Megathyrsus maximus is nonnative in the neotropics, with a tall form that is commonly used as a forage grass and a smaller-statured form that is considered invasive in south Texas, USA. Biological control researchers are challenged to find an agent that will attack the short form, but not the desirable tall form in other parts of the neotropics. We conducted molecular analyses on 155 Megathyrsus maximus samples from its native range in Africa and compared them with U.S. short-form samples to help determine the geographic origins of its invasion. We found eight distinct genotypes in 34 short-form samples from Texas and Florida, USA. The highest genetic similarity of invasive samples was with plants from South Africa, while highest matches for the desirable tall form were from Kenya, Uganda, Ivory Coast, and Zambia. Ongoing biological control agent exploration and research has found agents from Kenya that are associated with an M. maximus genotype not well matched to the invasive short form, thus leading to a lack of rearing success. Two eriophyoid mite agents from the genetic match locality in South Africa have been evaluated but are not sufficiently host specific, as they develop on both the short and tall forms. Additional exploration is needed at the genetic match populations in South Africa to discover and evaluate potential biological control agents for the invasive form of M. maximus.

The invasive vine black swallowwort [Vincetoxicum nigrum (L.) Moench = Cynanchum louiseae Kartesz & Gandhi, Apocynaceae] is difficult to control, and herbicide studies are lacking. This long-lived perennial species is primarily found in high-light environments in natural areas and perennial cropping systems in northeastern North America. We conducted a 3-yr herbicide efficacy study, with or without mowing, in an old-field site infested with V. nigrum in Dutchess County, NY, USA. Experimental plots were either herbicide treated in early July or mowed in early July and subsequently herbicide treated in late August for 2 yr with the potassium salt of glyphosate (2.02 kg ae ha−1), the isopropylamine salt of glyphosate (1.35 kg ae ha−1), or the butoxyethyl ester of triclopyr (1.79 kg ae ha−1). Both glyphosate formulations were effective in reducing V. nigrum aboveground biomass, although they were somewhat less effective in reducing cover or stem densities of V. nigrum plants >10-cm tall after 2 yr compared with untreated plots. Mowing did not always enhance the efficacy of foliar glyphosate applications. Triclopyr, with or without mowing, was generally not effective against V. nigrum in our study. The only significant effect of triclopyr was to increase the cover of grasses in the plots. While annual applications of glyphosate can be useful for management of V. nigrum infestations, higher rates and more frequent applications of triclopyr need to be investigated to determine its usefulness for V. nigrum control.

Garlic mustard [Alliaria petiolata (M. Bieb.) Cavara & Grande] is an invasive Brassicaceae species native to Europe. As obligate biennials, A. petiolata rosettes require a sufficient length of cold during the winter to flower the following spring. As such, mild winter temperatures could limit the species’ potential western and southern distribution in North America. The goal of this research was to characterize the vernalization period required for A. petiolata rosettes to develop the capacity to flower. The objectives of this research were: (1) confirm whether A. petiolata rosettes required a vernalization period to flower; (2) define base and upper temperatures that satisfy the vernalization requirement of A. petiolata rosettes under field conditions; (3) determine the vernalization requirement for flowering and calculate chilling degree days (CDD) accumulated during the cold period; and (4) in a common garden, determine the vernalization requirement of A. petiolata rosettes collected from the southern and northern ranges of its distribution in North America and Europe. The probability of flowering increases as A. petiolata rosettes accumulate CDD. This relationship is defined by a binary logistic (logit) function, with base and maximum temperatures of −3 and 4 C, respectively. The regression equation model predicted that 68 and 120 CDD would result in 50% and 99% probability of flowering, respectively, across all locations. Rosettes from five different seed sources varied in the CDD required for flowering when grown in a common garden. Rosettes originating from a Croatia seed source flowered after exposure to fewer CDD than those from Scotland. In North America, rosettes originating from seeds from Arkansas were more likely to flower after exposure to fewer CDD than those from Ohio or Minnesota. Our results may be used to predict the potential distribution of A. petiolata in North America.

Asiatic dayflower (Commelina communis L.) is becoming increasingly invasive in Christmas tree plantations in the U.S. Northeast. Response of C. communis to preemergence or postemergence herbicides was evaluated in separate field and greenhouse experiments. The preemergence herbicides consisted of two application rates of flumioxazin (215 and 429 g ai ha−1), hexazinone plus sulfometuron-methyl (316 and 527 g ai ha−1), indaziflam (41 and 82 g ai ha−1), and S-metolachlor (2,136 and 4,272 g ai ha−1). The postemergence herbicides were: bentazon at 1,121 g ai ha−1, clopyralid at 280 g ae ha−1, mesotrione at 526 g ai ha−1, topramezone at 294 g ai ha−1, and triclopyr at 842 g ae ha−1. At 16 wk after treatment, higher rates of flumioxazin (429 g ha−1), hexazinone plus sulfometuron-methyl (527 g ha−1), indaziflam (82 g ha−1), and S-metolachlor (4,272 ha−1) provided 80% to 92% control and reduced C. communis plant density by 84% to 93% compared with the nontreated control. The lower rates of flumioxazin (215 g ha−1), hexazinone plus sulfometuron-methyl (316 g ha−1), and S-metolachlor (2,136 ha−1) gave 65% to 72% control and reduced C. communis plant density by 27% to 75% compared with the nontreated control. The postemergence application of mesotrione at 526 g ha−1, topramezone at 294 g ha−1, and triclopyr at 842 g ha−1 resulted in 76% to 90% control and reduction in dry biomass of 10- to 12-leaf C. communis at 28 d after treatment. Bentazon at 1,121 g ha−1 and clopyralid at 280 g ha−1 applied postemergence were ineffective with <10% control and reduction in C. communis dry biomass. This study showed that C. communis can be managed effectively with currently registered preemergence and postemergence herbicides in Christmas trees.

Hybridization can play an important role in the evolution of invasiveness. Eurasian watermilfoil (Myriophyllum spicatum L.) is a widespread aquatic invasive plant species that hybridizes with native northern watermilfoil (Myriophyllum sibiricum Kom.). Previous studies have found mixed evidence for whether hybrid watermilfoil (Myriophyllum spicatum × sibiricum) and pure M. spicatum differ in vegetative growth rate and herbicide response. While several studies have emphasized variation in these traits among M. spicatum × sibiricum genotypes, variation within M. spicatum has not been considered. Therefore, it is unclear how much genetic variation influences invasive traits and management outcomes within M. spicatum versus between M. spicatum and M. spicatum × sibiricum. If M. spicatum × sibiricum genotypes are always more invasive than M. spicatum genotypes, simply distinguishing taxa may be sufficient for identifying lake management priorities; however, if significant phenotypic overlap is observed between taxa, distinguishing individual genotypes may be important for tailoring management strategies. We performed replicated trials of a vegetative growth and 2,4-D assay to measure clonal variation in growth rate and herbicide response of M. spicatum and M. spicatum × sibiricum. Our results indicate that M. spicatum × sibiricum exhibits higher average vegetative growth than M. spicatum, regardless of whether it was treated with subsurface applications of 2,4-D. We did not observe interactions between taxon and treatment or between genotype and treatment. Despite differences between M. spicatum and M. spicatum × sibiricum in average vegetative growth, there was substantial overlap between taxa. For example, we found that the fastest-growing genotype of pure M. spicatum did not differ significantly in average growth from the fastest-growing M. spicatum × sibiricum genotype. The potential for overlap between these invasive Myriophyllum taxa suggests that distinguishing and characterizing genotypes may be more informative for management than simply distinguishing between M. spicatum and M. spicatum × sibiricum.

Several Miscanthus species are cultivated in the U.S. Midwest and Northeast, and feral populations can displace the native plant community and potentially negatively affect ecosystem processes. The monetary cost of eradicating feral Miscanthus populations is unknown, but quantifying eradication costs will inform decisions on whether eradication is a feasible goal and should be considered when totaling the economic damage of invasive species. We managed experimental populations of eulaliagrass (Miscanthus sinensis Andersson) and the giant Miscanthus hybrid (Miscanthus × giganteus J.M. Greef & Deuter ex Hodkinson & Renvoize) in three floodplain forest and three old field sites in central Illinois with the goal of eradication. We recorded the time invested in eradication efforts and tracked survival of Miscanthus plants over a 5-yr period, then estimated the costs associated with eradicating these Miscanthus populations. Finally, we used these estimates to predict the total monetary costs of eradicating existing M. sinensis populations reported on EDDMapS. Miscanthus populations in the old field sites were harder to eradicate, resulting in an average of 290% greater estimated eradication costs compared with the floodplain forest sites. However, the cost and time needed to eradicate Miscanthus populations were similar between Miscanthus species. On-site eradication costs ranged from $390 to $3,316 per site (or $1.3 to $11 m−2) in the old field sites, compared with only $85 to $547 (or $0.92 to $1.82 m−2) to eradicate populations within the floodplain forests, with labor comprising the largest share of these costs. Using our M. sinensis eradication cost estimates in Illinois, we predict that the potential costs to eradicate populations reported on EDDMapS would range from $10 to $37 million, with a median predicted cost of $22 million. The monetary costs of eradicating feral Miscanthus populations should be weighed against the benefits of cultivating these species to provide a comprehensive picture of the relative costs and benefits of adding these species to our landscapes.

Downy brome (Bromus tectorum L.) is a highly invasive winter annual grass that can fill open niches in native plant communities. Prescribed burning is often used to control B. tectorum and can be combined with herbicide treatments to extend the duration of control and promote the native plant community. Several herbicides have been evaluated in conjunction with burning for B. tectorum control, although the herbicide indaziflam has not. In September 2017, two B. tectorum–infested sites were burned in Colorado foothill shrublands. In March 2018, indaziflam was applied alone or in combination with glyphosate, rimsulfuron, or imazapic. These treatments were compared with imazapic plus glyphosate as a standard. All treatments were made within burned and non-burned areas in a crossed-nested design. Bromus tectorum cover and the desirable plant community responses were evaluated 1 and 2 yr after treatment (YAT). In non-burned areas, all indaziflam treatments reduced B. tectorum cover compared with the control. In contrast, reductions from the imazapic treatments did not persist after the first year. Most post-burn treatments further decreased B. tectorum cover compared with the non-burned treatments. The most effective treatments (indaziflam 44 and 73 g ai ha−1 + imazapic 123 g ae ha−1) provided similar levels of control (<1% B. tectorum cover at 2 YAT), with or without burning. Desirable plant cover, richness, and diversity were not negatively impacted by burning or herbicide treatments. Plant diversity and species richness increased at Site 2 when burning was followed by indaziflam treatments. This study indicates that B. tectorum control using indaziflam can be enhanced when applied after burning, and the combinations with imazapic or rimsulfuron provide a wider application window compared with the combination with glyphosate.

Invasive woody perennials pose an immense threat to the diversity and function of many ecosystems, including forests in the eastern United States. While herbicide treatments have proven effective in controlling many plant invasions, there is considerable interest in the refinement of herbicide prescriptions to improve efficacy and prevent non-target damage. Adjuvants are widely utilized to improve herbicide efficacy, but research on novel adjuvants is often lacking. Furthermore, adjuvant research has generally focused on enhancement of foliar herbicide absorption, and few studies focus on adjuvant utility for other herbicide delivery techniques such as cut stump treatments. We evaluated 2XL—a cocktail of cellulase enzymes derived from fungi—as a potential herbicide adjuvant for use with glyphosate applied in a cut stump treatment due to its ability to degrade a key component of cell walls. We conducted a field experiment using the cut stump method of treatment (cut surface treated with herbicide) on a problematic invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Herder]. We tested combinations of three concentrations of 2XL with five concentrations of glyphosate and hypothesized that low concentrations of glyphosate combined with 2XL would be as effective in limiting the resprouting of L. maackii as higher concentrations of glyphosate without the enzymes. Our results indicated that 2XL did not improve glyphosate efficacy for reducing the number of resprouting stems or the length of the longest resprouting stem within the same or following year as treatment. Limited data indicated the combination of 2XL and glyphosate applied at 30 g L−1 slightly increased resprouting in the year following treatment. While 2XL did not improve glyphosate efficacy, our results showed effective control of L. maackii at the lowest concentration of glyphosate tested (30 g L−1), suggesting that concentrations lower than those typically applied may be effective in controlling L. maackii within parameters similar to those tested here.

Invasive plants in the riparian zone can negatively affect the characteristics and quality of a watershed. To support the development of a watershed management plan and foster public appreciation of the value of the riparian zone, Mohonk Preserve established a volunteer monitoring program surveying sites for invasive species. Between 2017 and 2019, citizen scientists repeatedly surveyed 20 sites in the Hudson River Valley in New York for 10 invasive plant species: purple loosestrife (Lythrum salicaria L.), common reed [Phragmites australis (Cav.) Trin. ex Steud], multiflora rose (Rosa multiflora Thunb.), garlic mustard [Alliaria petiolata (M. Bieb.) Cavara & Grande], dame’s rocket (Hesperis matronalis L.), Japanese knotweed (Polygonum cuspidatum Siebold & Zucc.), wineberry (Rubus phoenicolasius Maxim.), barberry (Berberis spp.), Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], and Asiatic bittersweet (oriental bittersweet, Celastrus orbiculatus Thunb.). We found that the number of target species detected was higher on sites closer to paved roads and with increasing drainage area size, while lower with higher percentages of forested land in the basin. Our analysis results highlight variation in the presence of target invasive species across the Hudson River Valley region, highlighting sites and areas to monitor for future introductions and take action to prevent species’ invasions. Our results highlight differences in the most relevant abiotic factors for hydrophytes and non-hydrophyte species, underscoring the importance of considering species’ life-history traits before the development of management plans for invasive plant species in the riparian zone. Our case study of community-collected data in the Hudson River Valley region using a relatively simple monitoring protocol can provide a road map for other regions fostering volunteer engagement with invasive plants.

The invasive annual grass downy brome (Bromus tectorum L.) is a critical threat to the semiarid shrublands that characterize western North America. More abundant fine fuel after invasion typically increases fire frequency in plant communities adapted to relatively infrequent burning, reducing the likelihood of native plant persistence. Currently, imazapic is most often used to manage B. tectorum, but reinvasion from the seedbank after treatment is common. Indaziflam is a newer herbicide recently labeled for use in rangelands grazed by livestock, and many research trials have demonstrated its ability to deplete invasive annual grass seedbanks. We evaluated the effectiveness of indaziflam and imazapic for reducing B. tectorum density and cover over a period of approximately 5 yr (57 mo after treatment [MAT]) at two invaded sagebrush-grassland sites near Pinedale, WY. Treatments included three different indaziflam rates (51, 73, and 102 g ai ha−1) and one imazapic rate (123 g ai ha−1), and these treatments were reapplied to half of each plot at 45 MAT to evaluate the effects of two sequential applications. We also measured perennial grass cover, because positive perennial grass responses were observed after release from B. tectorum competition in other studies, and perennial grasses may provide resistance to B. tectorum reinvasion. Intermediate and high indaziflam rates (73 and 102 g ha−1, respectively) reduced B. tectorum cover and density at 45 MAT, and perennial grass cover responded positively to some treatments, mostly early in the study (≤33 MAT). Imazapic reduced B. tectorum initially, but did not affect density or cover at either site beyond 21 MAT. Reapplication did not substantially improve B. tectorum control at 57 MAT in plots treated with intermediate and high indaziflam rates, suggesting that long-term control with a single indaziflam treatment may be possible in some cases.

Yellow toadflax (Linaria vulgaris Mill.; Scrophulariaceae) is an invasive herbaceous perennial weed of agricultural and natural habitats throughout North America. In pastures or native rangelands, use of biological control is an attractive option, particularly if the agent can be established quickly. Rhinusa pilosa (Gyllenhal) (Coleoptera: Curculionidae), a stem-galling weevil, was first released in Canada in 2014 to evaluate its potential to control L. vulgaris. Rhinusa pilosa requires young, vigorously growing shoots to establish. Ability to estimate when adequate shoots will be available could inform release timing, thus improving establishment success. There is currently no growing degree-day (GDD) model for L. vulgaris. Our main objective was to develop a GDD model for the emergence of L. vulgaris shoots and discuss the utility of such a model in relation to the establishment of R. pilosa in Nova Scotia. Four sites containing five randomly placed 1-m2 quadrats were monitored for the emergence of L. vulgaris shoots twice weekly in spring to summer 2017 and 2018 by recording number of shoots and shoots with flower buds. A GDD (Tbase 2 C) model for shoot emergence of L. vulgaris was developed and validated using independent shoot emergence data. Shoots emerged in the spring between 124 and 244 GDD with 90% of all shoots emerged between 681 and 1,117 GDD. Model estimation for the initiation of shoot emergence was 74 GDD, with 10%, 50%, and 90% shoot emergence estimated to occur at 179, 409, and 811 GDD, respectively. Rhinusa pilosa adults were released in 2016 (three sites) and 2017 (one site), and number of shoots with galls was recorded. Galls were observed in all three sites in 2016 and in three of the four sites in 2017, with none found in 2018. Timing of release and soil moisture are discussed as factors affecting establishment of R. pilosa in Nova Scotia.

Invasive plant species (IPS) management in national parks is a complex problem often characterized by the involvement of various organizations with different responsibilities, legal mandates, and jurisdictions. These institutional arrangements shape the structure, function, and decision-making behaviors of organizations and influence management effectiveness. Drawing on institutional theory, this study analyzed institutional arrangements and how these influenced IPS management in Vietnam’s national parks. Data were collected between May and July 2017 using in-depth interviews with 39 key informants with responsibility for IPS management at different institutional levels (national, provincial, and local national parks). Results demonstrated that IPS management in Vietnam’s national parks was characterized by centralized management with overlaps and gaps in vertical institutional relationships that limited the effectiveness of horizontal relationships. These characteristics resulted in a lack of clear guiding regulations and limited resources that restricted decision making and hindered implementation at the local national park level. The study highlights the need for a common set of principles across agencies, governed by an overarching body to promote constructive relationships across the vertical and horizontal institutional dimensions of IPS management.

Invasive aquatic plants constantly threaten freshwaters and associated environs globally. Water resource managers frequently seek new control tactics to combat invasive macrophytes, especially when the availability of herbicides registered for submersed plant control is limited. The synthetic auxin herbicide, florpyrauxifen-benzyl, recently registered (2018) for aquatic site applications in the United States, has shown success in controlling several invasive aquatic weeds. Studies were conducted to evaluate responses of native and invasive submersed plants to florpyrauxifen-benzyl under growth chamber conditions to provide insight on the selectivity of varying herbicide concentrations in New Zealand. Florpyrauxifen-benzyl concentrations evaluated ranged from 0.01 to 107.86 µg ai L−1, encompassing the maximum use concentration (48 µg L−1) for submersed plant applications. Dose–response metrics indicated the New Zealand native species watermilfoil [Myriophyllum triphyllum Orchard] was highly sensitive to florpyrauxifen-benzyl following a 21-d static exposure, having a dry weight 50% effective concentration (EC50) value of 1.2 µg L−1. The invasive species oxygen-weed [Lagarosiphon major (Ridley) Moss] and Canadian waterweed (Elodea canadensis Michx.) were less sensitive, with dry weight EC50 values of 35.4 and >107.86 µg L−1, respectively. Brazilian waterweed (Egeria densa Planch.) was most tolerant to the tested concentrations, as EC50 values were not achieved. Overall, results indicate florpyrauxifen-benzyl demonstrates potential for controlling L. major, with further large-scale screening required to confirm control among field site applications. As the native species (M. triphyllum) was most sensitive to florpyrauxifen-benzyl compared with the invasive plant evaluated (I/N ratio indicated >31.3 times more sensitive), any targeted concentration used for invasive plant control for field applications would likely injure the native M. triphyllum plants. Future studies should investigate additional native and invasive species for management guidance and consider how exposure times influence plant response using similar florpyrauxifen-benzyl concentrations tested in the present study.

There is limited documentation of cross-tenure collaborative weed management programs, and no consistent set of metrics for evaluating their performance. In this study, 12 weed management practitioners in southeast Australia participated in a qualitative social research project to discuss and document examples of cross-tenure collaborative weed management and critically reflect on whether existing metrics are suitable for evaluating the performance of their programs. Analysis of focus group discussions, project documentation, subsequent reflections, and review of the literature reveal that weed management practitioners, in Australia and elsewhere, mostly rely on metrics that measure weed management inputs, such as herbicides, labor, and costs. Metrics used to evaluate social outcomes focus on benefits for individuals rather than social relationships or achievement of equitable outcomes. Social research on collaborative governance and social science methods more broadly, such as social network analysis and collective narratives, could be used by weed management practitioners to better evaluate and explain social–ecological outcomes over time.

Although it has been demonstrated that environmental changes within a year can affect the reproduction, survival, and growth of invasive species, these factors have rarely been incorporated into demographic analyses. Therefore, we applied multistate demographic models (based on capture–recapture animal methods accounting for imperfect detectability of individuals in natural conditions) to evaluate the effects of reproductive phenology and rainy season on the survival and transition/retrogression rates among stage categories of black elderberry (Sambucus nigra L.)—an invasive tree species widely distributed in temperate forests of Europe and America. In the Abies religiosa temperate forest, Mexico City, a multistate demographic model of S. nigra was built using bimonthly censuses during a year. We selected the best-fitting model according to Akaike’s information criterion adjusted for small sample sizes (AICc). We determined the response of reproductive phenology of S. nigra to the rainy season for 2 yr through repeatability and phenotypic plasticity indexes. Our results showed that the reproductive phenology of S. nigra has a low repeatability index and a high phenotypic plasticity index. We demonstrated that additive and interactive effects of reproductive phenology and rainy season promote changes in survival and transition/retrogression rates among stage categories. During the rainy season, the survival probability of seedlings and transition probability toward the adult category increased. Therefore, our study represents a significant contribution to the knowledge of the demographic dynamics of invasive species on an intra-annual scale.

Sulphur cinquefoil (Potentilla recta L.) is an invasive plant of concern within grasslands in western North America. To better understand the role of native plant communities and soil seedbank in P. recta invasion within grasslands, we conducted two greenhouse studies to examine (1) P. recta growth response when grown with and without fertilizer in established native plant communities of varying functional groups (grasses, forbs, or grasses and forbs), and (2) the prevalence of P. recta and other species in the soil seedbank at varying soil depths (0 to 5 cm, 5 to 10 cm, 10 to 15 cm) of grasslands invaded by P. recta in southeastern British Columbia, Canada. The growth response of P. recta did not differ between the native plant communities. However, P. recta above- and belowground biomass declined as native plant aboveground biomass increased, suggesting a productive plant community may be important to suppress P. recta. Fertilizer did not affect the growth response of P. recta or native plants, suggesting nutrients may not have been a dominant limiting factor under greenhouse conditions. Nine species were identified in the soil seedbank. Seven were nonnative, which included P. recta, and native species represented less than 2% of the seedbank. Of the average number of emerged nonnative seedlings, more than 20% were P. recta. The number of emerged P. recta seedlings was 69% lower at 10- to 15-cm compared with 0- to 5-cm soil depth, although the successful germination of P. recta at greater soil depths suggests viable P. recta seeds are persisting in the seedbank. Active revegetation may be an important strategy to mitigate P. recta reinvasion or secondary invasion by other invasive species from the soil seedbank.

Globally, giant miscanthus (Miscanthus × giganteus J.M. Greef & Deuter ex Hodkinson & Renvoize [sacchariflorus × sinensis]) is used as a biofuel crop due to its ability to persist in a wide range of climates. However, little work has assessed this plant’s ability to invade and persist in wetland habitats. In outdoor mesocosms, we examined M. × giganteus’s ability to grow in simulated wetland versus upland habitats and examined chemical control strategies for both habitats using aquatic-labeled herbicides. Miscanthus × giganteus growth was consistently greater in simulated wetland habitats, with wetland plants 2.4 to 3 times taller than upland plants at 6 wk after treatment (WAT) and 2.8 to 3.3 times taller than upland plants at 12 WAT. Miscanthus × giganteus aboveground biomass was 12.7 to 17.7 times greater in wetland- versus upland-grown plants at 6 WAT and 9.6 to 12.5 times greater at 12 WAT. Belowground biomass was 4.5 to 10.7 times greater in wetland versus upland grown plants at 6 WAT and 4.0 to 6.1 times greater at 12 WAT. Miscanthus × giganteus belowground biomass was always greater than aboveground in both habitats at 6 (6.0 times greater in wetlands and 2.9 times greater in uplands) and 12 WAT (3.8 times greater in wetlands and 1.3 times greater in uplands). Generally, all herbicide treatments reduced M. × giganteus height (66% to 100% reduction) and biomass (84% to 100%) compared with nontreated plants at 12 WAT; however, glyphosate (5,716.3 g ai ha−1) and imazapyr (1,120.8 g ai ha−1) performed better than imazamox (560.4 g ai ha−1) and penoxsulam (98.6 g ai ha−1). This is the first work to provide evidence that M. × giganteus can be chemically controlled in wetland habitats. Furthermore, this is the first work to show that penoxsulam (an acetolactate synthase–inhibiting herbicide) can reduce M. × giganteus growth in upland or wetland habitats.

Tahitian bridal veil [Gibasis pellucida (M. Martens & Galeotti) D.R. Hunt], a Central and South America native plant that is often confused with another more well-known invasive plant, small leaf spiderwort (Tradescantia fluminensis Vell.), has become invasive in natural areas throughout Florida. However, very little is known regarding herbicide control or other methods. To begin the process of developing herbicide recommendations for land managers who are working to control G. pellucida, multiple postemergence herbicides were screened for efficacy in a shaded greenhouse to determine active ingredients and/or combinations that warrant further investigation under field conditions. Nine different herbicides or combinations, including glyphosate, triclopyr acid, 2,4-D + triclopyr, aminopyralid, 2,4-D, triclopyr amine, metsulfuron-methyl, fluroxypyr, and glufosinate, were applied at standard label rates and compared with a nontreated control group. Visual control ratings were taken at 2, 4, and 8 wk after treatment (WAT), and shoot dry weights were determined at trial conclusion (8 WAT). Data showed glufosinate and triclopyr (acid and amine) provided the highest level of control, as evidenced by control ratings (100% or complete control) and shoot fresh weight reduction, followed by 2,4-D + triclopyr (∼70%) and fluroxypyr (∼50% control). Metsulfuron-methyl and 2,4-D provided the lowest level of control, with results similar to those for nontreated plants on most evaluation dates.

Current dam discharge patterns in Noxon Rapids Reservoir reduce concentration and exposure times (CET) of herbicides used for aquatic plant management. Herbicide applications during periods of low dam discharge may increase herbicide CETs and improve efficacy. Applications of rhodamine WT dye were monitored under peak (736 to 765 m3 s−1) and minimum (1.4 to 2.8 m3 s−1) dam discharge patterns to quantify water-exchange processes. Whole-plot dye half-life under minimal discharge was 33 h, a 15-fold increase compared with the dye treatment during peak discharge. Triclopyr concentrations measured during minimum discharge within the treated plot ranged from 214 ± 25 to 1,243 ± 36 µg L−1 from 0 to 48 h after treatment (HAT), respectively. Endothall concentrations measured during minimum discharge in the same plot ranged from 164 ± 78 to 2,195 ± 1,043 µg L−1 from 0 to 48 HAT, respectively. Eurasian watermilfoil (Myriophyllum spicatum L.) occurrence in the treatment plot was 66%, 8%, and 14% during pretreatment, 5 wk after treatment (WAT), and 52 WAT, respectively. Myriophyllum spicatum occurrence in the nontreated plot was 68%, 71%, and 83% during pretreatment, 5 WAT, and 52 WAT, respectively. Curlyleaf pondweed (Potamogeton crispus L.) occurrence in the treatment plot was 29%, 0%, and 97% during pretreatment, 5 WAT, and 52 WAT, respectively. Potamogeton crispus increased from 24% to 83% at 0 WAT to 52 WAT, respectively, in the nontreated plot. Native species richness declined from 3.3 species per point to 2.1 in the treatment plot in the year of treatment but returned to pretreatment numbers by 52 WAT. Native species richness did not change during the study in the nontreated reference plot. Herbicide applications during periods of low flow can increase CETs and improve control, whereas applications during times of high-water flow would shorten CETs and could result in reduced treatment efficacy.