Invasive plants need to be managed after wildfire to suppress the invasive plant and to maintain or restore a desired plant community. Our study tested treatments that influence species availability and performance following a disturbance (wildfire). The overall objective was to determine the ability of herbicide and revegetation treatments to restore spotted knapweed–infested areas to desired plant communities after wildfire. The study consisted of a factorial combination of three herbicide application treatments (broadcast application, spot application, and no herbicide) and three seed mixture treatments (grass-only seed mix, a grass and forb seed mix, no seeding). Picloram was used for the herbicide. Both the broadcast and spot picloram application methods decreased spotted knapweed cover and density up to 80% while increasing desired grass cover and density up to 20% compared with the control. However, broadcast spraying picloram decreased species richness from 5.7 to 3.6 species 0.1 m−2 and decreased desired forb density and cover compared with spot-applied picloram treatment. Spot spraying resulted in an increase in other undesired forbs compared with broadcast spraying. Seeding with desired species had no effect on spotted knapweed cover or density. Spot spraying may help maintain desired species richness while managing spotted knapweed.

Wild potato contains about 100 species that are native to the Americas from the southwestern United States to central Chile and adjacent Argentina, Uruguay, Paraguay, and southern Brazil. We report the occurrence of naturalized populations of the wild potato Solanum chacoense in seven sites in southern Australia, eastern China, England, New Zealand, the eastern United States, central Peru, and east-central Argentina. Modeling similar climatic niches on the basis of the distribution of S. chacoense from South America shows that observations of naturalized S. chacoense overlap with predicted areas. A literature review reveals that although S. chacoense possesses traits typical of an invasive species, all populations presently appear to be contained near their site of introduction.

Yellow starthistle is an invasive, annual, spiny forb that, for the past 30 yr has been steadily advancing up the Salmon River Canyon in west central Idaho. In 1994, a decision was made to attempt to manage yellow starthistle by establishing a complex of biological control agents in a containment zone where the weed was most dense. Between 1995 and 1997, six species of seedhead-attacking insects were introduced and successfully established. By 1999, the insects had spread through the entire containment zone. Following this dispersal, a rapid buildup of insect populations occurred, and, since 2003, seed destruction has fluctuated around 90%. Vegetation monitoring plots, however, have shown no consistent decline in the overall population of yellow starthistle, indicating that the amount of seed produced is still sufficient to allow full replacement. However, county weed control personnel, who are responsible for surveying and destroying outlying populations of yellow starthistle beyond the containment zone, report that, during this period, the number of new, isolated pockets of yellow starthistle they are finding has dropped dramatically. This case study discusses how the biological control program partially met the objective of managing yellow starthistle by reducing the rate of advance of this weed in the Salmon River Canyon.

The genus Asparagus includes at least six invasive species in Australia. Asparagus aethiopicus and A. africanus are invasive in subtropical Australia, and a third species, A. virgatus is naturalized and demonstrates localized spread in south east Queensland. To better understand how the attributes of these species contribute to their invasiveness, we compared fruit and seed traits, germination, seedling emergence, seed survival, and time-to-maturity. We further investigated dispersal ecology of A. africanus, examining the diet of a local frugivore, the figbird (Sphecotheres viridis) and the effect of gut passage on seedling emergence. Overall, A. aethiopicus was superior in germination and emergence, with the highest mean germination (98.8%) and emergence (94.5%) under optimal conditions and higher emergence (mean of 73.3%) across all treatments. In contrast, A. africanus had the lowest germination under optimal conditions (71.7%) and low mean seedling emergence (49.5%), but had fruits with the highest relative yield (ratio of dry pulp to fruit fresh weight) that were favored by a local frugivore. Figbirds consumed large numbers of A. africanus fruits (∼30% of all non-Ficus fruits), and seedling germination was not significantly affected by gut passage compared to unprocessed fruits. Asparagus virgatus germinated poorly under cool, light conditions (1.4%) despite a high optimum mean (95.0%) and had low mean performance across emergence treatments (36.3%). The species also had fruits with a low pulp return for frugivores. For all species, seed survival declined rapidly in the first 12 mo and fell to < 3.2% viability at 36 mo. On the basis of the traits considered, A. virgatus is unlikely to have the invasive potential of its congeners. Uniformly short seed survival times suggest that weed managers do not have to contend with a substantial persistent soil-stored seed bank, but frugivore-mediated dispersal beyond existing infestations will present a considerable management challenge.

This project summarizes the opinion of 52 experts on the future research needs in the area of invasive plants in California. Experts included academics at private and public universities, Cooperative Extension educators, land managers, members of nongovernmental organizations (NGOs), employees of restoration companies, and federal, state, and local agency personnel. Surveys were conducted through in-person interviews, written questionnaires, and workshops. The objective was to identify high-priority needs for future research on issues related to invasive plants in California's wildlands. More specifically, the goals were to (1) create a forum for assessing high-priority research needs, (2) guide future research toward these high-priority needs, and (3) facilitate connections and interactions among academic disciplines and between researchers and practitioners by increasing awareness of the range of ongoing research on invasive plants. Priority needs were chosen for 10 broad research topic areas, with specific subtopics addressed within each of these areas. In addition to noting specific research areas, there was a general need expressed for a synthesis of existing scientific information, particularly about the biology and ecology of invasive plants and the ecological impacts, control and management tools, restoration activities, and related social issues surrounding invasive plants. A mutual exchange of information was also considered important among the academic researcher and the field practitioner, as was the development of more effective training programs for land managers.

Understanding the relative importance of various functional groups in minimizing invasion by medusahead is central to increasing the resistance of native plant communities. The objective of this study was to determine the relative importance of key functional groups within an intact Wyoming big sagebrush–bluebunch wheatgrass community type on minimizing medusahead invasion. Treatments consisted of removal of seven functional groups at each of two sites, one with shrubs and one without shrubs. Removal treatments included (1) everything, (2) shrubs, (3) perennial grasses, (4) taprooted forbs, (5) rhizomatous forbs, (6) annual forbs, and (7) mosses. A control where nothing was removed was also established. Plots were arranged in a randomized complete block with 4 replications (blocks) at each site. Functional groups were removed beginning in the spring of 2004 and maintained monthly throughout each growing season through 2009. Medusahead was seeded at a rate of 2,000 seeds m−2 (186 seeds ft−2) in fall 2005. Removing perennial grasses nearly doubled medusahead density and biomass compared with any other removal treatment. The second highest density and biomass of medusahead occurred from removing rhizomatous forbs (phlox). We found perennial grasses played a relatively more significant role than other species in minimizing invasion by medusahead. We suggest that the most effective basis for establishing medusahead-resistant plant communities is to establish 2 or 3 highly productive grasses that are complementary in niche and that overlap that of the invading species.

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.

Dispersal is a critically important process in the spread of invasive plants. Although knowledge of dispersal will be crucial to preventing the spread of invasive plants, little research has been performed within this context. Many important invasive or agricultural weeds disperse their seeds via tumbling, yet only one previously published paper investigated this dispersal mechanism. Field and wind tunnel experiments were conducted to quantify and model tumbling dispersal. We developed competing models for diffuse knapweed seed dispersal from wind tunnel experiments and compared predictions to data collected from a field site in Colorado. Seeds were retained in plants that had traveled hundreds to as much as 1,039 m (3,408 ft). Although neither model accurately predicted dispersal when compared with independent field data, surprisingly, seed retention with distance was somewhat better described as a linear process than as exponential decay. Wind tunnel trials showed no evidence that the number of seeds deposited per meter depended on plant size. Thus, fecundity might be a key factor determining seed dispersal distances; plants with higher fecundity might disperse seeds over longer distances than those with fewer seeds.

The identification of privet in the middle southern United States can be difficult. Because most introduced species of privet can be invasive, and recent mapping projects seek location and species population data, proper identification is important. Without proper identification of privet species, data on species distributions and other pertinent information regarding invasiveness could lead to improper conclusions. Currently, information on privet identification is scattered throughout a number of reference materials. The purpose of this publication is to assist with the proper identification of escaped privet species, and suggest management options.

Caucasian Old World bluestem (OWB) has escaped into native rangelands and could have unknown effects on distribution, utilization, growth, and reproduction of native plant and animal species. This trial was established to determine the rate and timing of glyphosate application that will provide the greatest OWB suppression. Treatments included glyphosate applied early at the five-leaf stage of growth with 1.12, 2.24, or 3.36 kg glyphosate ai ha−1 (1, 2, or 3 lb ai ac−1), sequential application with an early glyphosate application of 1.12, 2.24, or 3.36 kg ha−1 followed by a second application 8 wk later of either 1.12 or 2.24 kg ha−1, and a late-only application of 1.12, 2.24, or 3.36 kg ha−1. Sequential glyphosate applications with at least one of the early or late applications being 2.24 kg ha−1 or more reduced OWB frequencies from over 87% to below 30% each year. During a moist year, all sequential application treatments reduced OWB frequency to 12% or less. Frequency of OWB the year after application was directly related (r2 = 0.91) to the total amount of glyphosate applied during dry conditions. Seed heads were absent or nearly absent in all sequential application treatments, with the exception of glyphosate at 1.12 kg ha−1 applied early and late during the dry season. Sequential application of glyphosate that includes one treatment either early or late of 2.24 or 3.36 kg ha−1 appears to be the most effective treatment to reduce established OWB during dry years. During years of adequate moisture, a single late application of 2.24 or 3.36 kg ha−1 or sequential applications with 1.12 kg ha−1 at each application is as adequate as sequential applications with greater rates for reducing OWB frequency and achieving OWB control.

Large-statured invasive grasses (LSIGs) constitute a distinct functional group with characteristic life history traits that facilitate colonization and aggressive growth in aquatic ecosystems, particularly those modified by human activities. These species typically form monocultures in the systems they invade and have wide-ranging and negative impacts on biodiversity and ecosystem processes. In March 2008, a special symposium was held as part of the Western Society of Weed Scientists annual meeting to synthesize our current knowledge of the ecological impacts and management of two notorious LSIGs: Arundo donax and Phragmites australis. In this volume of Invasive Plant Science and Management, symposium participants provide articles summarizing existing knowledge, recent research progress, and research needs for these two taxa. Here, we summarize the basic biology of these species and suggest the use of a more holistic approach to deal with the effects and management of LSIG invasions.

Navua sedge, a member of the Cyperaceae family, is an aggressive weed of pastures in Fiji, Sri Lanka, the Malay Peninsula, Vanuatu, Samoa, the Solomon Islands, and Tahiti and is now a weed of pastures and roadsides in north Queensland, Australia. Primarily restricted to areas with an annual rainfall exceeding 2,500 mm (98.4 in), Navua sedge is capable of forming dense stands, smothering many tropical pasture species. Seventeen herbicides were field tested at three sites in north Queensland, with glyphosate, halosulfuron, hexazinone, imazapic, imazapyr, or MSMA as the most effective for Navua sedge control. Environmental problems, such as persistence in soil, lack of selectivity, and movement off-site, may occur using some herbicides at the predicted 90% lethal concentration (LC90) control level rates. A seasonality trial using halosulfuron (97.5 g ai ha−1 [1.4 oz ac−1]) gave better Navua sedge control (84%) by spraying in March to September than by spraying at other times (50%). In a frequency trial, sequential glyphosate applications (2,160 g ae ha−1) every 2 mo was more effective for continued Navua sedge control (67%) than a single application of glyphosate (36%), although loss of ground cover would occur. In a management trial, single applications of glyphosate (2,160 to 3,570 g ae ha−1) using either a rope wick, ground foliar spraying, or a rotary rope wick gave 59 to 73% control, whereas other treatments (rotary hoe, 3%; slashing, −13%; crushing, −30%) were less effective. In a second management trial, four monthly rotary wick applications were much more effective (98%) than four monthly crushing applications (42%). An effective management plan must include the application of regular herbicide treatments to eliminate Navua sedge seed being added to the soil seed bank. Treatments that result in seed burial, for example, discing, are likely to prolong seed persistence and should be avoided. The sprouting activity of vegetative propagules and root fragmentation also needs to be considered when selecting control options.

Genetic diversity and reproductive characteristics may play an important role in the invasion process. Here, we review the genetic structure and reproductive characteristics of common reed and giant reed, two of the most aggressive, large-statured invasive grasses in North America. Common reed reproduces both sexually and asexually and has a complex population structure, characterized by three subspecies with overlapping distributions; of which, one is introduced, one native, and the third is of unknown origins. These three subspecies show varying levels of genetic diversity, with introduced common reed having high levels of nuclear diversity, indicating that multiple introductions have likely occurred. In contrast, giant reed has low genetic diversity and appears to reproduce solely via asexual fragments yet is highly aggressive in parts of its introduced range. Both species are well-adapted for growth in human-dominated landscapes, which is presumably facilitated by their rhizomatous growth habit.

Beach vitex is an invasive plant of coastal areas of the southeastern United States from Maryland to Georgia. Many resources have been dedicated to the control of established beach vitex stands. Successful eradication will require knowledge of this plant's ability to reestablish from seed after control efforts. To understand seed-based regenerative potential, studies were conducted to characterize the fruits and seeds, document the existence and size of seed banks, determine stratification requirements for germination, and ascertain seed dormancy mechanisms. Studies of fruit lots from three consecutive years (2003 to 2005) found that the average fruit contained 1.39 seeds, and more than 76% of fruits contained at least one viable seed. A positive correlation existed between seed number and both fruit mass and fruit diameter. A substantial soil seed bank was discovered that contained viable seeds 4 yr after vegetation removal. Stratification was required for seed germination. All stratification treatments induced germination, with highest rates realized when stratification was performed at 10 C for 8 or 12 wk. Germination rates were modestly increased (from 0 to 17%) through mild scarification in the absence of stratification. Results indicate that beach vitex has physical (fruit coat) and physiological (seed) dormancy mechanisms that are capable of delaying germination for multiple seasons, allowing development of a soil seed bank. Beach vitex can reestablish from seed after vegetation removal.

The rapid progression of an invasive genotype of common reed along roads and other linear infrastructures in North America provides one of the most spectacular examples of the role of transportation corridors as invasion pathways. In this paper, we discuss ecological patterns and processes in roadside habitats important for understanding the invasion dynamics of common reed from coastal areas inland. Frequent disturbances in roadsides combined with potentially high levels of nutrients from adjacent land and stress conditions (from deicing salt and other pollutants) mimic the conditions unfortunately found more and more in natural wetlands. The novel contribution of roads is the creation of linear wetlands with an unprecedented level of connectivity. Genetic evidence shows that invasion inland coincides with the intensification of the road network. Time series analysis of remote sensing data reveals impressive rates of invasion of roadsides and other linear infrastructures, suggesting prime conditions for common reed in these novel habitats. Whereas reed dispersal along roads was thought to be largely due to rhizome transport, new evidence suggests a significant contribution of sexual reproduction and seedling establishment, likely enhanced by climate warming at northern latitudes. There is little evidence that other wetland plants can slow down vegetative expansion of common reed in roadside habitats, but plant cover could prevent seedling establishment and shading by shrubs and trees limit lateral clonal expansion. The fact that common reed possibly provides water treatment and other ecosystem services in roadsides must be carefully weighed against the threat to biodiversity in natural systems. All this begs for investigating urgently if, where, and how we should intervene without compromising the great value of wetlands of conservation interest intersected by roads.

The common reed invasion in North America has spanned two centuries and is still ongoing. This expansion comprises two main forms: an introduced Eurasian lineage (identified here as “Introduced Phragmites”) and a Gulf Coast lineage of unknown origin (identified here as “Gulf Coast Phragmites”). Both lineages are spreading beyond their current ranges and are colonizing Southwestern and Gulf Coast ecosystems where they have not previously existed. As a result, the native North American lineage of common reed (hereafter “native Phragmites”) has declined in many places. The recent invasion of the U.S. Southwest by Introduced and Gulf Coast Phragmites lineages has made this the only region in the world colonized by all three lineages. Along the central Gulf Coast where Gulf Coast Phragmites remains the dominant form, Introduced Phragmites has also recently invaded the Mississippi River delta. The consequences of these new invasions are uncertain, but a rapid response is needed to protect native species and ecosystems and reduce future control costs.

Amur honeysuckle recovery following treatments annually and only in 1-year, during 2002 to 2009, was compared in the forests of Radnor Lake State Natural Area in Nashville, TN. Annual treatment areas had significantly lower mean Amur honeysuckle plant counts than 1-yr treatment areas for both ≤ 1 m (3.3 ft) and > 1 m plant heights and on both sloped and level areas, except for plants ≤ 1 m tall on level areas, which most likely indicated more soil moisture increasing seedling establishment and root sprouting in the first year after treatment. The significant, positive Pearson's product moment correlations for Amur honeysuckle counts of plants ≤ 1 m tall, with arboreal basal area and with canopy species diversity in the level areas of the annual treatment plots, were also most likely evidence for the importance of greater soil moisture during the first year after treatment for greater Amur honeysuckle recovery. For land managers interested in native vegetation restoration, guidance is provided to plan for long-term, invasive plant species treatment and recovery monitoring.

The effect of invasive species might be lessened if herbivores reduced transpiration and growth rates; however, simply removing photosynthetic material might not ensure that the transpiration rate of active leaf tissue decreases. We assessed whether biological control has an injurious effect on the target plant species, giant reed (Arundo donax), by quantifying leaf photosynthetic and transpiration responses to two herbivores: an armored scale, Rhizaspidiotus donacis, and a stem-galling wasp, Tetramesa romana. Herbivory by a sap-feeding scale and a stem-galling wasp both separately and together, reduces the rates of leaf level physiological processes in A. donax. The effect of the wasp increases with density and reduces photosynthesis by reducing the carboxylation rate of ribulose-1,5-bisphosphate carboxylase oxygenase, which controls CO2 fixation in photosynthesis. The scale insect reduces photosynthesis by decreasing the maximum rate of electron transport, which determines how much light energy can be captured in photosynthesis. The effect of the armored scale takes approximately 5 mo after infestation, which coincides with generation time. When both insects are present at the same time, the effect of their herbivory appears additive after time for the scale to reproduce. We conclude that a combination of two herbivores can have a stronger physiological effect than one type of herbivore, likely because of their different effects on leaf function.