Russian knapweed is an outcrossing perennial invasive weed in North America that can spread by both seed and horizontal rhizomic growth leading to new shoots. The predominant mode of spread at the local scale and dispersal at the long-distance scale informs control but has not been quantitatively researched. We used amplified fragment-length polymorphisms (AFLPs) of DNA collected from 174 shoots in two discrete patches of Russian knapweed at each of three locations in Montana. Out of the 174 shoots collected, we found nine AFLP genotypes. Three out of the six patches were monotypic; the other three patches each had one rare genotype. No genotypes were shared between patches. The maximum diameter of a genet (a genetic individual) was 56.5 m. These results indicate that patch expansion at the local scale is almost entirely by rhizomes that spread and develop new shoots. At the long-distance scale, dispersal is by seed. Controlling seed development through biological control and herbicide use may be effective at stopping long-distance dispersal but may not affect expansion of existing patches.

Many naturalized populations of the invasive tree princess tree exist in North America, yet little research has quantified its effect on native plant communities. A series of recent wildfires in the Linville Gorge Wilderness Area (LGWA) promoted multiple large-scale princess tree invasions in this ecologically important area. To measure community shifts caused by these princess tree invasions across burn areas, we sampled vegetation in paired invaded and noninvaded plots in mature and immature invasions within two burn areas of the LGWA. Plant community composition shifted in response to princess tree invasion across all invasion stages and burn areas. Species richness and Shannon diversity values decreased in invaded plots. Overall community structure also differed in invaded plots within immature invasions (P=0.004). The distribution of princess tree age classes in both burn areas indicates that fire promotes invasion but is not necessary for subsequent recruitment. Additionally, preliminary genetic analyses among distinct princess tree populations revealed very low genetic diversity, suggesting that a single introduction may have occurred in the LGWA. This information regarding community shift and strong post-fire recruitment by princess tree may inform management decisions by prioritizing princess tree control immediately after wildfires and immediately before and after prescribed burns.

Pale swallowwort and black swallowwort are European viny milkweeds that have become invasive in many habitats in the northeastern United States and southeastern Canada. A multiyear seedbank study was initiated in fall 2011 to assess annual emergence of seedlings and longevity of seeds of pale swallowwort and black swallowwort at four different burial depths (0, 1, 5, and 10 cm) over 4 yr. One hundred swallowwort seeds were sown in seed pans buried in individual pots, and emerged seedlings were counted and removed from May through September each year. A subset of seed pans was retrieved annually in October, and recovered seeds were counted and tested for viability. The majority of seedling emergence occurred during the first year (92% in 2012), and no new seedlings emerged in the third (2014) or fourth (2015) years. Pale swallowwort had relatively poor emergence at sowing depths of 0 cm (11%), 5 cm (6%), and 10 cm (0.05%—only one seedling), while 37% of pale swallowwort seeds emerged at 1 cm. The larger-seeded black swallowwort was more successful, with two-thirds of all sown seeds emerging at depths of 1 cm (71%) and 5 cm (66%), and 26% emerging at 10 cm. Only 16% of the surface-sown black swallowwort emerged. A large portion of the seeds that germinated at 10 cm, as well as at 5 cm for pale swallowwort, died before reaching the soil surface. Of filled seeds that were recovered in 2012 (black swallowwort at the 0-cm depth), 66% were viable. No viable seeds were recovered after the second growing season. Seeds recovered following the third year had become too deteriorated to accurately assess. Swallowwort seeds do not appear to survive more than 2 yr in the soil, at least in our experiment, suggesting that the elimination of seed production over 3 yr will exhaust the local seedbank. Seeds would need to be buried at least 10 cm for pale swallowwort but more than 10 cm for black swallowwort to prevent seedling emergence. Burial of swallowwort seeds as a management strategy may, however, only be practical in natural areas where high swallowwort densities occur.

Two of the five species of European blackberry (Rubus fruticosus L. aggregate) along the West Coast of the United States are considered invasive. They are also similar in appearance. Biological control of invasive blackberry by Phragmidium violaceum, causal agent of a rust disease, had been under consideration when rust-diseased blackberry was discovered in Oregon in 2005. An investigation was initiated to determine whether this disease would be an important factor affecting population density of these blackberries. Surveys were made over a 5-yr period at more than 30 field sites in the Willamette Valley and along the Pacific coast of Oregon. Diseased and nondiseased blackberry specimens were collected for artificial greenhouse inoculations and for identification. The two blackberry species, Rubus armeniacus and R. praecox, were identified as the most invasive. They were readily distinguished morphologically on the basis of inflorescence and flower characteristics and to a certain extent by differences in primocane leaf and leaflet shape. Artificial greenhouse inoculation studies revealed that R. praecox was susceptible to the rust disease and that R. armeniacus was not. These results were confirmed during a field survey. Results of this investigation revealed that the rust disease will not be effective for biological control of R. armeniacus and other approaches to management of this particular species will be required.

Nonnative invasive species are one of the biggest threats to biodiversity worldwide. In many cases the extent of the area invaded by an invasive species is so substantial that there are simply insufficient resources to control and manage the full extent of the invasion. Efficient use of resources and best management practices are critical for achieving invasive species management goals. Systematic regional planning is one way to quantitatively prioritize different management actions across the landscape, and is a tool that could be applied to large-scale invasive species management. Spatial prioritization has been used in several wetland restoration planning studies, in forest restoration, and in riparian and watershed restoration. Spatial prioritization has not been used as extensively in invasive species management, yet there are clear opportunities for spatial prioritization methods to inform invasive species management. Here we apply results from species distribution models to create a prioritization framework for control of the invasive wetland grass common reed, one of the most problematic invasive plants in North American wetlands.

In the city of Tromsø in northern Norway, invasive Tromsø palm (Norwegian: Tromsøpalme; English: Persian hogweed) is widespread. Although Tromsø palm has negative impacts on biodiversity and contains a phototoxic sap that burns human skin, it is also considered to be a local symbol of Tromsø city and is appreciated by many inhabitants. This study examined private landowners’ characteristics, perceptions, and landowners’ regulation of invasive Tromsø palm on their parcels on Tromsø Island in 2012 (vegetation season: May–September) to provide information concerning which landowner groups could be assisted by official regulation. Eleven key informants and 17 landowners were interviewed. Afterward, Tromsø palm on Tromsø Island was mapped using aerial photos and street-level photos from Google Maps®/Google Street View® and fieldwork verification. This distribution map was superimposed on a property map in a geographic information system to produce a map showing private parcels that contained Tromsø palm and associated neighboring parcels that did not contain Tromsø palm. Questionnaires were mailed to the 441 owners of the selected parcels, and 199 of the returned questionnaires were analyzed. Tromsø palm was more likely to be fully regulated/absent on a parcel that was inhabited (particularly if the owner lived on-site) and less likely to be fully regulated/absent if the parcel was jointly managed by several households. These findings indicate that authorities could focus their management efforts on supporting regulation efforts of those private landowners who own currently uninhabited or rented-out parcels and landowners of parcels jointly managed by several households. Furthermore, those landowners who found regulation measures against the plant on Tromsø Island important tended to have partly or fully regulated Tromsø palm on their plots. This might imply that information campaigns from authorities might encourage more landowners to regulate Tromsø palm.

Aphthona spp. flea beetles were released in two ecological sites of the Little Missouri National Grasslands in southwestern North Dakota in 1999 to control leafy spurge. The change in leafy spurge density and soil seedbank composition was monitored to evaluate the effectiveness of the biological weed control agent and the associated change in plant communities 5, 10, and 15 yr after release in loamy overflow (valleys) and loamy sites (ridges). In 2014, 15 yr after release, leafy spurge stem density had decreased 94% from 110 to 7 stems m−2 in the loamy overflow sites and 88% from 78 to 9 stems m−2 in the loamy sites. Leafy spurge represented only 2% and 6% of the loamy overflow and loamy seedbanks in 2004, respectively, compared with nearly 67% and 70%, respectively, in 1999. There was a slow shift to reintroduction of native species into the seedbank over the last 15 yr. The number of desirable species increased to 21 by 2014 (more than three times the number of species in 1999) in the loamy overflow sites, and doubled to 14 species in the loamy sites, while less desirable forb species doubled in both sites. Desirable grass species doubled in the loamy overflow sites by 2014 but remained unchanged in loamy sites. Aphthona spp. successfully controlled leafy spurge for more than 15 yr without any additional control methods or costs to land managers and resulted in the slow return of a subset of native species.

Fig buttercup is a perennial herb native to Europe, temperate Asia, and northern Africa. In eastern North America, fig buttercup competes with native spring ephemerals, complicating control techniques. If chemical control could be shifted earlier in the year, the potential to negatively impact spring ephemerals would be reduced. We tested glyphosate applications on fig buttercup in northern Virginia under three early phenological phases (preflowering, early flowering, and 50% flowering) to assess the effectiveness of early-season treatment. Treating when approximately half of the plants in the population were in flower resulted in a 95% decline in fig buttercup. Treating when the first flower in the population had emerged resulted in a 90% decline. No later phenological phases were treated. Control of fig buttercup led to an increase in cover of Japanese stiltgrass, an invasive grass.

Aminocyclopyrachlor (AMCP) will control many invasive broadleaf weeds, but the susceptibility of desirable forbs is not widely known. Native prairie response to AMCP was evaluated near Fargo, ND, and Felton, MN, in the Northern Great Plains. Both sites had high floristic quality prior to treatment, with 33 and 80 different species at Fargo and Felton, respectively. AMCP was applied at 140 g ha−1 in July 2014 to coincide with leafy spurge and Canada thistle treatment timing. AMCP altered the plant communities and reduced foliar cover of undesirable species, high seral forbs (undisturbed stable communities), and low seral forbs (early succession in disturbed communities) at both locations at 10 and 14 mo after treatment (MAT). AMCP reduced Canada thistle and leafy spurge in Fargo and eliminated hedge bindweed, prickly lettuce, and black medic in Felton. High seral forb foliar cover was reduced at 10 and 14 MAT from 20% to 2% and 3% in Fargo and from 19% to 1.6% and 2% in Felton, respectively. The high seral forb species birdfoot violet, white panicled aster, northern bedstraw, Canada goldenrod, purple meadowrue, and American vetch were reduced at both locations. Low seral forb cover also decreased at 10 MAT from 22% to 10% in Fargo and from 12% to 1% in Felton, respectively. By 14 MAT, low seral species in Fargo recovered to 16%, but recovery was much slower in Felton and slightly increased to 1.5%. After treatment high and low seral monocot species increased at both sites, likely due to reduced competition from susceptible species. AMCP reduced richness, evenness, and diversity at both locations at 10 and 14 MAT; therefore, floristic quality declined. A decline in diversity is generally undesirable but could have beneficial effects if invasive weeds and other undesirable species are reduced or eliminated.

Exotic weed propagules (seeds or fruits) often contaminate goods intended for import into Australia. Biosecurity officers must identify such propagules to manage risks, prevent incursions, and decide on potentially costly actions such as cleaning, treating, or destroying cargo. According to observations made by the Australian Department of Agriculture and Water Resources, more than 20% of the propagules found by biosecurity officers currently cannot be identified. By far the most important weed families contributing to seed load of imported goods are the grass family (Poaceae) and the daisy family (Asteraceae), accounting together for approximately 80% of cases. To facilitate fast and secure identification, increase the capabilities of biosecurity staff, and reduce the risk of weed incursions, we have developed an interactive digital identification key to the propagules of an initial priority list of 43 species of Asteraceae.