Introductions of new crops can provide alternate market opportunities, but also pose ecological risks. New crops lack established management, have uncertain performance issues, and may become weedy in their introduced region. The introduction of hemp (Cannabis sativa L.) into southern Florida poses a unique introduction scenario because of the subtropical climate and no commercial production on record, unlike in other eastern and midwest United States. We assessed escape from cultivation for hemp by tracking establishment and reproduction of volunteer plants from the earliest modern hemp planting in Florida. Hemp is a weed across much of the United States matching its historical distribution and has been assessed to be of high invasion risk for Florida because of its biological attributes, history of escape, and colonization in other states and countries. We conducted monitoring of volunteer plants and a seed establishment experiment in southern Florida and found that hemp volunteer plants occurred in pulses over time, with variable and declining germination. Volunteer plants persisted for up to two years and appeared in areas that were disked and mowed according to USDA approved hemp crop termination procedures. In the seed establishment experiment, we found that hemp established in disturbed soils (∼9% of seeds planted) and that mean plant heights and seed counts were positively related to soil disturbance and nutrient addition. These findings show that hemp plantings should be monitored for volunteer establishment, and containment plans should be in place to control the establishment of volunteer hemp plants in agricultural fields. Our study further illustrates the need for multi-year monitoring and repeat termination procedures to ensure containment of hemp volunteers. There was limited evidence of volunteer establishment in surrounding areas and on undisturbed land. However, seed containment, equipment cleaning, and the monitoring of nearby fields and seed transportation routes remains warranted.

Cophinforma spp. are gall-inducing fungi that can infect the highly invasive Brazilian peppertree, Schinus terebinthifolia Raddi, in its introduced range in southern Florida, USA. A classical biological control agent, the thrips Pseudophilothrips ichini (Hood), has been released to mitigate the invasive potential of S. terebinthifolia. We investigated the synergistic potential of thrips feeding damage and gall formation on S. terebinthifolia management program success. A group of potted S. terebinthifolia saplings was inoculated with Cophinforma. Galled, symptomatic and ungalled, asymptomatic saplings were then paired in laboratory cages for a two-choice test with 40 P. ichini adults. Galled and ungalled plants were assessed for dead stem tips and necrotic stem tissue, with and without thrips present. Larval F1 thrips were also counted on each plant. Thrips feeding damage significantly increased the number of dead tips and extent of stem necrosis. Regardless of thrips presence, stem tip mortality and extent of necrosis were not significantly different between galled and ungalled plant pairs. Additionally, the maximum number of F1 larvae counted on stems did not differ between those on galled versus ungalled plants. Gall growth on heavily thrips-damaged plants nearly stopped while galls continued to grow on plants with little thrips damage. While our results suggest the Cophinforma galls do not impact damage potential or plant preference from P. ichini, more work is needed to understand other factors that may contribute to at least additive impacts on S. terebinthifolia in the field, such as more advanced stages of the fungal infection on mature plants and prolonged thrips feeding damage.

Boneseed (Chrysanthemoides monilifera subsp. monilifera; syn Osteospermum moniliferum subsp. moniliferum), is a perennial shrub native to the south-western and southern coasts of South Africa. It was introduced to Australia in about 1852 and now represents a significant threat to natural ecosystems. Despite being listed as a Weed of National Significance, momentum on improving boneseed management has dissipated at a national level, beginning in 2008 (when a national research initiative finished) and increasingly after 2013 (when funding for national coordination ceased). A recent synthesis of past management for boneseed and recommendations for guiding future priorities has rekindled interest in Western Australia. To complement this synthesis and to identify improvements for program efficiency or effectiveness, we reviewed research and management findings on this weed with a focus on the past two decades. We collated information across the ecology and biology of boneseed, and the near relative, bitou bush, as well as useful insight from boneseed management programs applied elsewhere. As part of this review we assessed the classical biological control work that has been done on boneseed, focusing on likely explanations for why, despite nine agents and a naturalised fungus, biological control is not an effective management tool. Our synthesis suggests that for the limited populations with low abundance plants in Western Australia, eradication from the state remains a realistic target. This objective, however, needs to build on the collated baseline of past management efforts and deploy a carefully planned management program over the coming two decades. Systematic surveillance using the latest techniques, combined with manual or herbicide removal and controlled burns where possible, remain the most suitable methods to deploy. The long-lived soil seedbank requires detailed monitoring following initial plant removals and long-term funding to ensure the sustained effort required to deliver the goal of eradication for boneseed in Western Australia.

Whilst invasive plants can modify community and ecosystem attributes, there is little information on their impact across different trophic levels. Here, we examined the effects of Gunnera tinctoria Molina (Mirb.; Gunneraceae; “Chilean-rhubarb”) on the soil detrital food chain, the major pathway for energy flow in terrestrial ecosystems and the recycling of nutrients. Measurements of soil physio-chemistry properties and the natural abundances of C and N isotopes, along with assessments of microbial and earthworm populations were used to verify if G. tinctoria drives the soil food web and how C is transferred from decomposing litter to worm populations. Based on the C isotope compositions of plant material and detritivorous worms (i.e., earthworms and enchytraeid worms), all worms contribute to G. tinctoria litter decomposition, irrespective of their feeding preference. The increased role of larger earthworm populations in litter decomposition was also associated with changes in the soil microbial community, with some bacterial genera being absent from invaded areas. Of particular interest was a three-fold increase in Nitrospira spp. in invaded areas, likely due to an increase in earthworm-related ammonia production, with this being rapidly converted to nitrate. Given the poor representation of other ammonia and nitrite oxidizing soil bacteria, many of the Nitrospira spp. present in invaded soils may perform complete ammonia oxidation (i.e., COMAMMOX). Our results indicate a greater role for native earthworms in decomposition processes in areas invaded by G. tinctoria, resulting in modifications in the other soil biota and an increase in soil nitrate.

An online survey was distributed to South Dakota stakeholders to understand how noxious weeds are currently being managed. The response rate was 26%; 129 stakeholders completed the survey of the 491 stakeholders who opened the survey. Eighty percent of respondents stated noxious weeds were a problem. Canada thistle (Cirsium arvense), leafy spurge (Euphorbia esula) and absinth wormwood (Artemisia absinthium) were the most common and troublesome but all statewide noxious weeds were reported. Herbicides alone (25%) was the most common singular response to manage noxious weeds, but respondents utilized two (27%) to three (24%) other tactics as well. Most respondents (47%) were somewhat satisfied with management tactics while others were completely satisfied (9%), neither satisfied nor dissatisfied (20%), somewhat unsatisfied (11%), or very unsatisfied (15%). A covariate analysis showed that the more management tactics a stakeholder utilized, the less satisfied they were with control (P < 0.0001). The most common barrier of adopting new tactics was effectiveness (26%) followed by a combination of effectiveness + current production practices + cost + labor (13%). An additional covariate analysis showed that the increase of management tactics increased the barriers of adoption (P = 0.04) and increasing the number of barriers of adoption resulted in stakeholders being dissatisfied with control (P = 0.0003). Overall, the results of the survey suggest that statewide noxious weeds remain a problem, and multiple tactics are used to manage these weeds. However, Extension efforts need to address how to use current and implement new management to increase effectiveness.

We report a pair of simple PCR-RFLP assays based on two independently segregating nuclear genes which can differentiate North American native Phragmites australis subsp. americanus Saltonst., P.M. Peterson & Soreng from other lineages. Because nuclear markers are inherited biparentally, researchers can also use them to screen for F1 hybrids between americanus and the other lineages. We show that a previously described assay based on an indel in the nuclear gene NRT2 consistently identifies a wide range of americanus haplotypes and distinguishes them from the Gulf Coast type Phragmites australis (Cav.) Trin. ex Steud. ssp. berlandieri (E. Fourn.) Saltonst. & Hauber. We also demonstrate a new PCR-RFLP assay for a previously described diagnostic single nucleotide polymorphism adjacent to the PaGT4 microsatellite marker which also distinguishes americanus from the other lineages. In addition, we report the first case of Asian haplotype AS identified in North America and make recommendations for its detection. Our findings expand the tools available to those monitoring for invasion by introduced Phragmites in North America.

Invasive common reed, Phragmites australis ssp. australis ((Cav.) Trin. ex Steud.) has established and dominated Ontario wetlands for decades. The detrimental effects of P. australis invasions on wetland habitats have demanded intervention through aggressive suppression efforts. However, constraints in available control methods to suppress P. australis have led to persistent invasions. To improve P. australis management in wetlands, we investigated remotely-piloted aircraft systems (RPASs) as a precision tool for herbicide application. We applied an imazapyr-based herbicide (240 g active ingredient L-1) with a spray-equipped RPAS at selected test sites, marking the first-ever application of its kind in Canada. We evaluated 1) the efficacy of RPAS-based herbicide application to P. australis and 2) examined the plant community changes one year after the initial herbicide application. We found a > 99% reduction in live P. australis stems, along with reductions in species richness (33%), Shannon-Weiner diversity (73%), Simpson’s reciprocal diversity (50%), and Pielou’s evenness (73%) in the year following herbicide application. Plant community changes varied by field site; one wetland underwent a secondary invasion by European Frog-bit (Hydrocharis morsus-ranae (L.)) while the other was dominated by the native Spotted Jewelweed (Impatiens capensis (Meerb.)), highlighting the complexities of plant community succession following herbicide application in biodiverse wetlands.

Basal bark application involves applying an oil-soluble herbicide in an oil carrier to the lower 0 to 45-cm of woody stems. For triclopyr, basal bark application typically requires the butoxyethyl ester formulation; however, this cannot be applied when standing water is present, which is common in seasonally flooded wetlands. Recently, the intermediate oil and water-soluble triclopyr acid formulation was registered for use in aquatic sites, allowing for basal bark applications in wetlands where standing water is present. Recent studies indicated that flooding after basal bark treatment can result in triclopyr release to surface waters and subsequent non-target injury. Elevated band application height (i.e., treating a higher band on each stem) may reduce non-target injury potential; however, this modified application technique has not been well tested on woody invasive species. To evaluate this approach, a field study on Schinus terebinthifolia was conducted near Melbourne and Wimauma, FL on well-established and juvenile rootstocks. Treatments included triclopyr acid at 17, 34, and 69 g L-1 applied in an oil carrier and treatment band heights of 0 to 45-cm and 61 to 107-cm from the ground line. At Melbourne, both band heights treated with 34 or 69 g L-1 resulted in 75 to 100% mortality of mature rootstocks. However, triclopyr applied at 17 g L-1 to the low and elevated band heights resulted in 70 and 11% mortality, respectively. All treatments resulted in 90 to 100% mortality at Wimauma, where the rootstocks were juvenile and much smaller. These findings indicate elevated band heights may be a useful approach for woody plant control and may support an effective management strategy in inundated wetlands that provides better prevention of non-target injury.

Invasive plants’ ability to extend their range depends upon their local environment and both positive and negative interactions with native species. Interactions between invasive and native plants may be indirectly linked to the soil fungal community, which may enhance or suppress invasion through mutualism or parasitism. Many invasive plants preferentially select fungal communities or change soil chemistry to gain a competitive advantage, and such changes can remain even after the invader is removed, known as legacy effects. Linaria vulgaris is an invasive forb that is aggressive in the Western U.S. but is non-aggressive in the Midwestern U.S. We evaluated the relationship between soil abiotic properties, nitrogen (N) enrichment, arbuscular mycorrhizal fungal (AMF) community composition and L. vulgaris invasion in aggressive (CO) and non-aggressive (IL) populations. We collected soil from uninvaded and invaded sites in Gothic, CO, and near Chicago, IL, and sequenced AMF community composition in each site. Using the same soil, we grew L. vulgaris and native species for 120 days, with half of pots receiving N-fertilization, and harvested biomass. We also injected a 15N-labelled tracer in pots and analyzed plant tissue for 15N enrichment and N uptake rates (NUR). In CO soil, L. vulgaris rhizomes sprouted more in invaded soil, whereas in IL soil, L. vulgaris only sprouted in uninvaded soil. N-fertilization had no impact on biomass and NUR did not differ significantly between any treatment. AMF communities differed between the two sites but were not significantly influenced by invasion history. Our results suggest that L. vulgaris leaves legacy effects, but that these effects are different between aggressive and non-aggressive populations. Legacy effects may facilitate reinvasion in CO, but we did not find conclusive evidence of legacy effects in IL, and differences between the sites could be shaped by endemic AMF communities.

Tree-afflicting pests, such as insects and pathogens, could change forests in ways promoting invasions by non-native plants. After tree death associated with the fungal pathogen oak wilt (Bretziella fagacearum (Bretz) Z.W. de Beer, Marincowitz, T.A. Duong & M.J. Wingfield) and its attempted containment (severing root connectivity and sanitation removal of infected trees), we examined change in cover of the non-native liana Oriental bittersweet (Celastrus orbiculatus Thunb.; hereafter Celastrus) at 28 sites in temperate black oak (Quercus velutina Lam.) forests, Ohio, USA. During our five-year study spanning 2020 to 2024, Celastrus cover increased significantly (P < 0.05) through time at oak wilt sites but not in untreated reference forest sites without evidence of oak wilt. Celastrus cover increased by an order of magnitude, up to an average of 32× among oak wilt treatments up to 10 years old. By 2024, Celastrus cover ranged from 6-22% on average in 5-10-year-old oak wilt treatments, compared with 1% cover in reference forest. Results indicate that non-native plant invasion accelerated following disturbance associated with a fungal pathogen and its attempted containment, and more generally, suggest that tree-afflicting pests can promote invasive plants in forests. Co-management of tree-afflicting pests and non-native plants may become increasingly important to ensure forests recovering from tree mortality are dominated by native plants.

Amur honeysuckle (Lonicera maackii) is an aggressive invader of forests throughout the eastern United States. While self-pollination has been identified as an important trait of invasive plant species, this trait is understudied, and Amur honeysuckle is anecdotally described as lacking this characteristic. To examine the ability of Amur honeysuckle to self-pollinate, we selected 171 individual shrubs distributed across nine sites. Each site was grouped into one of three invasion types: heavy, light, and sprouting (sites on which a basal cutting treatment previously occurred, but Amur honeysuckle was allowed to reestablish). We compared the number of berries, seeds per berry, and seed germination rates of self- and open-pollinated flowers by pairing branches covered with pollination bags prior to flower emergence with uncovered branches on the same individual shrub. Out of 171 individuals, 48 produced berries from self-pollination within pollination bags (28%), with 48% of bagged branches exhibiting some degree of necrosis or chlorosis, presumably due to increased temperature and humidity. Berries from self-pollination produced 1.5 ± 1.4 (mean ± 1 SD) seeds per berry, whereas berries resulting from open-pollination produced 3.3 ± 1.5 seeds per berry. In a germination trial, 47.3% of self-pollinated seeds germinated, compared to 41.7% of open-pollinated seeds. This study has shown that Amur honeysuckle can self-pollinate and set viable seed, providing the species with an important mechanism to increase population abundance during the early stages of invasion.

Several Elaeagnus species (autumn olive [E. umbellata (Thunb.)], Russian olive [E. angustifolia (L.)], and thorny olive [E. pungens (Thunb.)]) are invasive in North America. Elaeagnus pungens is prevalent throughout much of the southeastern United States, commonly overtaking wooded and natural areas, bottomlands, and roadsides. While many management methods including several herbicide treatments have been evaluated, efficacy of these methods can vary based on the size and density of the target plants. Further, personal communication with land managers revealed a lack of information that incorporated application effort, duration and associated cost into treatment efficacy and usefulness. We evaluated three herbicide application methods using the free acid formulation of triclopyr in an E. pungens infested forest in South Carolina, United States to determine the effectiveness of each application method. We estimated pre-treatment E. pungens biomass and destructively harvested all live material post treatment to obtain actual biomass values. Foliar herbicide application was ineffective, but both cut stump and basal bark application nearly eliminated E. pungens in the treatment plots. The basal bark application took slightly more time to complete than cut stump treatments but was described as less physically demanding by applicators. Based on treatment efficacy and time required, the basal bark application method seems most prudent for controlling E. pungens in these areas. These results will help land managers more effectively use their resources for invasive woody plant control.