The distribution of genetic diversity in invasive plant populations can have important management implications. Alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] was introduced into the United States around 1900 and has since spread throughout much of the southern United States and California. A successful biological control program was initiated in the late 1960s that reduced A. philoxeroides in the southern United States, although control has varied geographically. The degree to which variation among genotypes may be responsible for variation in control efficacy has not been well studied due to a lack of genetic data. We sampled 373 plants from 90 sites across the United States and genotyped all samples at three chloroplast regions to help inform future management efforts. Consistent with clonal spread, there was high differentiation between sites, yet we found six haplotypes and high haplotype diversity (mean h = 0.48) across states, suggesting this plant has been introduced multiple times. Two of the haplotypes correspond to previously described biotypes that differ in their susceptibility to herbicides and herbivory. The geographic distribution of the three common haplotypes varied by latitude and longitude, while the other haplotypes were widespread or localized to one or a few sites. All the haplotypes we screened are hexaploid (6n = 102), which may enhance biological control. Future studies can use these genetic data to determine whether genotypes differ in their invasiveness or respond differently to control measures. Some states, for instance, have mainly a single haplotype that may respond more uniformly to a single control strategy, whereas other states may require a variety of control strategies. These data will also provide the basis for identifying the source regions in South America, which may lead to the discovery of new biological control agents more closely matched to particular genotypes.

Ventenata [Ventenata dubia (Leers) Coss.], an invasive winter annual grass, negatively impacts grassland community composition and function in the Pacific Northwest. Ventenata dubia established in Palouse prairie (PP) and canyon grasslands (CG) of northern Idaho/eastern Washington in the mid-1980s to early 1990s. Understanding and comparing patterns of invasion can elucidate future trends as its range expands. We performed surveys in PP (2012 and 2013) and CG (2018) to assess V. dubia abundance. Specifically, we correlated species richness, Shannon diversity, rank abundance, and indicator species with no, low (<12.5%), and high (>12.5%) V. dubia cover. We used nonmetric multidimensional scaling analysis (NMDS) to visualize species similarities and associations with abiotic variables. In both ecoregions, V. dubia was very common, appearing in nearly 60% of 450 plots. When present, V. dubia cover averaged 26% (±2.3 SE) in PP and 19% (±1.8 SE) in CG. Indigenous plant species richness and diversity were lowest in plots with high V. dubia cover. In CG, this relationship held for nonindigenous species; in PP, nonindigenous plant richness and diversity were higher with high V. dubia cover. Ventenata dubia and other winter annual grasses (Bromus spp., medusahead [Taeniatherum caput-medusae (L.) Nevski]) were moderately associated according to the NMDS analysis. Indicator species analysis showed V. dubia was positively associated with nonindigenous winter annual grasses and negatively associated with indigenous low shrub species. Abiotic factors that explained V. dubia abundance included shallow soils and a south to west aspect. Overall, these findings indicate V. dubia can successfully invade both dry and relatively wet plant communities and is more abundant than other invasive annual grasses. We suggest these findings foreshadow what will happen in sagebrush steppe and Great Plains grasslands, regions where V. dubia recently became established.

Callery pear (Pyrus calleryana Decne.), a native of eastern Asia, has recently emerged as an important woody invader in much of the eastern United States. Little is known about its ecology in its new range. Its shade tolerance may be an important indicator of areas it is likely to invade. In this study, allometric equations were first developed to predict aboveground biomass components, including wood, branches, bark, leaves, and fruit, from diameter at stump height (dsh; 25 cm), by destructively harvesting 13 trees, ranging from 0.1 to 19.3 cm dsh. Then, a total of 23 wild-grown stands in the northern Kentucky/southwestern Ohio region were surveyed, with diameters of all woody stems sampled. Pyrus calleryana density, basal area, aboveground biomass, stand density index, size distribution inequality, and importance value were calculated for each site. Two-factor Weibull distributions were fit to diameter distributions. Allometric equations provided good fits for total aboveground biomass as well as individual components. Aboveground biomass levels fell below mean levels of native forest stands found in the United States. Stand density indices yielded values typical of shade-intolerant or midtolerant species. Stands with smaller trees generally had steeply declining monotonic diameter distributions, while stands with larger trees trended toward positively skewed monotonic distributions. These findings are consistent with a species that is either shade-intolerant or midtolerant. Thus, while this species is expected to invade open or disturbed areas, it is not expected to be an important invader under forest canopies. However, its extended deciduous habit is one shared by other understory woody invaders, and so this may allow it to survive under forest canopies.

Genetic assays to identify herbicide-resistant plants are a promising tool to reduce herbicide failures. However, the genetic basis of herbicide resistance is frequently unknown. In clonal weed species, DNA fingerprinting could be a useful tool to identify known resistant versus susceptible genets (clones) that occur in multiple locations, without an immediate need for understanding the genetic mutation(s) conferring resistance. Eurasian watermilfoil (Myriophyllum spicatum L.) and hybrids with native northern watermilfoil (Myriophyllum spicatum × Myriophyllum sibiricum Kom.) are mostly clonal invasive aquatic plants, and the same clones can be found in multiple waterbodies. Previously, a clone was confirmed as resistant to the commonly used herbicide fluridone, and a recent genetic survey in Michigan identified this genotype (MG-237) in at least seven other lakes. We hypothesized that MG-237 collected from different lakes would also exhibit fluridone resistance. However, MG-237 may have accumulated resistance mutations at different times during its spread across Michigan, resulting in fluridone-resistant and fluridone-susceptible MG-237 clones distributed in different lakes. We used a herbicide assay to test the response of several accessions, including MG-237 accessions from multiple lakes, to the Michigan operational rate of 6 µg L−1 fluridone. We found that all accessions of MG-237 exhibited resistance to 6 µg L−1 fluridone. A second genotype (MG-377) was also resistant to 6 µg L−1 fluridone. The rest of the accessions were found to be significantly injured by 6 µg L−1 fluridone. Our results suggest that 6 µg L−1 fluridone would not effectively control waterbodies dominated by MG-237 or MG-377, whereas waterbodies dominated by the other genotypes in our study would likely be controlled. Although more studies are needed to identify the variation in sensitivity of the accessions tested here and the genetic basis of fluridone resistance in Myriophyllum, our results suggest that multilocus genotype data may be an effective tool to identify and track herbicide-resistant genotypes of Myriophyllum in the short term.

Callery pear (Pyrus calleryana Decne.) is rapidly spreading in the United States, gaining attention in the last two decades as a serious invasive pest. Recommended control methods include foliar, basal bark, cut stump, and hack-and-squirt application of herbicides, but there are few published studies with replicated data on efficacy. Four readily available herbicidal active ingredients and a combination of two active ingredients were tested for control efficacy against P. calleryana in old-field areas and loblolly pine (Pinus taeda L.) understory. Basal bark applications (triclopyr, triclopyr + aminopyralid), foliar applications (glyphosate, imazapyr), and a soil application (hexazinone) effectively killed P. calleryana with the exception of hexazinone at one site, where rainfall may not have been optimal. Foliar application of glyphosate provided the most consistent control. Our results demonstrate efficacy of registered herbicide formulations for P. calleryana control in two geographic locations and two habitat types. The need for development of integrated pest management programs for P. calleryana is discussed.

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 invasion of Lehmann lovegrass (Eragrostis lehmanniana Nees) in rangelands of Chihuahua, Mexico, has resulted in a need for revegetation to recover lost forage productivity. Thus, new knowledge on generating alternatives to improve these invaded grasslands is of great importance. This study evaluated seedbeds prepared with unconventional tillage implements and seeded with a grass mixture to reduce the plant density of E. lehmanniana while increasing the productivity of an invaded semiarid grassland of Chihuahua. The unconventional tillage implements were: a Rangeland Harrow, which was used to prepare the Striped Harrowing and Full Harrowing seedbeds; Rangeland Rehabilitator, which was used to prepare the Deep-Stingray Subsoiler seedbed; and a Tandem-type Aerator Roller, which was used to prepare the Double-Digging Aeration seedbed. An area without tillage was left as a control. The seed mixture was composed of blue grama [Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths var. Hachita] (25%); sideoats grama [Bouteloua curtipendula (Michx.) Torr. ‘6107 Kansas’] (25%); green sprangletop [Leptochloa dubia (Kunth) Nees var. Van Horn] (5%); weeping lovegrass [Eragrostis curvula (Schrad.) Nees var. Ermelo] (40%), and Columbus grass [Sorghum almum Parodi] (5%). The experiment was conducted across 4 yr, and the evaluation started at the second year. Plant density and dry matter (DM) production were evaluated per species. In the control plot, the plant density of E. lehmanniana increased approximately 180% from the 2nd to the 4th year (18 to 50 plants m−2). The use of unconventional tillage implements for seedbed preparation and the inclusion of E. curvula in the seed mixture decreased E. lehmanniana density in more than 50% of plots and increased DM production in around 100% of plots. Considering the whole experimental period, in all the prepared seedbed treatments, E. curvula had the highest establishment and DM production of all the seeded species. The native species B. gracilis, B. curtipendula, and L. dubia had poor establishment in all the prepared seedbeds.

In this case study, we used point mapping data to evaluate long-term treatment of invasive tree-of-heaven [Ailanthus altissima (Mill.) Swingle]. This study at the Buffalo National River included 21 project areas ranging in size from 0.02 to 11.3 ha and spanned 5 to 8 yr depending on the site. The control techniques varied depending on the year and included the application of herbicide, which also varied over the course of the study and included imazapyr, triclopyr, and triclopyr+fluroxypyr. Treatments during the first year reduced local A. altissima populations by an average of 66%. Long-term repeated treatments led to decreases of at least 90% in 70% of the project areas and at least 73% in 95% of the project areas. Only one project area was found to support no plants during the final treatment year. Ailanthus altissima increased at most project areas during an unusually wet year and was more likely to increase than decrease in intervals >1 yr with no treatment. Over the temporal and spatial scales of this case study, we observed high levels of control that will likely meet the specified levels and ecological benefits required in many similar efforts. Land managers must, however, make a long-term commitment of resources to achieve lasting control of this invasive species.

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.

Estimates of plant biomass are helpful for many applications in invasive plant science and management, but measuring biomass can be time-consuming, costly, or impractical if destructive sampling is inappropriate. The objective of this study was to assess feasibility of developing regression equations using a fast, nondestructive measure (cover) to estimate aboveground biomass for red brome (Bromus rubens L.), a widespread nonnative annual grass in the Mojave Desert, USA. At three study sites, including one measured for three consecutive years, B. rubens cover spanned 0.1% to 85% and aboveground biomass 1 to 321 g m−2. In log10-transformed linear regressions, B. rubens cover accounted for 68% to 96% of the variance in B. rubens biomass among sites, with all coefficients of determination significant at P < 0.05. For every doubling of percent cover, biomass was predicted to increase by 78%, 83%, and 144% among the three sites. At the site measured for three consecutive years, which ranged in rainfall from 65% to 159% of the long-term average, regression slopes each year differed from other years. Regression results among sites were insensitive to using cover classes (10 classes encompassing 0% to 100% cover) compared with simulated random distribution of integer cover within classes. Biomass of B. rubens was amenable to estimation in the field using cover, and such estimates may have applications for modeling invasive annual plant fuel loads and ecosystem carbon storage.