Regularly mown road verges are an important habitat for conservation of grassland vegetation. Disturbance and movement of seed-contaminated soil during road construction and maintenance makes road verges susceptible to the establishment of invasive alien plants such as garden lupine (Lupinus polyphyllus Lindl.). To combat the spread of L. polyphyllus via seeds, we tested methods for seed destruction using heat. This study aimed at developing heat eradication methods for dry and imbibed L. polyphyllus seeds applying dry heat (88, 93, 98, 103 C for 1, 3, 5, 10 min) in a laboratory, steam (85, 90, 95 C for 3, 5, 10 min) in a test box steaming device, and (97 C at 10 to 17 min; dry seeds only) in a stationary soil-steaming machine (S30). To speed up water absorption and posttreatment germination, the imbibed seeds were manually scarified before the heat treatment and the dry seeds afterward. Additionally, germination of two seed batches of different ages was tested applying dry heat (88, 98 C at 3, 5 min). Steam treatments inhibited seed germination more than dry heat in both dry and imbibed seeds. Germination dropped to <5% when steamed at ≥90 C or dry heated at >100 C. Seed germination decreased with higher temperatures and longer exposure times. Imbibed seeds exhibited lower germination compared with dry seeds for dry and steam heat. Approximately 0.5% of dry seeds germinated when steamed using the S30. The seeds collected in 2022 were less sensitive to dry heat than seeds from 2020. In conclusion, hot steam is more effective in reducing L. polyphyllus seed germination than dry heat. Thus, to successfully eradicate L. polyphyllus seeds in soil masses, we recommend steaming them at 97 C for at least 10 min.

Basal bark treatment with triclopyr butoxyethyl ester is used to control woody invasive plants, including Brazilian peppertree (Schinus terebinthifolia Raddi). However, the ester formulation cannot be applied where standing water is present, which includes wetlands where S. terebinthifolia is found. In 2009, a low-volatile acid formulation of triclopyr was labeled for use in aquatic sites, which allows for basal bark applications when standing water is present. This formulation may have utility for controlling woody plants in standing water. However, anecdotal observations of injury to non-target plants following applications during periods of inundation have been reported. To address this, mesocosm studies were conducted to assess non-target injury through triclopyr root exudation or release from the surface of treated stems via flooding. Mesocosms contained S. terebinthifolia as the treated target, while sugarberry (Celtis laevigata Willd.), buttonbush (Cephalanthus occidentalis L.), and red maple (Acer rubrum L.) were included as non-targets. In the first study, the pathway of root exudation for non-target injury following triclopyr (34 g L−1) basal bark application was isolated with activated charcoal placed at the soil surface. In the second study, mesocosms were flooded to assess triclopyr release from the surface of treated stems and subsequent non-target injury. Defoliation of non-target species posttreatment was ≤8%, and triclopyr was detected at ≤5 µg L−1 in mesocosm wells when activated charcoal was present. Posttreatment non-target defoliation up to 92%, coupled with triclopyr concentrations in surface waters and wells as high as 4,637 µg L−1, indicated triclopyr movement as a result of flooding. Additionally, triclopyr non-target injury from soil activity independent of flooding was observed. These findings provide limited evidence of triclopyr root exudation but considerable evidence of triclopyr release during flooding following basal bark treatment and support a cautionary approach to basal bark application when standing water is present.

Invasive species pose a threat to the livelihoods of many people living on rangelands of the western United States. Invasive species impact many ecosystem goods and services of the areas they invade and represent one of the largest causes of habitat degradation. On private ranches, economic analyses often find that conservation practices, such as invasive species control, are not economically viable, in contrast to what is found at the landscape scale. In northeast Wyoming, ventenata [Ventenata dubia (Leers) Coss.] is a relatively new invader in the Great Plains ecoregion that threatens forage production on ranches. Our objective was to explore the economic costs of V. dubia for two options available to a ranch operation: purchasing extra hay to offset losses in forage and controlling V. dubia with herbicide. Using a partial budget analysis, we compare these two options in three invasion scenarios using a range of forage utilization rates and discount rates. Controlling V. dubia with herbicide was a cheaper option compared with purchasing additional hay in many cases. In fact, at 50% utilization, it is cheaper to control V. dubia in all of our scenarios at all discount rates given our assumptions. For lower grazing utilization rates, it becomes cheaper to purchase hay in some cases other than in our worst-case invasion scenario. In these cases, coordination among ranchers is needed to effectively control V. dubia. There are many ranch-specific differences that may make a different option more feasible, and we did not explore options of reducing herd sizes. However, our results suggest that controlling V. dubia can be an economically viable option under certain circumstances. Additional assistance in the form of a cost-share program, and facilitation of coordination is needed to overcome the difficulties of private management of invasive species.

Sulphur cinquefoil (Potentilla recta L.) is an invasive plant of concern within grasslands in western North America. To better understand the role of native plant communities and soil seedbank in P. recta invasion within grasslands, we conducted two greenhouse studies to examine (1) P. recta growth response when grown with and without fertilizer in established native plant communities of varying functional groups (grasses, forbs, or grasses and forbs), and (2) the prevalence of P. recta and other species in the soil seedbank at varying soil depths (0 to 5 cm, 5 to 10 cm, 10 to 15 cm) of grasslands invaded by P. recta in southeastern British Columbia, Canada. The growth response of P. recta did not differ between the native plant communities. However, P. recta above- and belowground biomass declined as native plant aboveground biomass increased, suggesting a productive plant community may be important to suppress P. recta. Fertilizer did not affect the growth response of P. recta or native plants, suggesting nutrients may not have been a dominant limiting factor under greenhouse conditions. Nine species were identified in the soil seedbank. Seven were nonnative, which included P. recta, and native species represented less than 2% of the seedbank. Of the average number of emerged nonnative seedlings, more than 20% were P. recta. The number of emerged P. recta seedlings was 69% lower at 10- to 15-cm compared with 0- to 5-cm soil depth, although the successful germination of P. recta at greater soil depths suggests viable P. recta seeds are persisting in the seedbank. Active revegetation may be an important strategy to mitigate P. recta reinvasion or secondary invasion by other invasive species from the soil seedbank.

Sulphur cinquefoil (Potentilla recta L.) is an invasive perennial forb threatening rangelands in western North America. To identify best management strategies to control P. recta, we examined targeted goat (Capra hircus L.) grazing conducted once (pre-flowering) versus twice (pre-flowering and flowering and seed set), aminopyralid application, and integrated targeted grazing and aminopyralid as management strategies. We also examined the interaction between treatments and seasonality (spring and summer) and explored the possibility of off-target effects to non-target species. Two intermountain rangelands in British Columbia, Canada, were treated, one with targeted grazing treatments only and one with targeted grazing and herbicide treatments. Targeted grazing treatments were implemented in 2019 and 2020, and aminopyralid was applied once in 2019 at a rate of 56 g ai ha−1. Potentilla recta aboveground biomass and number of seed heads declined following targeted grazing treatments at both field sites in 2019 and 2020 when compared with the control, with no differences between targeted grazing treatments. In May 2020, before the implementation of targeted grazing for the second year, a decrease in P. recta biomass was not measured in the targeted grazing treatments, but biomass was 87% to 99% less in the herbicide-only and targeted grazing plus herbicide treatments. In July 2020, declines in biomass and seed heads in the herbicide-only and targeted grazing plus herbicide treatments did not differ from grazing twice, and aminopyralid effects did not differ among the three herbicide treatments. Further research is required to examine legacy effects of targeted goat grazing and aminopyralid on P. recta, establish reapplication frequency of treatments, and determine whether integrating targeted goat grazing and aminopyralid is needed in the long term to manage P. recta. A long-term study is also needed to examine off-target effects from targeted goat grazing and aminopyralid and ways to mitigate these effects to promote healthy native rangeland plant communities.

Individual plant treatment (IPT) techniques (e.g., basal bark, cut stump, hack and squirt) are used for woody invasive plant management and often rely on small trigger-pump spray bottles as an economical and efficient way to deliver a herbicide to the target species. Worldwide, plastic suppliers produce many models and designs with a wide range of uses, including pesticide application. However, spray bottle performance has rarely been examined in relation to IPT techniques for operational invasive plant management. We tested 10 commonly available spray bottles for trigger output and variation over repeated strokes. We also examined sustained trigger sprayer performance over a 6-wk period for spray bottles containing water or basal oil carriers blended with amine and ester formulations of triclopyr, respectively. In the first study, we found significant differences in spray output per stroke between almost every bottle tested. Almost all spray bottle brands yielded outputs greater than 1.0 ml per stroke, which exceeds the maximum application amount specified for hack and squirt. Several bottles produced an output of greater than 2.5 ml per stroke. In the second study, the output per stroke was reduced for basal oil mixes, with significant reductions measured for two brands by 21 d and for all three brands tested by 42 d after mixing. These results indicate that consumer-grade trigger sprayers are likely to depreciate rapidly with routine operational use without proper hygiene maintenance. Even then it is likely that these application devices may need to be replaced several times annually. Trigger-pump spray bottles are an economical and practical solution for remote field operations and volunteer weed control activities. These sprayers are most suitable for spray-to-wet techniques such as basal bark and cut-surface treatments but may potentially be less suited for hack and squirt application, which often requires sub-milliliter precision.

Exotic conifers are rapidly spreading in many regions of New Zealand, as well as in many other countries, with detrimental impacts on both natural ecosystems and some productive sector environments. Herbicides, in particular the active ingredient triclopyr, are an important tool to manage invasive conifers, yet there is a paucity of information that quantifies the amount of herbicide required to kill trees of different sizes when applied as a basal bark treatment. Two sequential experiments were conducted to define the amount of triclopyr required to kill individual invasive lodgepole pine (Pinus contorta Douglas ex Loudon), trees of different sizes when applied in a methylated seed oil to bark (either the whole stem or base of the tree) and to determine which tree size variates (height, diameter at breast height [DBH], crown diameter [CD]) or derived attributes (crown area, crown volume index) best characterized this dose–response relationship. The outcomes of the dose–response research were compared with field operations where triclopyr was applied to the bark of trees from an aerial platform. Applying the herbicide to the whole stem, as opposed to the base of the tree only, significantly increased treatment efficacy. The tree size variates DBH, CD, crown area, and crown volume index all provided good fits to the tree mortality data, with >91% prediction accuracy. Of these variates, CD provided the most practical measure of tree size for ease of in-field calculation of dose by an operator. Herbicide rates used in field operations were seven to eight times higher than lethal doses calculated from experimental data. Our results highlight the potential for substantial reductions in herbicide rates for exotic conifer control, especially if dose–response data are combined with remotely sensed quantitative measurements of canopy area or volume using new precision technologies such as unmanned aerial vehicles.

Garden loosestrife (Lysimachia vulgaris L.), is an invasive wetland plant that is subject to management in King County, WA, USA. Large-scale management efforts are generally conducted using herbicides. In this case study, we analyzed 17 yr of monitoring and treatment data in four riparian areas in King County to estimate the rate of spread of L. vulgaris and the efficacy of herbicidal treatments against L. vulgaris populations. In each area, herbicide treatments were applied annually. In three of the areas, the area infested with L. vulgaris did not change over time, while in the fourth area populations of L. vulgaris were spreading at a rate of 0.79 m2 yr−1. There were a greater number of sampled locations infested with L. vulgaris over the 17-yr period, and because populations were either not spreading or spreading slowly, it is possible that populations were becoming more fragmented. There was no relationship between the percentage of the infested area treated with herbicides and the area infested in the following year. However, there was a negative relationship between the area treated and the percent change in the invaded area; specifically, in years when <80% of the infested area was treated, there was an increase in the percent change of the invaded area between the year of treatment and the following year. The results of this study suggest that at the current level of management effort, the spatial extent of L. vulgaris did not retract over the 17-yr study period.

To successfully reduce overall invasive plant cover over time, an effective treatment plan must be established such that mortality exceeds new colonization and resprouting growth rates. However, few evaluations of the effects of long-term, consistent treatment at different intervals exist. We report the effects of treatment intensity on Old World climbing fern [Lygodium microphyllum (Cav.) R. Br.], Brazilian pepper (Schinus terebinthifolia Raddi), and punktree [Melaleuca quinquenervia (Cav.) S. F. Blake] as part of a large restoration project that has been underway for 6 yr in Telegraph Swamp at Babcock Ranch Preserve, a 27,520-hectare (68,000-acre) conservation area in Florida, USA. We found that at the end of the 6-yr period, for all three species, average live cover did not exceed 5% across all transects. In addition, dead foliar cover was higher than live cover for all three invasive plants, indicating progress toward restoration goals. We also found that percent live cover of L. microphyllum was significantly reduced only after four or more treatments were applied during the 6-yr period, as opposed to when three or fewer treatments were applied. Reductions in percent cover of live foliage were apparent only when the treatments were applied more often than biennially, as opposed to less often than biennially. Additionally, we found higher L. microphyllum cover in clear-cut and replanted cypress stands than in natural stands. Based on these findings, we conclude that treatments applied four or more times, or more often than biennially, were more effective at significantly reducing advanced invasions of L. microphyllum, S. terebinthifolia, and M. quinquenervia, especially where previous management activities or their effects may have increased the cover of invasive plants.

The Appalachian region of the United States is home to the largest temperate deciduous forest in the world, though surface mining has caused significant forest loss. Many former coal mines are now dominated by invasive plants, which often inhibit establishment of desirable species, especially slower-growing native trees. Autumn-olive (Elaeagnus umbellata Thunb.) is a nonnative, nitrogen-fixing shrub that was historically planted on former coalfields, but now impedes reclamation. To better understand the influence of E. umbellata management practices on hardwood establishment, we evaluated two common management practices: cutting and cut stump herbicide treatment. Planted native tree species, including black cherry (Prunus serotina Ehrh.), pin oak (Quercus palustris Münchh.), and red maple (Acer rubrum L.), were monitored for survival and performance over two growing seasons following E. umbellata removal. In each plot, we also measured plant-available nitrate (NO3−) and ammonium (NH4+) in soils using ionic exchange membranes. At the end of the first growing season, native tree survival was high, and the presence or absence of E. umbellata had little effect on tree survival or growth, despite the higher plant-available nitrate where E. umbellata was present. By the end of the second growing season, native tree survival dropped to 20% to 60% and varied among E. umbellata treatments. Survival was highest when E. umbellata was cut and treated with herbicide, though tree growth was similar across all treatments without E. umbellata. When establishing native trees to replace E. umbellata, cutting and herbicide application treatment of the invader resulted in the highest overall efficacy (100% control), though the most cost-effective method may be to simply cut mature stands despite regrowth, as this resulted in equivalent native tree growth over 2 yr. While this allowed E. umbellata regeneration, it provided sufficient invader control to allow initial tree establishment. Cutting and herbicide application treatment resulted in less E. umbellata regeneration and appears to provide greater assurance that established trees will persist over the long term.

Prescribed burning and the herbicide clopyralid are very effective tools for the management of yellow starthistle. However, repeated use of either can be impractical or can present other problems. The potential solution is the development of an effective integrated weed management strategy using a combination of the two approaches. In small plot studies (0.2 ha), we tested one of five possible treatments: (1) untreated control, (2) 2 consecutive yr of clopyralid (0.105 kg ha−1), (3) 2 consecutive yr of prescribed summer burning, (4) first-year clopyralid followed by second-year prescribed burning, and (5) first-year prescribed burning followed by second-year clopyralid. Treatments were made in 1999 and 2000 at three study sites in California (San Benito, Yuba, and Siskiyou counties). In 2001, the year following the final treatment, 2 consecutive yr of clopyralid or first-year burning followed by second-year clopyralid consistently reduced yellow starthistle cover in the following year by 92 to 100%. However, at the Yuba site, clopyralid alone increased medusahead and ripgut brome cover. Although 2 consecutive yr of burning was effective in Yuba, very high levels of starthistle infestation in San Benito were not completely burned in the second year because of the lack of available consumable fuel. Clopyralid treatment the first year followed by prescribed burning in the second year stimulated yellow starthistle germination and did not reduce the infestation. In a large-scale study conducted at two sites (13 and 81 ha) in southern Monterey County, we used a first-year burn followed by either 2 yr of clopyralid (0.158 kg ha−1) or a single year of clopyralid (0.210 kg ha−1) and a subsequent burn. Results were in close agreement with those found in the small-scale studies. In the year following the final treatment, control of yellow starthistle was greater than 99% when the burn was followed by 2 yr of clopyralid. In contrast, when a prescribed burn was used in the last year of the program, the level of control was not as good, probably because of the increased germination of the remaining soil seedbank. These results indicate that a first-year prescribed burn followed by a second-year clopyralid treatment can provide consistently good control of yellow starthistle, as well as reduced levels of noxious annual grasses, including medusahead and ripgut brome.

Students studying weed science would expand their knowledge by conducting targeted experiments on invasive weeds. Tamarix spp., some of the most problematic weeds known in the United States, have value for weed science education. Tamarix was used in an undergraduate laboratory course to demonstrate weed science principles for a minimal cost and with great potential for academic enhancement. The laboratory exercise was designed to teach weed science students about the difficulty associated with controlling invasive weeds even at a relatively young age in a region where plants have been detected but large-scale invasion has not occurred to emphasize the importance of early detection and rapid response. The successful execution of this exercise and the positive student response suggests that Tamarix and other weeds with similar reproductive capacities could be valuable additions to weed science curricula. Innovative approaches to teaching weed science facilitate greater learning of this complex subject by students from diverse backgrounds and academic disciplines.

Developing ecological principles applicable to invasive plant management is central to implementing sustainable strategies. We tested portions of a potentially useful successional-based management framework to further our understanding of the relationship between disturbance and colonization during revegetation of invasive weed-dominated grasslands. We hypothesized (1) intermediate wheatgrass density and biomass would be greatest at highest seeding rates, (2) control and tillage procedures that increase the availability of safe sites would increase wheatgrass abundance, and (3) spotted knapweed density and biomass would be lowest in treatments with highest wheatgrass density and biomass. Treatments included three disturbance levels: (1) no disturbance, (2) application of glyphosate, and (3) fall tillage. Colonization treatments were seeding intermediate wheatgrass of 0, 500, 2,500, and 12,500 seeds m−2. Treatments were factorially applied in a randomized complete-block design with four replications at each of two sites located in Montana. Density and biomass of intermediate wheatgrass and spotted knapweed were sampled in 1997 and 2001. At both sites, seeding 2,500 or 12,500 seed m−2 increased wheatgrass density over that of the nonseeded control in 1997. The highest seeding rate produced almost three times as many wheatgrass plants as 2,500 seeds m−2 that year. By 2001, only the highest seeding rate produced wheatgrass densities greater than that of the nonseeded control at Bozeman. Seeding rates higher than 500 seeds m−2 yielded greater wheatgrass biomass than the nonseeded control with or without either tillage or glyphosate. At the highest seeding rate, tillage or glyphosate doubled intermediate wheatgrass biomass compared with no disturbance. Spotted knapweed generally had lower biomass where intermediate wheatgrass density and biomass was highest. One approach to rehabilitation is to design disturbances that favor desired species and then use high seeding rates that overwhelm the pool of available propagules and occupy a high percentage of safe sites.

The distribution and abundance of invasive species can be strongly influenced by habitat suitability and by corridors that facilitate dispersal. We synthesize results from a large-scale invasive plant survey with a patch-scale expansion experiment. The large-scale survey involved transects up to 250 m away from of all roads in a 32,000 ha forest. The patch experiment involved initiating invasions in different habitat types (roadside, wetland, disturbed, and intact forests), and then fitting statistical models to patch spread rates. The large-scale survey highlighted the importance of roads in predicting the presence of invasive plants, also revealing that one invasive plant, Microstegium vimineum, has spread rapidly since its purported introduction in 1994. The patch-scale experiments focused on Microstegium and demonstrated that spread rates are higher in roadsides than in forested and wetland patches, even in the absence of major disturbances. These results highlight the importance of landscape features when designing prevention and management practices aimed at limiting invasive plant abundance and spread.

Common reed (Phragmites australis) is an invasive perennial grass in aquatic and riparian environments across the United States, forming monotypic stands that displace native vegetation that provides food and cover for wildlife. Genetic variation in global populations of common reed has given rise to two invasive haplotypes, I and M, in the United States. Our objectives were to (1) determine if any differences in herbicide efficacy exist with respect to common reed haplotypes I and M and (2) screen for other labeled aquatic herbicides that may have activity on common reed haplotypes I and M, most notably imazamox and diquat. A replicated outdoor mesocosm study was conducted in 1,136-L (300-gal) tanks using haplotypes I and M of common reed. Restriction fragment length polymorphism methodologies were used to verify the identification of I and M haplotypes used in this study. Diquat at 2.2 (1.9) and 4.5 (4.0) kg ai ha−1 (lb ai ac−1), glyphosate at 2.1 (1.8) and 4.2 (3.7) kg ae ha−1 (lb ae ac−1), imazamox at 0.6 (0.5) and 1.1 (0.9) kg ai ha−1 (lb ai ac−1), imazapyr at 0.8 (0.7) and 1.7 (1.5) kg ai ha−1 (lb ai ac−1), and triclopyr at 3.4 (3.0) and 6.7 (5.9) kg ae ha−1 (lb ae ac−1) were applied to the foliage of common reed. After 12 wk, no difference (P = 0.28) in herbicide tolerance was seen between the two haplotypes with respect to biomass. The 4.2-kg ae ha−1 rate of glyphosate and the 0.8- and 1.7 kg ai ha−1 rates of imazapyr reduced common reed by > 90% at 12 wk after treatment (WAT). Imazamox at 0.6 and 1.1 kg ai ha−1, and triclopyr at 3.4 and 6.7 kg ae ha−1 reduced common reed biomass (62–86%) at 12 WAT, though regrowth occurred. Diquat did not significantly reduce biomass by 12 wk. Glyphosate and imazapyr were the only herbicides that resulted in > 90% biomass reduction and corroborate control from previous studies.

As part of a census of the Indian rhinoceros Rhinoceros unicornis a survey was conducted to measure the extent of invasion by the neotropical plant mikania Mikania micrantha across major habitats of Chitwan National Park important for the conservation of the rhinoceros. Previous work has demonstrated that this fire-adapted plant can smother and kill native flora such as grasses and sapling trees, several of which are important fodder plants of the rhinoceros. Here, additional studies were conducted on the risks of anthropogenic factors (natural resource collection and grassland burning) contributing to the spread and growth of the plant. Mikania is currently found across 44% of habitats sampled and almost 15% of these have a high infestation (> 50% coverage). Highest densities were recorded from riverine forest, tall grass and wetland habitats and this is where the highest numbers of rhinoceroses were recorded in the habitats surveyed during the census. Local community dependence on natural resources in the core area of the Park is high. The range and volume of resources (e.g. fodder) collected and the distances travelled all pose a high risk of the spread of mikania. Of greater significance is the annual burning of the grasslands in the Park by local communities, estimated at 25–50% of the total area. It is imperative, therefore, that core elements of a management plan for mikania incorporate actions to control burning, reduce spread and raise awareness about best practice for local resource management by local communities.