Vallisneria × pseudorosulata S. Fujii & M. Maki is an invasive aquatic weed that has recently become a major issue within the U.S. Southeast. Vallisneria × pseudorosulata is a hybrid between two nonnative eelgrass species (Vallisneria spiralis L. and Vallisneria denseserrulata Makino) and has rapidly overtaken water bodies in Tennessee, Alabama, and Florida. This hybrid can reproduce rapidly through offshoot formation and floating propagules capable of drifting large distances before establishing. Vallisneria × pseudorosulata has been previously found in Japan and is thought to have been introduced in the United States by the aquarium trade or through dumping.

Youngia japonica (L.) DC. was recently discovered on the Azorean island of São Miguel. This species is a cosmopolitan herb that has been reported to be invasive in several regions of the world. It is unclear when and how this plant arrived in São Miguel, Azores. Nevertheless, we hypothesize that this is an unintentional and recent introduction. The populations are expanding in São Miguel, and action is needed to mitigate potential damage to native ecosystems.

Citizen science is becoming very useful in surveying and monitoring biodiversity. Within the European Union LIFE medCLIFFS project, a network of volunteers has been established for the detection and long-term monitoring of invasive plant species that threaten the endemic flora of Mediterranean cliffs in northeastern Spain. Through iNaturalist, volunteers record various data along a series of 1-km transects. Based on the ca. 700 observations collected by volunteers in 2023 (the first year of the project), a simple and visually attractive methodology for assessing the recorded populations has been developed. This method classifies populations into one of three population dynamics categories: (1) propagative behavior (i.e., populations with seedlings or young plants but lacking senescent or dead individuals); (2) senescent behavior (i.e., showing senescent/dead plants but lacking seedlings/juveniles); and (3) a mixed behavior (i.e., containing both). This methodology, whose outputs are easily interpretable as heat maps, allows the collection of large datasets on invasive plants by citizen scientists, with two main purposes: (1) knowing which species are most concerning based on simple, straightforward observations of their population dynamics; and (2) identifying which regions of the study area are more problematic and where management efforts should therefore be directed.

Tree-afflicting pests, such as insects and pathogens, could change forests in ways promoting invasions by non-native plants. After tree death associated with the fungal pathogen oak wilt (Bretziella fagacearum) and its attempted containment (severing root connectivity and sanitation removal of infected trees), we examined change in cover of the non-native liana Oriental bittersweet (Celastrus orbiculatus Thunb.; hereafter Celastrus) at 28 sites in temperate black oak (Quercus velutina Lam.) forests, Ohio, USA. During our 5-yr study spanning 2020 to 2024, Celastrus cover increased significantly (P < 0.05) through time at oak wilt sites but not in untreated reference forest sites without evidence of oak wilt. Celastrus cover increased by an order of magnitude, up to an average of 32 times among oak wilt treatments up to 10 yr old. By 2024, Celastrus cover ranged from 6% to 22% on average in 5- to 10-yr-old oak wilt treatments, compared with 1% cover in reference forest. Results indicate that non-native plant invasion accelerated following disturbance associated with a fungal pathogen and its attempted containment and, more generally, suggest that tree-afflicting pests can promote invasive plants in forests. Co-management of tree-afflicting pests and non-native plants may become increasingly important to ensure forests recovering from tree mortality are dominated by native plants.

Several Elaeagnus species (autumn olive [Elaeagnus umbellata Thunb.], Russian olive [Elaeagnus angustifolia L.], and thorny olive [Elaeagnus pungens Thunb.]) are invasive in North America. Elaeagnus pungens is prevalent throughout much of the southeastern United States, commonly overtaking wooded and natural areas, bottomlands, and roadsides. While many management methods, including several herbicide treatments, have been evaluated, the efficacy of these methods can vary based on the size and density of the target plants. Further, personal communication with land managers revealed a lack of information that incorporated application effort, duration, and associated cost into treatment efficacy and usefulness. We evaluated three herbicide application methods using the free acid formulation of triclopyr in an E. pungens–infested forest in South Carolina, USA, to determine the effectiveness of each application method. We estimated pretreatment E. pungens biomass and destructively harvested all live material posttreatment to obtain actual biomass values. Foliar herbicide application was ineffective, but both cut stump and basal bark application nearly eliminated E. pungens in the treatment plots. The basal bark application took slightly more time to complete than cut stump treatments but was described as less physically demanding by applicators. Based on treatment efficacy and time required, the basal bark application method seems most prudent for controlling E. pungens in these areas. These results will help land managers more effectively use their resources for invasive woody plant control.

Introductions of new crops can provide alternate market opportunities, but also may pose ecological risks. New crops lack established management, have uncertain performance issues, and may become weedy in their introduced region. The introduction of hemp (Cannabis sativa L.) into southern Florida poses a unique introduction scenario because of the subtropical climate and no commercial production on record, unlike in other eastern and midwestern U.S. states. We assessed the escape from cultivation for hemp by tracking establishment and reproduction of volunteer plants from the earliest modern hemp planting in Florida. Hemp is a weed across much of the United States matching its historical distribution and has been assessed to be of high invasion risk for Florida because of its biological attributes, history of escape, and colonization in other states and countries. We conducted monitoring of volunteer plants and a seed establishment experiment in southern Florida finding that hemp volunteer plants occurred in pulses over time, with variable and declining germination. Volunteer plants persisted for up to 2 yr and appeared in areas that were disked and mowed according to USDA-approved hemp crop termination procedures. In the seed establishment experiment, we found that hemp established in disturbed soils (∼9% of seeds planted) and that mean plant heights and seed counts were positively related to soil disturbance and nutrient addition. These findings showed that hemp plantings should be monitored for volunteer establishment, and containment plans should be in place to control the establishment of volunteer hemp plants in agricultural fields. Our study further illustrates the need for multiyear monitoring and repeat termination procedures to ensure containment of hemp volunteers. There was limited evidence of volunteer establishment in surrounding areas and on undisturbed land. However, seed containment, equipment cleaning, and the monitoring of nearby fields and seed transportation routes remains warranted.

Wingleaf primrose-willow (Ludwigia decurrens Walter) is a pervasive rice (Oryza sativa L.) weed native or naturalized to South America, the Caribbean, and the southeastern United States. While it was first noted in California in 2011 and provided with the highest pest rating “A” by the California Department of Food and Agriculture, enforcing eradication or quarantine was relatively disregarded, and it did not appear to spread significantly past its initial infestation area. Here, we report the spread within four counties (Butte, Placer, Shasta, and Tehama) of California, for which it has been found up to 184 km away from the initial infestation, and the expansion of the initial infestation within Butte County. As L. decurrens is already a problematic rice weed in parts of Asia, Africa, India, and the United States, monitoring new infestations is pivotal to prevent negative economic and environmental consequences to California and the United States.

Lindenleaf sage (Salvia tiliifolia Vahl) is an annual plant native to Mesoamerica that thrives in tropical, seasonally dry environments. It was introduced to Ethiopia in the late 20th century and made its way to the Tembien highlands in Tigray in 2018. With its many branching stems and profusion of seeds, this upright pioneer plant becomes dominant in the herbaceous layer of intensively used rangeland and roadsides before spreading to areas with other land uses, including agricultural land. Visual observations show that S. tiliifolia is not prevalent in areas with less grazing pressure. Farmers uproot S. tiliifolia from their crops, which is rather simple, because this species is easily recognized and its roots do not withstand much force. On rangeland, weeding is labor-intensive. As an alternative, we recommend converting rangelands into managed exclosures to maximize grass production, with initial S. tiliifolia removal. Natural vegetation regrowth in infested places would keep the most significant S. tiliifolia seed supply under control and reduce the species’ invasion of farmlands.

Stylosanthes viscosa (L.) Sw. (Fabaceae) is a herbaceous legume with a native range that includes much of the Neotropics, from Argentina to Texas and several West Indian islands. Except for native populations in Texas, there are no published records of this species growing outside cultivation in the continental United States. Here, I report extensive populations of S. viscosa in southeastern Florida, often growing in near monoculture, with an observed range spanning more than 35 km from Lakewood Park to Port St Lucie in St Lucie County and to Jensen Beach in northernmost Martin County. These populations may have descended from plants imported from Brazil and grown at the Agricultural Research Center (now the Indian River Research and Education Center) in Fort Pierce, St Lucie County, where at least one field of this species growing in near monoculture persists. Stylosanthes viscosa has the potential of becoming a dominant invasive species in and adjacent to open habitats in peninsular Florida.

Hydrilla [Hydrilla verticillata (L. f.) Royle], an invasive aquatic weed, has had a rich introduction history into the United States, with multiple subspecies being introduced since the 1960s. The most recent occurred before 2016, when northern hydrilla (Hydrilla verticillata ssp. lithuanica) was discovered in the Connecticut River. By 2021, following a 3-yr survey from Agawam, MA, to the Long Island Sound by the Connecticut Agricultural Experiment Station Office of Aquatic Invasive Species, H. verticillata ssp. lithuanica was found in more than 113 km of the river, occupying 344 ha. Since this survey, there has been concern that H. verticillata ssp. lithuanica would spread to nearby waterbodies and have a significant negative impact. Here, we report the first documented spread and establishment of H. verticillata ssp. lithuanica from the Connecticut River to five waterbodies in Connecticut and one in Massachusetts. Of the eight sites where H. verticillata observations were made, 75% (n = 6) were confirmed to be H. verticillata ssp. lithuanica and 25% (n = 2) to be Hydrilla verticillata ssp. peregrina (wandering hydrilla). Except for one site, all six locations infested with H. verticillata ssp. lithuanica provide watercraft access through public or private boat ramps. The authors also postulate on the mechanisms facilitating the spread and establishment of this subspecies.

Invasive annual grasses such as medusahead [Taeniatherum caput-medusae (L.) Nevski] and barb goatgrass (Aegilops triuncialis L.) are negatively impacting grasslands of the western United States. Over the last decade, research has shown that aminopyralid and other growth-regulator herbicides applied just before flowering greatly reduce viable seed production in several invasive annual grasses. Moreover, it has been shown with T. caput-medusae that using aminopyralid to reduce seed production in one year consistently reduces and sometimes nearly eliminates cover the following year. Our goal in this study was to extend this research to A. triuncialis, a weed for which limited herbicide and other management options exist. Based on previous research, we hypothesized aminopyralid applied several days before flowering at just 22% of the maximum registered rate (0.069 kg ae ha−1) would almost completely prevent production of viable A. triuncialis seeds in the greenhouse. In four experiments, aminopyralid reduced seed viability from between 65% and 95% to between 1% and 5%. Therefore, aminopyralid will likely control A. triuncialis in the field. Because aminopyralid is phytotoxic to many broadleaf species, it may be possible to use aminopyralid to simultaneously control mixed stands of invasive forbs, A. triuncialis, and T. caput-medusae. However, there are risks to applying aminopyralid where native and desirable nonnative forbs occur. Past research on T. caput-medusae suggests controlling A. triuncialis with aminopyralid will increase production of desirable annual forage grasses.

Predictive models of aboveground plant biomass derived from nondestructive measurements greatly assist in monitoring and surveying natural areas. Where invasive species are concerned, these models can provide insights to the impacts of invasions and efficacy of management strategies. Furthermore, tools that facilitate a rapid inventory allow for multiple assessments of impact over larger areas. Downy rose myrtle [Rhodomyrtus tomentosa (Aiton) Hassk.] is an invasive shrub in Florida and Hawaii that is native to southeastern Asia. Rhodomyrtus tomentosa was imported into Florida in the early 20th century through the ornamental plant trade and produces pink flowers and edible purple globe fruits. This woody shrub is particularly problematic in the understory of Florida’s mesic pine forests, where it forms dense, impenetrable thickets. To characterize the populations more accurately in Florida and build predictive equations for biomass that could be used to inform control methods, we established a network of sites from which we harvested individuals over 3 yr. Based on these measurements, we built a simple predictive equation for R. tomentosa dry biomass. Crown area strongly associates with biomass in a linear relationship (P < 0.001, R2 = 0.82). Fruit production is highly variable, but positively correlates to plant height in individuals that have reached reproductive size (plants below 1 m generally do not produce fruit), albeit weakly (P < 0.002, R2 = 0.27). We demonstrate here that two simple measurements—height and crown area—can accurately predict biomass and, to some degree, fruit production for R. tomentosa in Florida and may guide control methods by focusing on removing individuals larger than 1 m tall.

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.

Stem galls and witch’s broom–like growths are locally abundant on the highly invasive Brazilian peppertree (Schinus terebinthifolia) at field sites in southern Florida where a thrips biological control agent (Pseudophilothrips ichini) is being released to reduce the invasive potential of the plant. Galls have also been observed on potted plants in nursery stock grown to feed laboratory colonies of the agent. Herein, our objective was to isolate and identify the causal agent of the galls and assess its ability to induce galls in naive plants. We obtained stem galls from both field- and nursery-grown plants, aseptically isolated a fungus in acidic potato dextrose agar, and purified fungal colonies. Stems of potted naive saplings were wound-inoculated with purified hyphal fragments from the purified colonies, which readily induced galls like those observed in the field and nursery. Simultaneous molecular analysis of the fungal DNA obtained from the galls of field and nursery plants, experimentally induced galls, and fungal colony isolates identified this gall-inducing fungus as Cophinforma sp.. We demonstrated that this Cophinforma sp. can infect S. terebinthifolia stems via mechanical wounds and induce visibly discernible stem galls in saplings within 3 mo. This will serve as a model for galled plant production for assessing the impacts of the gall-inducing fungus on S. terebinthifolia, with potential for further study to investigate interactions between the thrips and this naturalized fungus, which may synergistically and/or additively enhance S. terebinthifolia management efficacy.

Tropical spiderwort (Commelina benghalensis L.) is a noxious invasive species and was detected in a long-term experiment in a research farm in Goldsboro, NC. A multistakeholder governance model was used to address the invasion of this species. Regulators insisted on the use of fumigation in all fields, but after intense negotiations, a multi-tier eradication plan was designed and implemented, allowing fumigation outside the long-term experiment and a combination of integrated approaches (including physical removal) and intense monitoring and mapping for long-term experimental fields. In the long-term experiment, C. benghalensis populations decreased logarithmically from more than 50,000 plants in approximately 80 ha in 2005 to 19 plants in less than 1 ha in 2019, with a projection of full eradication by 2024. Despite these results, which were considered to be proof of successful ecological management by university researchers, regulators decided to fumigate the fields containing the remaining 19 plants. This decision was made because regulators considered factors such as professional liability and control efficacy. This created serious disagreements between the different stakeholders who participated in the design of the original plan. Despite the goodwill all parties exhibited at the beginning of the governance process, there were important shortcomings that likely contributed to the disagreements at the end. For example, the plan did not include specific milestones, and there was no clarity about what acceptable progress was based on (i.e., plant numbers or the rate of population decline). Also, no financial limits were established, which made administrators concerned about the financial burden the eradication program had become over time. Multistakeholder governance can effectively address plant invasions, but proper definition of progress and the point at which the program must be modified are critical for success, and all this must be done within a governance model that balances power in the decision-making process.

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.

Fosamine ammonium (Krenite®) is a foliar herbicide that primarily targets woody plant species; however, formal evaluations of its efficacy and potential for non-target impacts are scarce in the literature. The few tests of fosamine ammonium that exist focus primarily on its use in open environments, and the value of fosamine ammonium in controlling invasive understory shrubs is unclear. Here, we test the impact of fosamine ammonium on invasive common buckthorn (Rhamnus cathartica L.) and co-occurring herbaceous plants across six forest sites in Minnesota, USA. Rhamnus cathartica treated with fosamine ammonium had a 95% mortality rate, indicating high efficacy of fosamine ammonium for use against R. cathartica. Non-target impacts varied between forbs and graminoids such that forb cover was reduced by up to 85%, depending on site, whereas graminoid cover was sparse and impacts of fosamine ammonium on graminoids were unclear. These results indicate that while fosamine ammonium can provide effective control of R. cathartica and other understory shrubs, there is potential for significant non-target impacts following its use. We therefore suggest that land managers carefully consider the timing, rate, and application method of fosamine ammonium to achieve desired target and non-target impacts.

Individual plant treatment (IPT) techniques (e.g., basal bark, cut stump, hack and squirt) are used for woody invasive plant management and often rely on small trigger-pump spray bottles as an economical and efficient way to deliver a herbicide to the target species. Worldwide, plastic suppliers produce many models and designs with a wide range of uses, including pesticide application. However, spray bottle performance has rarely been examined in relation to IPT techniques for operational invasive plant management. We tested 10 commonly available spray bottles for trigger output and variation over repeated strokes. We also examined sustained trigger sprayer performance over a 6-wk period for spray bottles containing water or basal oil carriers blended with amine and ester formulations of triclopyr, respectively. In the first study, we found significant differences in spray output per stroke between almost every bottle tested. Almost all spray bottle brands yielded outputs greater than 1.0 ml per stroke, which exceeds the maximum application amount specified for hack and squirt. Several bottles produced an output of greater than 2.5 ml per stroke. In the second study, the output per stroke was reduced for basal oil mixes, with significant reductions measured for two brands by 21 d and for all three brands tested by 42 d after mixing. These results indicate that consumer-grade trigger sprayers are likely to depreciate rapidly with routine operational use without proper hygiene maintenance. Even then it is likely that these application devices may need to be replaced several times annually. Trigger-pump spray bottles are an economical and practical solution for remote field operations and volunteer weed control activities. These sprayers are most suitable for spray-to-wet techniques such as basal bark and cut-surface treatments but may potentially be less suited for hack and squirt application, which often requires sub-milliliter precision.

Estimates of plant biomass are helpful for many applications in invasive plant science and management, but measuring biomass can be time-consuming, costly, or impractical if destructive sampling is inappropriate. The objective of this study was to assess feasibility of developing regression equations using a fast, nondestructive measure (cover) to estimate aboveground biomass for red brome (Bromus rubens L.), a widespread nonnative annual grass in the Mojave Desert, USA. At three study sites, including one measured for three consecutive years, B. rubens cover spanned 0.1% to 85% and aboveground biomass 1 to 321 g m−2. In log10-transformed linear regressions, B. rubens cover accounted for 68% to 96% of the variance in B. rubens biomass among sites, with all coefficients of determination significant at P < 0.05. For every doubling of percent cover, biomass was predicted to increase by 78%, 83%, and 144% among the three sites. At the site measured for three consecutive years, which ranged in rainfall from 65% to 159% of the long-term average, regression slopes each year differed from other years. Regression results among sites were insensitive to using cover classes (10 classes encompassing 0% to 100% cover) compared with simulated random distribution of integer cover within classes. Biomass of B. rubens was amenable to estimation in the field using cover, and such estimates may have applications for modeling invasive annual plant fuel loads and ecosystem carbon storage.

Tree-of-heaven [Ailanthus altissima (Mill.) Swingle] readily exploits disturbances, grows quickly into dense monocultures, and suppresses native plant species. The vascular wilt pathogen, Verticillium nonalfalfae, native to the eastern United States, has been proposed as a biocontrol agent for the invasive A. altissima. Studies consistently demonstrate the safety and efficacy of the bioherbicide, but they also note that the selective nature of the fungus does not preclude other invasive plants that commonly co-occur with A. altissima from occupying the site. We quantified the standing plant community and seedbank at several sites across Virginia 5 yr after inoculation with V. nonalfalfae to understand which species are present or being naturally recruited. Ailanthus altissima remained dominant in untreated areas but was nearly eradicated from the treatment plots. Other non-native species made up a large portion of the plant community and seedbank across all study areas, with no differences in their respective cover and count between treatments. While variability in plant community composition is high and site-specific context is important for establishing effective management strategies, planting native species and mitigating other invasives will be crucial to ensuring native species successfully establish in bioherbicide-treated areas.