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.

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.

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.

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.

Russian thistle, also known as tumbleweed (Salsola spp.), is a problematic invasive plant found on natural and working landscapes. On a California rangeland, we tested the singular and interactive treatments of grazing, herbicide, and seeding to determine how these approaches might influence Salsola cover across a 5-yr experiment. Total Salsola cover declined by 3% annually during the study. A single spring treatment of chlorsulfuron + 2,4-D followed by glyphosate applied in the fall just before seeding, and then 2,4-D the following spring, significantly reduced Salsola cover compared with the untreated control. Seeded forage species cover increased over time and was significantly higher than seeded native species cover at 5 yr after seeding. However, the seeding treatment had no effect on Salsola cover. Although grazing did not reduce Salsola cover, due to the beneficial effects of grazing on reducing other nonnative species, this study supports the use of an integrated approach of herbicide application, grazing, and seeding to achieve management goals on an arid working landscape.

There are limited educational opportunities regarding aquatic invasive species (AIS) management that target laypersons. This is a significant gap, particularly as nonprofessionals are often tasked with making decisions about whether and how to pursue AIS control efforts, for example, through their roles in community lake associations. Thus, there is a need for educational programs to help consumers of AIS management services, “do-it-yourself” lakeshore homeowners, and other engaged nonprofessionals gain a stronger foundation in the science and practice of AIS management. We helped fill this unmet need through development of a new online course, AIS Management 101, that targets lakeshore property owners, lake association members, and other nonprofessionals engaged in AIS decision making, seeking to make them better-informed consumers. The course covers concepts ranging from basic invasive species biology to pesticide science, treatment evaluation, regulations and permitting, and nonchemical management tools. Participants in the course demonstrated significant knowledge gains through check-in and check-out knowledge assessments. Course participants also reported greater understanding of key issues pertaining to AIS management and application of this improved knowledge to actual management decisions following completion of the course. While this program focuses on management of aquatic invasive species, similar approaches could be applied to lay audiences engaged in management of terrestrial invasive species or other natural resource issues.

Sulphur cinquefoil (Potentilla recta L.) is an invasive perennial forb threatening rangelands in western North America. To identify best management strategies to control P. recta, we examined targeted goat (Capra hircus L.) grazing conducted once (pre-flowering) versus twice (pre-flowering and flowering and seed set), aminopyralid application, and integrated targeted grazing and aminopyralid as management strategies. We also examined the interaction between treatments and seasonality (spring and summer) and explored the possibility of off-target effects to non-target species. Two intermountain rangelands in British Columbia, Canada, were treated, one with targeted grazing treatments only and one with targeted grazing and herbicide treatments. Targeted grazing treatments were implemented in 2019 and 2020, and aminopyralid was applied once in 2019 at a rate of 56 g ai ha−1. Potentilla recta aboveground biomass and number of seed heads declined following targeted grazing treatments at both field sites in 2019 and 2020 when compared with the control, with no differences between targeted grazing treatments. In May 2020, before the implementation of targeted grazing for the second year, a decrease in P. recta biomass was not measured in the targeted grazing treatments, but biomass was 87% to 99% less in the herbicide-only and targeted grazing plus herbicide treatments. In July 2020, declines in biomass and seed heads in the herbicide-only and targeted grazing plus herbicide treatments did not differ from grazing twice, and aminopyralid effects did not differ among the three herbicide treatments. Further research is required to examine legacy effects of targeted goat grazing and aminopyralid on P. recta, establish reapplication frequency of treatments, and determine whether integrating targeted goat grazing and aminopyralid is needed in the long term to manage P. recta. A long-term study is also needed to examine off-target effects from targeted goat grazing and aminopyralid and ways to mitigate these effects to promote healthy native rangeland plant communities.

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.