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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.
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.
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.
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.
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.
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.