. We also tested aminocyclopyrachlor with and without glyphosate and flumioxazin with glyphosate. Results indicated that herbicide performance was similar across I. cylindrica populations: glyphosate and aminocyclopyrachlor reduced I. cylindrica biomass by 78% and 76%, respectively, and the combined tank mix reduced cogongrass biomass by 91%. Flumioxazin tank mixed with glyphosate did not improve control compared with glyphosate alone. There were no differences in pretreatment I. cylindrica shoot height, with the exception of two panhandle populations that were shorter. Subsequent harvests indicated few differences in shoot and root plus rhizome weights among untreated controls for almost all populations, with the exception of one of the initially shorter panhandle populations. Our findings indicate that variability in glyphosate efficacy, as suggested by managers, is unlikely due to any conferred resistance. Other abiotic factors such as drought and shade and applicator factors such as carrier water quality should be examined to better understand this issue. Additional studies examining non-target impacts of aminocyclopyrachlor should be conducted to determine its potential fit into I. cylindrica management.