Ventenata [Ventenata dubia (Leers) Coss.] is a nonindigenous, invasive grass in the inland Pacific Northwest (PNW) of the United States. It appears to be present in the PNW without any evidence of disease expression. Surveys of V. dubia in the PNW (Idaho, Montana, Oregon, and Washington) were entirely negative for fungi, including types of pathogens that might be expected in grasses (e.g., rust, powdery mildew, choke). In Europe, where V. dubia is native, fungi were documented (i.e., Septoria ventenatae Sandu, Tilletia fusca Ellis & Everh., and Tilletia elisabethae T. Denchev & Denchev) on V. dubia. In its native range there likely are natural enemies that may limit V. dubia abundance, and these may include fungal pathogens. Pathogens of V. dubia from its native range may hold potential for use as classical biological control agents in North America, and if deemed safe, could be introduced. To ascertain V. dubia’s native range, we compiled data from herbarium specimens, consulted with herbarium curators in the region, and searched relevant literature. We found that V. dubia primarily is reported in southern Europe and western Asia. Ventenata dubia has been reported only occasionally from North Africa in Algeria and Morocco. The common name “North Africa grass” likely originated from references to V. dubia in the 19th-century botanical explorations in Algeria of the French botanist, Ernest Cosson, who published the current scientific name based on a preexisting name in 1854. Another finding of interest is that the latitudinal range of collections from Europe and North Africa of V. dubia spans Tunisia to Finland. The plant may thus be adapted to a range of environments, indicating it could become more widely distributed in North America. Efforts to search its native range for pathogens should also consider the range of environmental conditions found within its native and introduced ranges.

Giant reed (Arundo donax L.) has recently shown great potential as a feedstock for the bioenergy industry. However, before A. donax can be grown commercially, due to its invasive nature, management strategies must be developed to reduce the risk of unintended spread. This research was conducted in northeastern Oregon (USA) during two growing seasons. Nine control strategies were evaluated in a field that previously had A. donax as a crop. The control strategies included mechanical practices (stem cutting and rhizome digging), physical practices (covering with an opaque tarp), chemical practices (glyphosate applications at different rates and timings), and a combination of these practices. Spring samplings of A. donax regrowth in the season following treatments indicated that stem cutting in the spring without follow-up control practices provided no control. Covering plants with a tarp after cutting them (either with or without a glyphosate treatment after cutting) resulted in 96% control. Application of glyphosate alone also resulted in excellent control, although timing of application was an important factor for maximizing efficacy. The best results were found when the maximum dose (10.2 L ai ha−1) was split among two or three applications (>99% of control) compared with the maximum dose applied once (75% to 94%). Control was lower (73% to 89%) for two of the strategies that included mechanical practices, stem cutting + glyphosate and rhizome digging, in comparison to other strategies involving tarps and/or glyphosate applications (88% to 100%). Results indicated that it is very difficult to eradicate volunteer A. donax in 1 yr, but very good control can be achieved with several of the strategies tested.

Russian-thistle (Salsola tragus L.), is a nonnative, C4 photosynthesizing, annual plant that infests disturbed and natural areas in the arid U.S. Southwest. Land managers of natural areas may need to decide whether a S. tragus infestation is potentially harmful and whether it should be actively managed. One factor informing that decision is an understanding of the conditions under which this weed emerges and establishes and how those processes affect where and when infestations occur. We studied S. tragus establishment on aeolian (windblown) sandy soils at Petrified Forest National Park, AZ. Our sites were a previously disturbed sand sheet and a semistabilized sand dune. Measurements in plots on these sites over two growing seasons revealed a similar number of S. tragus seedlings emerging on both sites early in the 2015 growing season. As the season progressed, S. tragus cover (seedling survival and growth) was lower on the sand dune, except for a plot placed entirely on a coppice mound. In 2016, S. tragus seedling emergence and development of cover, measured on plots at both sites, was exceptionally low, as was summer rainfall. A growth chamber assay of seedling emergence from soil and litter samples collected at each site showed emergence was greatest from samples collected where S. tragus litter remained on the soil surface, and otherwise was infrequent. Our study suggests that S. tragus emergence and early establishment are sensitive to low precipitation and that soil-surface microtopography and grass and shrub cover may be determinants of the spatial pattern of infestation on sandy soils. As aeolian sands occur throughout drylands of the U.S. Southwest, deeper understanding of the conditions under which S. tragus seedlings emerge and establish can inform management of this invasive annual in those habitats.

Babysbreath or perennial babysbreath (Gypsophila paniculata L.) is an aggressive invasive plant in large parts of southern Canada and the northern and western United States. It reproduces and disperses by seed, so the phenology of seed maturation is important in designing management programs. The present study provides the first quantitative assessment of G. paniculata seed-maturation phenology in a field population, as well as the first quantitative assessment of how the efficacy of herbicide treatment in preventing production of germinable seeds depends on the timing of treatment in relation to this phenology. Seeds were collected from untreated plants on five dates during July and August in both 2016 and 2017 and tested for germinability. Percent germination increased from 20% to 81% between July 22 and 28 and exceeded 90% by August 4, 2016. The seed-maturation phenology in 2017 was similar but delayed by about 4 d. On a growing degree-day scale, seed-maturation phenologies for the 2 yr were nearly identical. We also tested germinability of seeds from plants sprayed with glyphosate (23.4 ml ae L−1) on July 11, 18, and 25, 2016 (one date per plant). Percent germination increased from 0% to 13% to 20% over successive treatment dates, highlighting the importance of completing treatment early in the growing season.

Although introduced pasture grasses are essential for forage production in current livestock farming, some species cause serious impacts on native biodiversity when naturalized. Information on the seed dispersal of invasive forage grasses from cultivated settings to surrounding environments can inform management efforts to prevent their naturalization. In this case study, we quantified the wind-mediated seed dispersal distance and amount of dispersed seed of invasive forage grasses from agricultural grasslands in Hokkaido, northern Japan. In total, 200 funnel seed traps were installed around three regularly mown grasslands and one unmown grassland where various forage grass species were grown in mixture. Seeds of each species dispersed outside the grasslands were captured from May to October 2017. Based on the trapped distances of seeds, the 99th percentile dispersal distance from the grasslands was estimated for six species, including timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.), and Kentucky bluegrass (Poa pratensis L.). For two dominant species, P. pratense and D. glomerata, the numbers of seeds dispersed outside the field under mown and unmown conditions were determined under various plant cover situations. The estimated dispersal distances ranged from 2.3 m (P. pratense) to 31.5 m (P. pratensis), suggesting that areas within approximately 32 m of the grasslands are exposed to the invasion risk of some forage grass species. For both P. pratense and D. glomerata, the number of seeds dispersed outside the unmown grassland exceeded 100 seeds m−2 under high plant cover situations, while the number of seeds dispersed from the mown grasslands at the same plant cover level was less than one-third of that number. The results suggest that local land managers focus their efforts on frequent mowing of grasslands and monitoring of the areas within approximately 32 m of the grasslands to substantially reduce the naturalization of invasive forage grasses.

Skunk-vine (Paederia foetida L.) is an invasive vine native to eastern and southern Asia and is widely distributed in Florida, Hawaii, and other southeastern U.S. states; however, little research has focused on herbicide control. Greenhouse and field experiments were conducted to determine efficacy of aminocyclopyrachlor, aminopyralid, fluroxypyr, glyphosate, imazapic, triclopyr amine, and triclopyr ester at low and high labeled rates when foliar applied to P. foetida at various growth stages in greenhouse experiments. Longer-term control was evaluated in field experiments in central Florida using the same herbicides. PRE herbicides labeled for use in landscape plantings, including dimethenamid-P, flumioxazin, indaziflam, isoxaben, and prodiamine, were also evaluated in greenhouse trials by seeding containers with P. foetida seed. In greenhouse experiments, POST herbicides, including aminocyclopyrachlor, aminopyralid, glyphosate, both triclopyr formulations, and the high rate of fluroxypyr (0.24 kg ae ha−1), provided >90% control across all growth stages at 4 mo after treatment with no regrowth observed. Imazapic provided 49% to 89% control, with efficacy decreasing with P. foetida size, and generally provided less control than other treatments. Field experiments confirmed results from greenhouse studies. In PRE trials, flumioxazin and prodiamine provided better control than all other PRE herbicides evaluated, reducing shoot weights by 99% and 84%, respectively, compared with nontreated controls. Our data suggest all herbicides evaluated POST could potentially be used to manage P. foetida, although less control was achieved with imazapic compared with other herbicides. Further research is needed to determine herbicide efficacy on more mature plants and to develop application methods that would be less injurious to non-target vegetation. In landscapes, flumioxazin or prodiamine could be used for PRE control, but POST options that are labeled for landscape use should be identified in future research.

Minimizing the negative ecological impacts of exotic plant invasions is one goal of land management. Using selective herbicides is one strategy to achieve this goal; however, the unintended consequences of this strategy are not always fully understood. The recently introduced herbicide indaziflam has a mode of action not previously used in non-crop weed management. Thus, there is limited information about the impacts of this active ingredient when applied alone or in combination with other non-crop herbicides. The objective of this research was to evaluate native species tolerance to indaziflam and imazapic applied alone and with other broadleaf herbicides. Replicated field plots were established at two locations in Colorado with a diverse mix of native forbs and grasses. Species richness and abundance were compared between the nontreated control plots and plots where indaziflam and imazapic were applied alone and in combination with picloram and aminocyclopyrachlor. Species richness and abundance did not decrease when indaziflam or imazapic were applied alone; however, species abundance was reduced by treatments containing picloram and aminocyclopyrachlor. Species richness was only impacted at one site 1 yr after treatment (YAT) by these broadleaf herbicides. Decreases in abundance were mainly due to reductions in forbs that resulted in a corresponding increase in grass cover. Our data suggest that indaziflam will control downy brome (Bromus tectorum L.) for multiple years without reduction in perennial species richness or abundance. If B. tectorum is present with perennial broadleaf weeds requiring the addition of herbicides like picloram or aminocyclopyrachlor, forb abundance could be reduced, and in some cases there could be a temporary reduction in perennial species richness.

Glossy privet (Ligustrum lucidum W. T. Aiton) is a highly aggressive tree that has become globally invasive in a wide range of habitats and can quickly form dense thickets, shading and outcompeting native vegetation. Slowly decomposing slash following removal of dense infestations can create additional management challenges, including fire risk concerns, which curtailed planned invasive plant removal projects on certain tracts within the Balcones Canyonlands Preserve near Austin, TX. This prompted a pilot study to explore whether wood-decaying fungi could be used to hasten the recycling of L. lucidum logs back into the forest ecosystem. We inoculated 25 freshly cut L. lucidum logs with Trametes versicolor (Fr.) Pilat at two study sites and monitored the inoculated logs and 5 untreated control logs over a 3-yr period (February 2015 to March 2018). We found that inoculation significantly accelerated wood decay. By the end of our study, 100% of logs with >3 inoculation points were in advanced stages of decay, while only one of the control logs showed noticeable signs of decay. Inoculating logs in the field was easy and suitable for novices, requiring little or no previous experience to achieve successful results. An added benefit of using T. versicolor is its medicinal properties and potential for bioremediation. We have continued to inoculate logs with comparable success and are integrating them into forest restoration projects. Applied on a larger scale, these wood-decaying fungi have the potential to transform nonnative deadwood from a threat to an asset.

Downy brome (Bromus tectorum L., syn. cheatgrass) is a winter annual grass that invades North American cropping, forage, and rangeland systems. Control is often difficult to achieve, because B. tectorum has a large seedbank, which results in continuous propagule pressure. Pyrenophora semeniperda (Brittlebank and Adam) Shoemaker, a soilborne fungal pathogen, has been investigated as a biological control for B. tectorum, because it can kill seeds that remain in the seedbank, thereby reducing propagule pressure. Temperature influences P. semeniperda and has not been investigated in the context of seeds collected from different B. tectorum locations, that may vary in susceptibility to infection. We compared the effects of temperature (13, 17, 21, 25 C) and B. tectorum seed locations (range, crop, subalpine) with different mean seed weights on infection rates of P. semeniperda using a temperature-gradient table. Infection differed by seed location (P < 0.001) and temperature (P < 0.001), with lighter-weight seeds (i.e., range and subalpine) more susceptible to P. semeniperda infection. Infection increased as temperature increased and was higher at 21 C (66.7 ± 6.7%) and 25 C (73.3 ± 6.0%). Germination was affected by seed location (P < 0.001) and temperature (P = 0.019). Germination was highest for the crop seed location (45.4 ± 4.2%) and overall decreased at higher temperatures (21 and 25 C). Our results suggest that B. tectorum seeds from a crop location are less affected by P. semeniperda than those from range and subalpine locations. Moreover, this demonstrates a temperature-dependent effect on all populations.

Radnor Lake State Natural Area in Nashville, TN, has cedar glades that contain the endangered perennial herb wild dill [Perideridia americana (Nutt. ex DC.) Rchb.] and the invasive shrub Amur honeysuckle [Lonicera maackii (Rupr.) Herder]. This research examined whether L. maackii treatment in the Radnor Lake State Natural Area cedar glades is followed by an increase in P. americana plants. A grid of 60 adjacent 2 m by 4 m plots was placed in five cedar glades to encompass the P. americana population. With great care to protect P. americana, the annual treatment for L. maackii was to pull plants ≤1-m tall from the ground; and to cut stems >1-m tall and then treat the stumps with glyphosate. The t-tests of means for the log natural of the number of plants in the 60 plots (significance level of P-value = 0.05) were used to compare pretreatment L. maackii and P. americana counts with posttreatment counts in 2018 and P. americana counts at leaf out and flowering in 2018. The L. maackii population was significantly smaller (P-value < 0.001) in 2018 than pretreatment at all five sites. When pretreatment in 2014 and 2015 was compared with posttreatment in 2018 for the P. americana populations, the increases were significant at the Cheek, Harris 2, Hideaway, and Norfleet sites, but the increase at East Hall Farm was not significant. White-tailed deer (Odocoileus virginianus Zimmermann) trampling was the explanation given for the decreases in P. americana from leaf out to flowering at all five sites in 2018. Browsing was evident only at Hideaway, which had a greater loss for P. americana from leaf out to flowering in 2018 than the combined losses for the Cheek, East Hall Farm, Harris 2, and Norfleet sites. The research informed the creation of adaptive management decisions regarding monitoring and treatment of the invasive species L. maackii for an endangered species.

Biological invasions are one of the grand challenges facing society, as exotic species introductions continue to rise and can result in dramatic changes to native ecosystems and economies. The scale of the “biological invasions crisis” spans from hyperlocal to international, involving a myriad of actors focused on mitigating and preventing biological invasions. However, the level of engagement among stakeholders and opportunities to collaboratively solve invasives issues in transdisciplinary ways is poorly understood. The Biological Invasions: Confronting a Crisis workshop engaged a broad group of actors working on various aspects of biological invasions in Virginia, USA—researchers, Extension personnel, educators, local, state, and federal agencies, nongovernmental organizations, and land managers—to discuss their respective roles and how they interact with other groups. Through a series of activities, it became clear that despite shared goals, most groups are not engaging with one another, and that enhanced communication and collaboration among groups is key to designing effective solutions. There is strong support for a multistakeholder coalition to affect change in policy, public education/engagement, and solution design. Confronting the biological invasions crisis will increasingly require engagement among stakeholders.