We investigated the single and combined effects of two biological control agents, the stem-mining weevil Hadroplontus litura and the pathogen Pseudomonas syringae pv. tagetis, with a herbicide (reduced or full application of glyphosate: 0.63 kg ae ha−1, or 3.78 kg ae ha−1, respectively) on the growth of Canada thistle, Cirsium arvense. We hypothesized that first, although each control method would have a negative effect on Canada thistle shoot biomass, root biomass, and shoot number, the integration of more than one control method would have greater impact than individual control methods. Second, we hypothesized that the order in which control methods are applied affects the outcome of the management program, with a pathogen application following weevil infestation being more effective than one prior to it. Although control methods impacted Canada thistle growth (P < 0.001, expect for a nonsignificant impact of glyphosate on shoot number), the combined effect of the three control methods behaved, generally, in an additive manner. A marginal interaction between the pathogen and the herbicide (P = 0.052) indicated a slight antagonistic interaction between these control methods. An interaction between the two biological control agents tested (P < 0.001) indicated that application of a pathogen prior to the release of weevil larvae could be more deleterious to Canada thistle than a late application. The observed, mostly additive, relationship between biological control agents and herbicides implies that integrating control methods rather than using a single approach could lead to greater Canada thistle control.

Black swallowwort [Vincetoxicum nigrum (L.) Moench] and pale swallowwort [Vincetoxicum rossicum (Kleopow) Barb.] are perennial vines of European origin that invade natural areas and perennial cropping systems in the northeastern United States and southeastern Canada. Both species reproduce via wind-dispersed seeds in the form of achenes with comas, but little is known about the extent of dispersal of these seeds. We studied the relationship of seed release height (0.75 m, 2 m), wind speed at the time of release, seed mass, and settling rate on distance traveled. Vincetoxicum nigrum and V. rossicum seeds traveled up to 72.1 and 79.6 m, respectively. Seeds of both species released from 2 m traveled greater distances than seeds released from 0.75 m, which fell within 20 m of the release point. Release height was the most important factor influencing long-distance dispersal events. Wind speed also strongly interacted with release height for long-distance dispersal of V. nigrum. Vincetoxicum nigrum seed mass was greater and settling rates faster than for V. rossicum. Increasing seed mass generally increased settling rate, which in turn decreased distance traveled, except in V. rossicum, for which longer distance–dispersing seeds had a faster settling rate. Our findings suggest that management efforts focus on reducing the presence of these two vines, especially if there is potential for them to climb up taller vegetation such as trees. Seeds released from these greater heights are more likely to travel far from source populations and initiate new populations. Preventing seed production in small, nonclimbing patches will also help suppress the expansion of these two vines, as seeds can still disperse up to 20 m away from parent plants.

Garlic mustard, a biennial forb native to Europe, has invaded native ecosystems in forested regions in the United States. In anticipation of a biological control program being implemented in the United States for this plant, a garlic mustard monitoring program was initiated. The objective of this study was to characterize garlic mustard populations and the associated plant communities and their response to environmental conditions in Minnesota hardwood forest ecosystems. Additionally, we developed a baseline for long-term studies to determine future benefits and impacts of biological control agents on plant communities infested with garlic mustard, should they be released. To monitor garlic mustard populations, we used a nationally standardized protocol in which data were collected on garlic mustard population density and cover, garlic mustard plant heights and silique production, insect damage to garlic mustard, cover of the associated plant community, and litter cover. We also collected data on available photosynthetically active radiation in the understory. The results underscore the variability in garlic mustard population dynamics. At only 6 of 12 sites did garlic mustard densities follow the predicted two-point cycles due to their biennial life cycle, with the first- or second-year life stage dominating in any given year. Available light did not differ strongly among sites, but shading by adult plants is implicated in keeping the populations of first-year plants low. Sites with greater garlic mustard cover had lower native species richness and cover than sites with lower garlic mustard cover. Absent biological control agents, garlic mustard is currently experiencing very little herbivory in Minnesota with an average of 2% of leaf area removed by herbivores. Our work shows the importance of pre-release monitoring at multiple sites over multiple years to adequately characterize populations. Without control, garlic mustard will likely continue to have negative impacts on northern forests.

Previous research showed growth regulator herbicides, such as picloram and aminopyralid, have a sterilizing effect on Japanese brome (Bromus japonicus Thunb.) that can reduce this invasive annual grass's seed production nearly 100%. This suggests growth regulators might be used to control invasive annual grasses by depleting their short-lived seed banks. The goal of this study was to extend the previous Japanese brome research to downy brome (Bromus tectorum L.), the most damaging invasive annual grass of U.S. grasslands. In a greenhouse, we found picloram did not greatly influence downy brome seed production, while point estimates suggest aminopyralid reduced seed production 55 to 80%. If not for a highly abnormal retillering response that we somewhat doubt would occur in the field, point estimates suggest aminopyralid would have reduced downy brome seed production approximately 90% when applied at the heading stage and approximately 98% when applied at three earlier growth stages. Our greenhouse study should encourage field studies designed to further explore the potential for using growth regulators to control downy brome and other invasive annual grasses.

Hybridization between two introduced plant species can influence the invasion capabilities of the exotic taxa, but the role of hybridization will likely differ in different invasions, even of the same species. Until now, studies concerning the ploidy of Japanese knotweed, giant knotweed, and their hybrids have been conducted in Europe or native ranges in Asia. Here, we assess the role of hybridization and ploidy in a U.S. invasion. We use flow cytometry to characterize DNA content in (1) established families in a common garden, (2) seedlings grown from common garden parents, and (3) wild populations. We also measured fertility in the garden and the field and vegetative growth traits in the garden. Although the majority of our parental and hybrid samples had ploidy levels previously documented in Europe (4X and 8X for parental species; 6X for hybrids), we found a wider range of knotweed cytotypes established in our garden (4X, 6X, 7X, 8X, 9X, and 10X) and additionally detected 5X, 11X, 12X, and possibly 14X ploidy levels in progeny from garden seed parents. The unexpected cytotypes were not confined to the greenhouse or common garden, in that all < 11X ploidy levels were also found in field populations in Massachusetts. In several cases, these data contradicted our expectations on the basis of morphological and molecular analysis, suggesting both significant introgression and the introduction of multiple cytotypes from Asia. With one exception (14X), we found all cytotypes were capable of strong vegetative growth, seed set, and the production of viable pollen. Without barriers to sexual reproduction, introgression is expected to progress, creating a progressively more diverse swarm of invasive genotypes.

Lesser celandine (Ranunculus ficaria) is an ephemeral perennial introduced to North America from Europe for ornamental use. This species is becoming widespread in shady, moist woodlands and lawns in the northern United States and southern Canada. Despite its invasive attributes, lesser celandine continues to be marketed by the nursery sector. A hardy and easy plant to grow, lesser celandine has a dense compact growth form that makes it ideal for border plantings and showy flowers that make it a desirable garden species for early spring color. The species easily escapes cultivation, colonizing primarily moist woodland habitats. Once established, lesser celandine creates a monoculture and is purported to displace native ephemeral species. Several factors make control of lesser celandine difficult, including a large root structure, which facilitates clonal reproduction and spread. The ephemerality of lesser celandine results in a relatively brief window in which to apply control measures. Land managers need to be aware of this common garden species as a potentially invasive weed and need to be able to differentiate it from the similar native marsh marigold. Effective management strategies are needed to protect native woodland understory species and biodiversity in natural and seminatural areas of affected regions.

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.

The continued threat of an invasive, annual brome (Bromus) species in the western United States has created the need for integrated approaches to postfire restoration. Additionally, the high germination rate, high seed production, and seed bank carryover of annual bromes points to the need to assay soil seed banks as part of monitoring programs. We sampled the soil seed bank to help assess the effectiveness of treatments utilizing the herbicide Plateau® (imazapic) and a perennial native seed mix to control annual Bromus species and enhance perennial native plant establishment following a wildfire in Zion National Park, Utah. This study is one of few that have monitored the effects of imazapic and native seeding on a soil seed bank community and the only one that we know of that has done so in a pinyon–juniper woodland. The study made use of untreated, replicated controls, which is not common for seed bank studies. One year posttreatment, Bromus was significantly reduced in plots sprayed with herbicide. By the second year posttreatment, the effects of imazapic were less evident and convergence with the controls was evident. Emergence of seeded species was low for the duration of the study. Dry conditions and possible interactions with imazapic probably contributed to the lack of emergence of seeded native species. The perennial grass sand dropseed outperformed the other species included in the seed mix. We also examined how the treatments affected the soil seed bank community as a whole. We found evidence that the herbicide was reducing several native annual forbs and one nonnative annual forb. However, overall effects on the community were not significant. The results of our study were similar to what others have found in that imazapic is effective in providing a short-term reduction in Bromus density, although it can impact emergence of nontarget species.

Native forbs are important for plant community function and diversity, and provide food and cover for wildlife. Field studies have been conducted throughout the western United States to determine the impact of herbicides applied to control invasive weeds on native forbs. However, locating adequate populations of native forbs for evaluation of tolerance to herbicides is often difficult. The susceptibility of nine native prairie forbs to aminopyralid applied at 30 to 120 g ha−1 was evaluated in a greenhouse study and results compared to the same or similar species in field trials. Forb susceptibility to aminopyralid varied by species. Of the forbs evaluated, azure aster, purple coneflower, and closed bottle gentian were the most tolerant to aminopyralid while prairie coneflower, great blue lobelia, harebell, and white prairie clover were the most susceptible and likely would be killed in the field. Blanket flower and showy goldenrod were moderately tolerant to aminopyralid even when applied at 120 g ha−1. The susceptibility of greenhouse-grown forbs to aminopyralid was comparable to results for the same or similar species in the field. Results from greenhouse trials could be used to predict native forb tolerance in the field.

Ecological restoration of shrub–steppe communities in the western United States is often hampered by invasion of exotic annual grasses during the process. An important question is how to create restored communities that can better resist reinvasion by these weeds. One hypothesis is that communities comprised of species that are functionally similar to the invader will best resist invasion, while an alternative hypothesis is that structurally more complex and diverse communities will result in more effective competitive exclusion. In this field experiment, we examined the effects of restored community structure on the invasion success of three annual grass weeds (downy brome, jointed goatgrass, and cereal rye). We created replicated community plots that varied in species composition, structural complexity and density, then seeded in annual grass weeds and measured their biomass and seed production the following year, and their cover after 1 and 3 yr. Annual grass weeds were not strongly suppressed by any of the restored communities, indicating that it was difficult for native species to completely capture available resources and exclude annual grass weeds in the first years after planting. Perennial grass monocultures, particularly of the early seral grass bottlebrush squirreltail, were the most highly invaded communities, while structurally complex and diverse mixtures of shrubs (big sagebrush, rubber rabbitbrush), perennial grasses (bluebunch wheatgrass and bottlebrush squirreltail) and forbs (Lewis flax, Utah sweetvetch, hairy golden aster, gooseberryleaf globemallow) were more resistant to invasion. These results suggest that restoration of sagebrush steppe communities resistant to annual grass invasion benefits from higher species diversity; significant reduction of weed propagule pressure prior to restoration may be required.

Nonnative Spartina species (cordgrasses) are widely distributed along the West Coast of North America, but have not invaded all bays with susceptible habitat. We used drift cards to assess the patterns and rates of potential Spartina propagule dispersal by ocean currents from estuaries with significant populations of one or more Spartina species. Cards were released monthly for 1 yr from Willapa Bay, Washington; Humboldt Bay, California; and San Francisco Bay, California; with recovery information reported by volunteers. Recovery rates averaged 37% for all release sites. Cards were commonly recovered close to their bay of release but were repeatedly found hundreds of kilometers both north and south of their release location. Cards most generally traveled northward from the release sites. Cards from Humboldt and Willapa bays were commonly recovered along the British Columbia coast, particularly in the winter. Cards released from Humboldt Bay were found farthest from their release sites. One card from Humboldt Bay traveled 2,800 km to Kodiak Island, Alaska. The timing of seed production, combined with prevailing currents, puts bays currently uninfested by Spartina at risk of repeated propagule loading by ocean currents. A coordinated coast-wide strategy for eradication of all nonnative Spartina will be critical to the success of individual bay-wide eradication efforts.

Nonnative, invasive plants are becoming increasingly widespread and abundant throughout the southwestern United States, leading to altered fire regimes and negative effects on native plant communities. Models of potential invasion are pertinent tools for informing regional management. However, most modeling studies have relied on occurrence data, which predict the potential for nonnative establishment only and can overestimate potential risk. We compiled locations of presence and high abundance for two problematic, invasive plants across the southwestern United States: red brome (Bromus rubens L.) and African mustard (Brassica tournefortii Gouan). Using an ensemble of five climate projections and two types of distribution model (MaxEnt and Bioclim), we modeled current and future climatic suitability for establishment of both species. We also used point locations of abundant infestations to model current and future climatic suitability for abundance (i.e., impact niche) of both species. Because interpretations of future ensemble models depend on the threshold used to delineate climatically suitable from unsuitable areas, we applied a low threshold (1 model of 10) and a high threshold (6 or more models of 10). Using the more-conservative high threshold, suitability for Bromus rubens presence expands by 12%, but high abundance contracts by 42%, whereas suitability for Brassica tournefortii presence and high abundance contract by 34% and 56%, respectively. Based on the low threshold (worst-case scenario), suitability for Bromus rubens presence and high abundance are projected to expand by 65% and 64%, respectively, whereas suitability for Brassica tournefortii presence and high abundance expand by 29% and 28%, respectively. The difference between results obtained from the high and low thresholds is indicative of the variability in climate models for this region but can serve as indicators of best- and worst-case scenarios.

To determine the extent and nature of container-grown plant soil as a pathway for introduction of exotic plant species to Alaska, soil from container-grown ornamentals was obtained from vendors and was incubated in the greenhouse. Fifty-four plant species were identified growing in containers or germinating from the soil, and included Canada thistle—a prohibited weed in Alaska—and nine other species listed as invasive in Alaska. The number of species and estimated seed bank were very low for soil from vegetable starts/herbs and herbaceous bedding plants (< 2 seedlings/L soil), but was greater for soil from containers containing woody plants, especially balled and burlapped ornamentals (20 seedlings/L soil). Container alien plant seed bank size was strongly related to type of soil. Potting (soil-less) soil contained 1.2 germinating seeds/L, soil-based soil 5.5 seeds/L, and mineral soil 18.7 seeds/L. Growers and vendors were variables that also influenced the size of the container seed bank, suggesting that weed management practiced during production and at the point of sale can greatly influence seed banks of ornamental containers.

Because of economic and environmental constraints, alternatives to chemical management of Canada thistle (Cirsium arvense) are frequently sought, but adequate nonchemical suppression of this invasive species remains elusive. Combining biological control with other tactics may be an effective approach to suppress Canada thistle, but more information is needed about how environmental conditions affect interspecific interactions. We investigated effects of a biocontrol agent (Hadroplontus litura, a stem-mining weevil) and a potential plant competitor (common sunflower, Helianthus annuus, native annual) on Canada thistle under two soil nutrient regimes in outdoor microcosms. Larval mining damage was relatively light, and weevils negatively impacted only main shoot height and flower number. All measures of Canada thistle performance were reduced when plants were grown with common sunflower or in reduced nutrients, although effects of the latter on root biomass were not significant. Effects of common sunflower and soil nutrients on Canada thistle were generally additive, though a marginally insignificant interaction indicated a trend for greatest flower number with high nutrients and absence of common sunflower. Effects of weevils and common sunflower on Canada thistle were also additive rather than interactive. Although larval damage ratings were significantly greater on plants grown in high-nutrient soil, under our experimental conditions weevils and soil nutrients did not have a significant interactive effect on Canada thistle plants. Our results indicate that H. litura is a relatively weak biological control agent, but when combined with competitive desirable vegetation, some level of Canada thistle suppression may be possible, especially if soil nutrient levels are not highly enriched from agricultural runoff. Assessing the true ecological impacts of Canada thistle infestations may be an important direction for future research.

The Sheyenne National Grassland (SNG) is a native tall grass and mixed grass prairie located in southeastern North Dakota. Approximately half of the SNG has been invaded by leafy spurge (Euphorbia esula L.) and control methods have been limited. Many herbicides cannot be utilized at the SNG due to sandy soils (> 80%) and shallow groundwater, nor can they be applied near the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles), a federally listed threatened plant found on the SNG. Quinclorac and aminocyclopyrachlor were considered for use on the SNG but potential to enter the groundwater was unclear. Movement of quinclorac and aminocyclopyrachlor was evaluated in 70 cm soil columns that simulated field conditions from five ecological sites. Quinclorac leached further following the heavy rainfall event of 15 cm in 48 h compared to the annual precipitation of 51 cm applied over 9 wk. Quinclorac leached approximately 45 cm into the soil profile averaged over all soil types and both precipitation events but never exceeded 65 cm regardless of soil type. Aminocyclopyrachlor leaching was greater than quinclorac and moved through all soil types into the leachate following both watering regimes. Desorption of both herbicides was incomplete. Approximately 10 and 32% of applied aminocyclopyrachlor and quinclorac, respectively, remained in the top 5 cm of soil regardless of soil type or watering regime. Quinclorac but not aminocyclopyrachlor was considered suitable for use at the SNG to control leafy spurge and has the added benefit of not harming the western prairie fringed orchid.

An open-field test was conducted in southern France to assess the host-specificity of Ceratapion basicorne (Illiger), a candidate for biological control of yellow starthistle. Test plants were infested by naturally occurring populations of C. basicorne but were also exposed to sympatric herbivore species, including other Ceratapion spp. Insects from the test plants were collected directly into tubes of ethanol and were subsequently identified to species according to DNA sequence similarity with morphologically identified reference specimens. This integrated, morphological and molecular identification method was used in an effort to maximize the amount of data gained in the field bioassay and to minimize the number of taxonomist–hours necessary to complete the study. The results obtained showed that the French C. basicorne population only attacked yellow starthistle and cornflower, another known host of C. basicorne. Molecular phylogenetic analysis of the insects collected from all other nonhost plants rejected the possibility that any were C. basicorne.

The objective of this article is to extend the reported period in which flood-distributed knotweed propagules may be successfully managed using only manual labor. During a second round of early detection and rapid response (EDRR) management along the Green River in Guilford, VT, we collected and measured all Japanese knotweed propagules that had been distributed by flooding approximately 21 mo earlier, in August 2011, at a single site. Our data suggest that knotweed s.l. prioritizes the growth of new stems over new rhizomes at the start of a growing season. Because the limiting factor for successful removal of new knotweed s.l. plants by hand is the size of the rhizome system, our findings support extending the time frame for EDRR management of flood-distributed knotweed s.l. into the second spring after its initial dispersal. Additionally, in November 2013, surveys of our work sites found no new knotweed s.l. plants in locations accessible to work crews. In addition to validating our EDRR management techniques, this implies that knotweed s.l. fragment viability does not extend past the second spring following its dispersal.

Data on 111 environmental weed eradication programs carried out by the New Zealand Department of Conservation (DOC) have been collected and summarized. A total of 21 programs were discontinued, and 90 are ongoing. Within the ongoing programs, four have been successful in that no plants remain at any known infestations. All four of the successful eradications had a total area across all infestations of less than 1 ha (2.5 ac); however, many similar-sized programs were not successful. Correctly assessing the extent of infestations appears to be a major problem for discontinued programs. Some of the ongoing programs are progressing toward eradication, but this is taking much longer than initially anticipated. The strongest determinant of progress toward eradication was found to be the identity of the DOC administrative area, for reasons that are only speculative. The number and area of initial infestations had no effect on progress toward eradication. However, the rate at which new infestations were located was negatively correlated with progress. Across many programs, progress was restricted by inconsistent infestation visitation. After running for a decade, DOC's weed eradication strategy has yet to provide significant dividends. Environmental weed eradication is clearly more difficult than has previously been acknowledged in New Zealand.

Rangeland health assessment provides qualitative information on ecosystem attributes. Successional management is a conceptual framework that allows managers to link information gathered in rangeland health assessment to ecological processes that need to be repaired to allow vegetation to change in a favorable direction. The objective of this paper is to detail how these two endeavors can be integrated to form a holistic vegetation management framework. The Rangeland Health Assessment procedures described by Pyke et al. (2002) and Pellant et al. (2005) currently are being adopted by land managers across the western United States. Seventeen standard indicators were selected to represent various ecological aspects of ecosystem health. Each of the indicators is rated from extreme to no (slight) departure from the Ecological Site Description and/or the Reference Area(s). Successional management identifies three general drivers of plant community change: site availability, species availability, and species performance, as well as specific ecological processes influencing these drivers. In this paper, we propose and provide examples of a method to link the information collected in rangeland health assessment to the successional management framework. Thus, this method not only allows managers to quantify a point-in-time indication of rangeland health but also allows managers to use this information to decide how various management options might influence vegetation trajectories. We argue that integrating the Rangeland Health Assessment with Successional Management enhances the usefulness of both systems and provides synergistic value to the decision-making process.

Jubatagrass is one of the most invasive plants along the California and southern Oregon coast. It establishes dense populations that can severely impact native plant diversity and conifer seedling recruitment following forestry operations. This goal of this study was to evaluate the effectiveness of both manual removal and several herbicide control options and application techniques. In addition, a cost analysis was also conducted for the most successful herbicide control methods. Results demonstrate that mechanical removal through digging is effective, although labor intensive. Among the herbicides tested, glyphosate applied as a high-volume (spray-to-wet) application (0.6% ae) in early summer, low-volume application (2.4% ae) in early summer or fall, and ropewick technique in early summer or fall (> 9.9% ae) all provided ≥ 88% jubatagrass control, but the low-volume treatments were the most cost effective. Although the graminicide sethoxydim at the highest rate (0.36% ai) did not give effective control, fluazifop applied in the fall in a low-volume treatment (0.98% ai) gave 87% control of jubatagrass. Imazapyr gave some level of control but does not appear to provide an economical option for jubatagrass management. Results of this study demonstrate that in addition to the more conventional methods of mechanical removal and spray-to-wet glyphosate (0.6% ae), control of jubatagrass can also be equally or more effective with low-volume and ropewick applications of glyphosate.