Dwight K. Lauer

Comparison of Aminocyclopyrachlor to Common Herbicides for Kudzu (Pueraria montana) Management

Abstract Kudzu is an invasive perennial climbing vine characterized by fast growth rates and tolerance to control measures. Repeated applications with high rates of 2,4-D plus picloram provide effective kudzu control, but picloram use is not permitted in certain states due to groundwater pollution concerns. Studies were conducted in Alabama and Florida to compare kudzu control with aminocyclopyrachlor, a new herbicide, to control provided by aminopyralid, clopyralid, metsulfuron methyl, and picloram plus 2,4-D, which are common treatments for kudzu management. Two annual applications of the same herbicide treatment were evaluated for effects on kudzu cover, kudzu volume index, and cover of other vegetation. Aminocyclopyrachlor at 140 to 280 g ae ha−1 (2 to 4 oz ae ac−1) was as effective as the standard 4.48 kg ae ha−1 (4 lb ae ac−1) 2,4-D amine plus 1.2 kg ae ha−1 picloram for kudzu control. There were no differences in kudzu control among the three rates of aminocyclopyrachlor tested. Colonization by graminoids, forbs, and Rubus spp. at 2 yr was greatest for herbicides providing the best kudzu control: aminocyclopyrachlor, and 2,4-D plus picloram. Herbicide treatments were more effective in controlling kudzu at the Alabama location, but repeated annual applications for 2 yr did not completely eliminate kudzu with any treatment at either site. Nomenclature: 2,4-D; aminocyclopyrachlor; aminopyralid; clopyralid; metsulfuron methyl; picloram; kudzu, Pueraria montana (Lour.) Merr., USDA code PUMOL, EPPO code PUELO. Interpretive Summary: The new herbicide, aminocyclopyrachlor, applied at 140 to 280 g ae ha−1 controlled kudzu as well as the standard treatment for kudzu management, 4.48 kg ae 2,4-D amine plus 1.21 kg ae picloram, and generally better than the other common kudzu herbicides metsulfuron methyl, aminopyralid, and clopyralid. Graminoids, Rubus spp., and forbs recolonized plots receiving the most effective treatments for kudzu control. Graminoid (grasses, sedges) cover increased following aminocyclopyrachlor treatments, an important consideration for restoration of infestations where kudzu was planted for erosion control in the region. Annual herbicide applications for 2 yr did not eradicate kudzu, confirming the need for multiple years of treatment or more frequent applications.

Two-year development of southern pine seedlings and associated vegetation following spray-and-burn site preparation with imazapyr alone or in mixture with other herbicides

Eight herbicide combinations containing imazapyr alone or in mixture with glyphosate, triclopyr, or picloram+2,4-D were applied July–August 1991 at each of three upland sites in the southeastern U.S., with or without a subsequent broadcast burn in September. Seedlings of loblolly (Pinus taeda L.) or slash (P. elliottii Engelm. var. elliottii) pine were planted that winter. Second-year (August 1993) vegetation responses indicate that broadcast burning, in combination with herbicides, was associated with increased abundances of grasses, forbs, and shrubs and decreased abundances of vines and hardwood trees. In the presence of burning, imazapyr-in-mixture treatments were associated with a high abundance of grass (53% cover) and a mean size of pines less than that of seedlings growing in imazapyr-alone treatments. In the absence of burning, imazapyr-alone treatments were associated with a high abundance of blackberry (21% cover), an average height of hardwoods (131 cm) exceeding that of pines (71 cm), and a mean size of pines less than that of trees growing in imazapyr-in-mixture treatments. Hardwood height in the absence of burning was less when imazapyr was combined with glyphosate (75 cm) than with triclopyr (102 cm). Regardless of the presence or absence of burning, size of pines and abundance of shrubs and hardwoods did not differ between imazapyr rates of 0.56 and 0.84 kg acid equivalent/ha or among herbicides applied in mixture with imazapyr.

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.

Macartney Rose (Rosa bracteata) Response to Herbicide and Mowing Treatments

Abstract Macartney rose is an aggressive thorny shrub that displaces forage species and hinders cattle grazing in rangelands and pastures of the southern United States. Historically, Macartney rose has proven to be extremely difficult to control even with high rates of soil residual herbicides such as picloram. Recent advances in herbicide chemistry warrant testing on this troublesome species. We compared mowing and late summer broadcast applications of thirteen herbicide treatments that included combinations of aminopyralid, fluroxypyr, metsulfuron, picloram, triclopyr, and 2,4-D. Treatments were applied to the same rose clumps for 2 consecutive yr. An additional mowing was done to one half of the rose clumps in each treatment 6 mo after the second herbicide treatment. At 11 mo after initial treatment (MAIT), mowing and all herbicide treatments performed very poorly and provided 35% control or less. At 12 mo after retreatment (24 MAIT), picloram + 2,4-D and aminopyralid + metsulfuron, both followed by mowing, were the most effective treatments, providing 72 to 91% control. All other treatments provided less than 70% control. However, complete clump mortality was very low across all treatments, ranging from 3 to 32%. These results indicate that Macartney rose suppression is possible with certain new herbicides, but complete clump kill is still lacking. Nomenclature: Aminopyralid, fluroxypyr, metsulfuron, picloram, triclopyr, 2,4-D, Macartney rose, Rosa bracteata J. C. Wendl. ROSBC Management Implications: Macartney rose is one of the most difficult-to-control thorny shrubs in pastures across the Southeast. We evaluated a suite of newer pasture herbicides that included several combinations of 2,4-D, aminopyralid, fluroxypyr, metsulfuron, picloram, and triclopyr. Broadcast treatments were applied for 2 consecutive yr in August over the same individual rose clumps and mowing was done 6 mo after the second application. We found that none of the herbicides and rates tested effectively killed entire clumps but that Macartney rose was suppressed best with picloram + 2,4-D treatments. Triclopyr was ineffective when applied alone or when tank-mixed with aminopyralid + 2,4-D or aminopyralid + metsulfuron. Metsulfuron was also ineffective and did not improve control when applied with aminopyralid alone or in combination with 2,4-D. These results indicate that typical annual broadcast applications currently utilized for broadleaf pasture weed control will not effectively eliminate the invasive shrub Macartney rose and more integrated methods need to be evaluated.

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.

Seasonal Variation in Macartney Rose (Rosa bracteata) Response to Herbicide Treatment

Macartney rose is an aggressive, thorny shrub that suppresses forage production and strongly hinders cattle grazing in southern pastures. Previous studies have found this weed to be extremely difficult to control with most pasture herbicides. We conducted two studies in central Alabama to assess several new herbicide chemistries applied at spring, early fall, and late fall timings. In the first study, we compared aminocyclopyrachlor, tank mixed with either 2,4-D, triclopyr, metsulfuron, or chlorsulfuron, with the commercial standard, picloram + 2,4-D. In the second study, we compared aminopyralid, tank mixed with either 2,4-D or metsulfuron and triclopyr + fluroxypyr, to the commercial standard, picloram + 2,4-D. Aminocyclopyrachlor + chlorsulfuron or metsulfuron and aminopyralid + 2,4-D or metsulfuron provided acceptable control and were comparable to picloram + 2,4-D at the early fall timing. Macartney rose control with treatments applied at the late fall timing tended to be less than commercially acceptable levels. We found that no herbicide treatment controlled Macartney rose at the spring timing. In addition, triclopyr + fluroxypyr did not control Macartney rose at any application timing. These results indicate that the early fall timing was optimal and that both aminocyclopyrachlor and aminopyralid can provide good Macartney rose control when mixed with certain other herbicides, including metsulfuron. Nomenclature: 2,4-D; aminocyclopyrachlor; aminopyralid; chlorsulfuron; fluroxypyr; metsulfuron; picloram; triclopyr; Macartney rose, Rosa bracteata J.C. Wendl ROSBC. Rosa bracteata es un arbusto espinoso agresivo que suprime la producción de forrajes e inhibe fuertemente el pastoreo del ganado en pastizales del sur. Estudios previos han encontrado que esta maleza es extremadamente difícil de controlar con la mayoría de los herbicidas para pastos. Nosotros realizamos dos estudios en el centro de Alabama para evaluar varios herbicidas químicos nuevos, aplicados en la primavera, temprano en el otoño, y tarde en el otoño. En el primer estudio, comparamos con el estándar comercial, picloram + 2,4-D aplicaciones de aminocyclopyrachlor, mezclado ya fuese con 2,4-D, triclopyr, metsulfuron, o chlorsulfuron. En el segundo estudio, comparamos aminopyralid, mezclado en tanque con ya fuese 2,4-D o metsulfuron y triclopyr + fluroxypyr, con el estándar comercial, picloram + 2,4-D. Aminocyclopyrachlor + chlorsulfuron o metsulfuron y aminopyralid + 2,4-D o metsulfuron brindaron un control aceptable y fueron comparables con picloram + 2,4-D para aplicaciones temprano en el otoño. El control de R. bracteata con tratamientos aplicados tarde en el otoño tendió a ser inferior a los niveles comercialmente aceptables. Encontramos que ningún tratamiento con aplicaciones de herbicidas en la primavera controló R. bracteata. Adicionalmente, triclopyr + fluroxypyr no controló R. bracteata en ningún momento de aplicación. Estos resultados indican que temprano en el otoño fue el momento de aplicación óptimo y que tanto aminocyclopyrachlor como aminopyralid pueden brindar buen control de R. bracteata cuando se mezclan con otros herbicidas incluyendo metsulfuron.

Japanese Climbing Fern (Lygodium japonicum) Management in Florida's Apalachicola Bottomland Hardwood Forests

Abstract Japanese climbing fern (Lygodium japonicum) is an invasive vine that has been identified as an economic and ecological threat in forest ecosystems of the Southeast. In two separate studies, we examined the use of directed sprays of glyphosate, imazapyr, and metsulfuron-methyl herbicides, alone and in combination, for control of Japanese climbing fern and for impacts to associated vegetation in mixed bottomland hardwood–cypress forests at two first terrace sites of the Apalachicola River in north Florida. Two yr after treatment, various rates of glyphosate alone generally provided greater percent control (84 to 95%) than imazapyr alone (−25 to 86%) or metsulfuron-methyl alone (−5 to 53%). Combinations of 2% glyphosate and imazapyr and/or metsulfuron-methyl resulted in 81 to 97% control at 2 yr after treatment, with no significant differences among the combination treatments or 2% glyphosate alone. Change in percent cover of associated vegetation groups was not influenced by treatment except for one location where graminoid cover increased 1 yr after metsulfuron-methyl treatment but decreased after imazapyr or glyphosate application. Species richness of dominant understory vegetation remained nearly constant at both locations regardless of treatment. These data indicate that glyphosate alone or in combination with imazapyr or metsulfuron-methyl will provide effective, although not complete, control of Japanese climbing fern, and that directed herbicide sprays minimally impact nontarget vegetation. Nomenclature: