Introduced plants threaten biodiversity and ecosystem processes, including carbon (C) and nitrogen (N) cycles, but little is known about the threshold at which such effects occur. We examined the impact of the invasive shrub Amur honeysuckle on soil organic carbon (SOC) and N density at study sites that varied in invasion history. In plots with and without honeysuckle, we measured honeysuckle abundance and size (basal area) and extracted soil cores. SOC and N densities were highest at the site with the longest invasion history and highest invasion intensity (i.e., greatest abundance and basal area of honeysuckle). Basal area of honeysuckle positively affected SOC and N densities likely because of increased litter decomposition and altered microbial communities. Because honeysuckle increases forest net primary productivity (NPP) and SOC, it also may play a role in C sequestration. Our results demonstrate the need to consider the influence of invasion history and intensity when evaluating the potential impact of invasive species.

Tall buttercup is an invasive forb that has been reported in all but eight states and one Canadian province. The species has been of concern in Montana where it has invaded over 8,300 ha, and it has been particularly problematic in irrigated hayfield meadows that are used for forage production. This study sought to develop an integrated management strategy to control tall buttercup while maintaining forage production. Research was conducted over 2 yr at flood-irrigated and subirrigated hayfield meadows near Twin Bridges, MT. Treatments were randomly applied in a split-plot design with four replications at both sites. Herbicide treatments occurred at the whole-plot level: nonsprayed, aminopyralid (172 g ai ha−1), aminocyclopyrachlor + chlorsulfuron (83 g ai ha−1 + 33 g ai ha−1), and dicamba (981 g ai ha−1). Split plots consisted of mowing and fertilization (28 kg N ha−1). All herbicides provided up to 2 yr of tall buttercup control at both sites. In the second year, aminocyclopyrachlor + chlorsulfuron and aminopyralid reduced tall buttercup by 93% and 96%, respectively, for the subirrigated and flood-irrigated sites. At the subirrigated site, mowing reduced tall buttercup by 71%, and fertilization reduced it by 57%. Forage decreased following aminocyclopyrachlor + chlorsulfuron treatments. The integration of herbicide, mowing, and fertilization did not improve tall buttercup control.

Napiergrass has potential as a cellulosic biofuel crop because of its rapid growth habit in the southern United States. However, it is also listed as a potential invasive species by the Florida Exotic Pest Plant Council. For field renovation, information about napiergrass control in response to tillage and herbicides is required. Field studies were initiated to evaluate control of napiergrass established in fields for over 3 yr at Plains, GA, and Tifton, GA. For tillage and POST herbicides, imazapyr plus glyphosate consistently controlled napiergrass relative to diclosulam plus glyphosate, sulfentrazone plus glyphosate, or tillage in terms of visual injury, stem height and dry biomass reduction. One application of imazapyr plus glyphosate controlled napiergrass 74 and 94%, and reduced plant stem height to 6 and 15% of the nontreated control. When diclosulam plus glyphosate, sulfentrazone plus glyphosate, or tillage was used alone with no sequential herbicides, napiergrass control ranged from 12 to 33%; when these control tactics were followed by two sequential applications of either sethoxydim or glyphosate, napiergrass control varied from 45 to 99%. Reductions in plant heights were reflective of injury 47 d after final herbicide applications (May/June). Napiergrass yield in dry biomass production was reduced by imazapyr plus glyphosate ≥ 86% relative to the nontreated control (NTC). Diclosulam plus glyphosate, sulfentrazone plus glyphosate, or tillage alone was not effective in reducing napiergrass dry biomass yields ranging from 1 to 47% compared with the NTC; when these treatments were followed by sequential applications of sethoxydim or glyphosate, napiergrass dry biomass was reduced 46 to 91% compared with the NTC. Tillage plus two applications of sethoxydim or glyphosate exhibited control potential because they provided levels of napiergrass control similar to imazapyr-based treatments. Tillage plus multiple applications of sethoxydim or glyphosate offers flexibility to crop rotations as compared with the residual herbicide imazapyr, which has many crop rotation restrictions because of carryover concerns.

Techniques for preventing crazyweed toxicity in livestock have generally fallen into two categories: excluding livestock access to infested ranges during early spring and fall, and controlling crazyweed populations through herbicide application. Although picloram has been used to control crazyweed effectively in the past, aminopyralid has shown efficacy at lower application rates, exhibits less potential off-target movement, and has been classified as a reduced-risk product. Differences in the response of silky crazyweed and nontarget grasses and forbs to picloram + 2,4-D and aminopyralid + 2,4-D were investigated. Picloram + 2,4-D was applied at a rate of 0.3 kg ae ha−1 picloram + 1.1 kg ae ha−1 2,4-D, and aminopyralid + 2,4-D was applied at a rate of 0.1 kg ae ha−1 aminopyralid + 1.2 kg ae ha−1 2,4-D. Silky crazyweed canopy cover, number of flowering stalks, plant size, and biomass decreased 15 mo after herbicide treatments (MAT) with average percentage of relative reductions of 92, 95, 90, and 99%, respectively. Crazyweed density decreased by 1.5 ± 0.2 SE plants m−2 and 1.3 ± 0.2 plants m−2, a relative reduction of 95 and 80%, 15 MAT in aminopyralid + 2,4-D– and picloram + 2,4-D–treated plots, respectively. Plots treated with aminopyralid + 2,4-D had 4% lower nontarget forb canopy cover than did picloram + 2,4-D plots 15 MAT. Grass biomass remained similar within treatments over time for control, aminopyralid + 2,4-D and picloram +2,4-D plots, and was similar in all plots 15 MAT. Plots treated with herbicides had, on average, 11% greater grass cover than did control plots 15 MAT (aminopyralid + 2,4-D: 89%; picloram + 2,4-D: 85%; control: 76%).

This paper describes postrelease monitoring of a population of Jaapiella ivannikovi, a gall-forming midge that was introduced for biological control of Russian knapweed. In 2011 to 2013, from late May to early June through August, we monitored 100 permanent plots at one of the first release sites of J. ivannikovi in central Wyoming. Based on the phenology of gall formation, an appropriate window for collection of galls to distribute to new sites is from early to mid-June through early August. Although J. ivannikovi established successfully, 4 yr after release, the percentage of ramets that were galled remained low (1 to 2%), indicating that J. ivannikovi is not yet having a significant effect on Russian knapweed at the site.

Wild parsnip is an invasive species with a global distribution in temperate climates. Parsnips are native to Eurasia and have been cultivated for more than five centuries. It is unclear whether the global invasion of this species is a consequence of escape from cultivation or the accidental introduction of a Eurasian wild subspecies. In this study, we used nuclear ribosomal DNA internal transcribed spacer (ITS) and chloroplast DNA (cpDNA) markers to evaluate the genetic structure of wild parsnip in its native range (Europe) and in three distinct geographic regions where it is considered invasive: eastern North America, western North America, and New Zealand. We also compared wild and cultivated parsnips to determine whether they are genetically distinct. From 112 individuals, we recovered 14 ITS and 27 cpDNA haplotypes. One ITS haplotype was widespread; few haplotypes were rare singletons. In contrast, at least two lineages of cpDNA haplotypes were recovered, with several novel haplotypes restricted to Europe. Cultivated parsnips were not genetically distinct from wild parsnips, and numerous wild parsnip populations shared haplotypes with cultivars. High genetic diversity was recovered in all three regions, suggesting multiple introductions.

Many conservation land managers working with invasive plants rely largely on their own experience and advice from fellow managers for controlling weeds, and rarely take into consideration the scientific literature, a concrete example of a knowing–doing gap. We argue that invasion scientists should directly teach managers best practices for control. In 2013, we created a training program on five invasive plant species, specifically tailored to Québec (Canada) environmental managers. The course material was science-based, and included details on methods and costs. Here, we explain how this idea emerged, how the program was constructed and which types of managers were targeted. With modest resources, we reached 163 managers in less than 18 mo, who collectively oversee invasive species management for 41% of the Québec population. We presented factual information for all control methods, giving the environmental managers the tools to critically and objectively assess various options. Participants especially appreciated the highly practical content of the training and that they could submit their own invasion case for discussion. This program represents significant progress in narrowing the knowing–doing gap associated with the control of invasive plants in Québec, and we encourage such initiatives elsewhere for all fields of invasion biology.

Biological invasions and climate change pose two of the most important challenges facing global biodiversity. Of particular importance are aquatic invasive plants, which have caused extensive economic and environmental impacts by drastically altering native biodiversity and ecosystem services of freshwater wetlands. Here, we used the maximum entropy model, Maxent, to model the potential range expansion of three nonnative aquatic invasive plants: alligatorweed, limnophila, and giant salvinia, throughout the continental United States under current, 2030 to 2059 (2040), and 2070 to 2099 (2080) climate scenarios. Maxent is a popular method to model predicted current and future species distributions based on biogeography and climate. Alligatorweed, limnophila, and giant salvinia are noxious invaders of freshwater habitats in the southeastern United States and cause economic and ecological loss. In addition, we analyzed each species' habitat preference based on wetland type, occurrence in man-made habitats, and distance to the nearest stream to better understand what future habitats are at risk and how these species spread. Our results show that in 2040 and 2080 climate scenarios, all three species have the potential to increase their range throughout the northeastern United States and as far as New York and Massachusetts. The spatial distribution of alligatorweed was primarily determined by precipitation of the warmest quarter (15.8%), limnophila was primarily determined by precipitation of the warmest quarter (52.2%) and mean temperature of the coldest quarter (21.8%), and giant salvinia was primarily determined by the mean temperature of the coldest quarter (24.3%). All three species were found significantly more frequently in lakes and ponds than in other freshwater habits. Giant salvinia was found significantly more often in man-made wetland habitats. In order to reduce the detrimental impacts of these species, land managers in the northeastern United States should concentrate early detection and rapid response management in lakes, ponds and man-made wetland habitats.