Two factors that can degrade native plant community composition and structure, and hinder restoration efforts, are invasive species and chronic overbrowsing by ungulates such as white-tailed deer. Beginning in 2007, the effectiveness, costs, and impacts of Japanese barberry control treatments and herbivory on nonnative and native plant communities was examined at eight study areas over 4 to 5 yr. Prescribed burning and mechanical mowing by wood shredder or brush saw were utilized as initial treatments to reduce the aboveground portion of established barberry and were equally effective. Without a follow-up treatment, barberry had recovered to 56 to 81% of pretreatment levels 50 to 62 mo after initial treatment. Follow-up treatments in mid-summer to kill new sprouts included directed heating and foliar herbicide applications. Relative to untreated controls, follow-up treatments lowered barberry cover 50 to 62 mo after initial treatment by at least 72%. Although all follow-up treatments were equally effective, the labor cost of directed heating was four times higher than for herbicide applications. Follow-up treatment type (directed heating vs. herbicide) had minimal impact on species other than barberry. White-tailed deer herbivory had a larger impact on other species than did barberry control treatments. Native grass and fern cover was higher outside of exclosures. Areas inside exclosures had higher cover of Oriental bittersweet and multiflora rose, but not Japanese barberry. Thus, recovery of native communities will require more than simply removing the dominant invasive species where deer densities are high. Excellent reduction of Japanese barberry cover can be achieved using either directed heating or herbicides as follow-up treatments in a two-step process, but other invasive plants may become a problem when barberry is removed if deer populations are low.

Nomenclature: Glyphosate, triclopyr, 2,4-D, Japanese barberry, Berberis thunbergii DC. BEBTH, Oriental bittersweet Celastrus orbiculatus Thunb. CELOR, multiflora rose, Rosa multiflora Thunb. ex Murr. ROSMU.

Management Implications: Japanese barberry is an invasive shrub in the eastern United States and Canada that forms dense thickets that can inhibit forest regeneration and native herbaceous plant populations, and is associated with elevated populations of blacklegged ticks, which can be infected with the causal agent of Lyme disease, Borrelia burgdorferi. A reasonable objective of controlling an invasive species such as Japanese barberry, is not eradication of the invasive species per se, but the restoration of a community dominated by native herbaceous species and woody regeneration. This study found that a single treatment (e.g., mowing) is ineffective without a follow-up treatment. A variety of techniques using a two-step strategy can successfully control Japanese barberry for a period of at least 4 to 5 yr if there is an immediate follow-up treatment, albeit at a wide range of labor costs. Labor costs for follow-up treatments with a propane torch were at least four times higher than for herbicide applications, although both were equally effective at controlling barberry. However, invasive control by itself was insufficient to restore native communities in these areas with high white-tailed deer densities because deer herbivory had a larger impact on plant communities than control of Japanese barberry. Where deer densities are high, a successful restoration program must incorporate a program to reduce deer density to a level sufficient for native forbs to flower and set fruit and for tree seedlings to grow tall enough to be above browse heights—typically 2 m (6 ft). Successful restoration might also require introduction of locally extirpated species. A successful program should also include strategies to control those invasive species, such as Oriental bittersw

Extensive areas in the upper Midwest have been invaded by spotted knapweed, and effective management strategies are required to reestablish native plant communities. We examined effects of mowing, mowing plus clopyralid, or mowing plus glyphosate in factorial combination with hand pulling and burning on knapweed abundances on a knapweed-infested site in western Michigan. We applied mowing and herbicide treatments in summer 2008, and seeded all plots with native grasses and forbs in spring 2009. We conducted the knapweed pulling treatment from 2009 to 2012 in July. The prescribed burn was conducted in April 2012. By 2012, hand pulling reduced adult knapweed densities to 0.57 ± 0.12 m⁻² (0.053 ± 0.011 ft⁻²) (mean ± SE), which was 5.8% of nonpulled treatments, juvenile densities to 0.29 ± 0.07 m⁻² (2.1% of nonpulled treatments), and seedling densities to 0.07 ± 0.06 m⁻² (2.6% of nonpulled treatments). After 3 yr, hand pulling reduced seed bank densities to 68 ± 26 m⁻² as compared to 524 ± 254 m⁻² in nonpulled treatments and 369 ± 66 m⁻² in adjacent untreated areas of the study site. Without hand pulling, effects of mowing or mowing plus glyphosate were short-lived and allowed knapweed to rapidly resurge. In comparison, although a single mowing plus clopyralid treatment maintained significantly reduced densities of knapweed for 4 yr, by 2012 knapweed biomass in the nonpulled clopyralid treatment was approximately 60% of that in the other nonpulled treatments. Burning had minimal impacts on knapweed densities regardless of treatment combination, probably as a result of low fire intensity. Results demonstrated that persistent hand pulling used as a follow-up to single mowing or mowing plus herbicide treatments can be an effective practice for treating isolated spotted knapweed infestations or for removing small numbers of knapweed that survive herbicide applications.

Nomenclature: Clopyralid, glyphosate, spotted knapweed, Centaurea stoebe L.

Management Implications: We studied the interactive effects of mowing, herbicides, hand pulling, and burning on spotted knapweed control in western Michigan. Effects of a single mowing or mowing plus glyphosate on spotted knapweed were short-lived. In contrast, a single application of mowing plus clopyralid maintained reduced knapweed densities for 4 yr after treatment. In the fourth year, however, knapweed biomass in the nonpulled mowed plus clopyralid treatment was approximately 60% of the other nonpulled treatments, evidence that knapweed was resurging in the clopyralid treatment as well. Contrary to expectations, there were minimal effects of a single spring burn on spotted knapweed densities, probably as a result of suboptimal season of burn and cool burn-day temperatures, which caused low fire intensity. In comparison to other treatments, hand pulling more effectively controlled all knapweed life stages after 3 yr of treatment. Initially, hand-pulling removals were greatest on mowed-only plots (44 ± 7 m⁻², mean ± SE), increased in both clopyralid and glyphosate-treated plots in the second year as knapweed populations began to recover from herbicides, and then equalized at greatly reduced levels (0.6 ± 0.1 m⁻²) across all mowing and herbicide treatments by the fourth year. Removing knapweed by hand requires a large investment of time, however, and this must be taken into account when planning strategies for restoring knapweed-infested sites. To be effective, hand pulling needs to be applied persistently in advance of seed dispersal over several years. Hand pulling can be an effective practice for treating relatively small knapweed infestations in areas being restored to native vegetation, or as a follow-up treatment after herbicides have been used to reduce large infestations. Hand pulling also provides a tr

Yellow starthistle (Centaurea solstitialis) is among the most invasive plant species in the western United States. The long-term management of yellow starthistle should include an integrated approach that incorporates establishment of competitive vegetation. In this study, conducted in two locations at Fort Hunter Liggett in Monterey County, California, we evaluated the combination of prescribed burning, the herbicide aminopyralid, and reseeding of native broadleaf and grass species on both yellow starthistle control and native plant restoration. Both study sites were burned in late October 2009. Over the following season, aminopyralid was applied at three timings and native plant species were seeded at three timings, using both a drill-seeder and broadcast spreader. Evaluations over the next 3 yr showed that aminopyralid provided complete to nearly complete control of yellow starthistle when applied between January and March, and this level of control was maintained for two seasons. Native plants failed to establish when broadcast seeded, regardless of the timing. December and January drill seeding timings were the most successful in establishing native species. There was a strong herbicide and drill seed timing interaction effect on native grass cover at both study sites. Over the course of the study the native perennial grass Stipa cernua was the most successful seeded species to establish, but establishment was slow and required 3 yr. Our results indicate that a January or March aminopyralid treatment integrated with a native perennial grass drill seeding program in January offers the greatest probability of both successful yellow starthistle control and perennial grass establishment.

Nomenclature: Aminopyralid, yellow starthistle, Centaurea solstitialis L., Stipa cernua Stebbins & Love.

Management Implications: In previous studies we showed that a properly timed summer burn followed by application of the herbicide clopyralid in winter gave excellent control of yellow starthistle for two seasons. However, following management of a severe yellow starthistle infestation, resident vegetation often does not recover sufficiently to resist reinvasion, and it is often difficult to reseed native species in a Mediterranean climate characterized by seasonal rainfall and drought. In this study we evaluated the effect of prescribed burning followed by application of the similar herbicide aminopyralid at three timings (November, January, and March), crossed with drill or broadcast seeding of native species at three timings (December, January, and March). We assessed both yellow starthistle management and native plant restoration. Prescribed fire followed by January to March aminopyralid treatment gave 2 yr of near complete control of yellow starthistle. The November treatment did not provide season-long control of late-germinating starthistle. Broadcast seeding of native plants failed to establish any species. Of the three drill seed timings, only December and January resulted in successful establishment of just one native perennial grass species, even with above-average rainfall in the first 2 yr of the study. Neither a native annual grass nor several broadleaf species were able to establish or sustain their populations over time. Over the three seasons of the study, Stipa cernua established most successfully. There was a strong interaction effect for herbicide and drill seed timing, with January being the optimal timing for both herbicide application and perennial grass seeding. This timing not only offers the greatest probability of both successful yellow starthistle control and perennial grass establishment, but also can be used in a single-entry program that reduces costs by consolidating activities to one timing.

Prediction of invasive species distributions from survey data is widely recognized as a significant component of forest management and conservation planning. Leucaena leucocephala is the most aggressive invasive shrub and tree in the Hengchun peninsula in southern Taiwan. We analyzed geo-referenced data to identify potential variables of invasion and to predict likelihood of further invasion using boosted regression trees. Our results, which classified 92% of the cells correctly with regard to species presence and absence, indicated probability of invasion is correlated with climatic conditions (temperature and precipitation), landscape features (altitude; slope ratio and aspect; percentages of natural or secondary forest, agriculture land, developed area, and water bodies; and distances to the nearest forest edge and river), and anthropogenic factors (length of forest edge, and distances to the nearest road and agriculture land). The most influential variables are average annual temperature, altitude, precipitation, and slope. Continued range expansion by L. leucocephala is most likely to proceed (1) from the eastern and western portions toward the central portion of Hengchun township and (2) throughout the southern and toward the eastern portions of Manjhou township. Our model should provide useful information to aid forest managers in the development of long term monitoring and control strategies for L. leucocephala, in the early detection and eradication of newly established invasions, and also a framework for the integration and analysis of new presence and absence field data as they become available.

Nomenclature: White leadtree, white popinac, and jumbay, Leucaena leucocephala (Lam.) de Wit.

Management Implications: Leucaena leucocephala continues to expand its ranges in the southern Taiwan, and reliable prediction of habitats at risk is needed urgently. We drew upon extensive geo-referenced datasets to develop an invasion distribution model predicting possible range expansion of L. leucocephala in the Hengchun peninsula, Taiwan. Our analyses suggest that continued range expansion of L. leucocephala. However, the opportunity exists for reducing the likelihood of invasions via increased monitoring and early control efforts focused on low-elevation lands with low slope ratios that are close to roads, water, and/or forest edges. Areas surrounding agricultural and developed areas also should be targeted for prompt inspection and potential control measures. The complementarity between controlling and preventing plant invasions suggests that coordinated efforts to enhance ecosystem health would be more cost effective. More efforts should be directed toward educating residents in the Hengchun peninsula with the goal of engaging them in the prevention of L. leucocephala invasions and the restoration of infested areas. Our model should provide useful information to aid forest managers in the development of long term monitoring and control strategies for L. leucocephala, in the early detection and eradication of newly established invasions, and also in educational efforts directed toward residents in the Hengchun peninsula. Our model also provides a framework for the integration and analysis of new presence and absence field data as they become available.

Downy brome (Bromus tectorum) is an invasive, annual grass that has spread through much of the Great Basin desert but remains patchy at high elevation. This study evaluates control options for outlier infestations in the eastern Sierra Nevada, CA, based on their ecological effectiveness and their economic and practical feasibility. I tested the efficacy of hand-pulling, sheet-mulching, and soil solarization followed by broadcast and seedball seeding of native forbs and grasses. Downy brome cover, density, and dominance in the seed bank decreased with all removal treatments. Soil solarization and sheet mulching were most successful at eliminating downy brome (decreasing density by 99% after just 1 yr of treatment in both cases), but they had negative nontarget impacts on other herbaceous species. Germination of native seeds was low with both broadcast and seedball seeding, probably because of dry conditions. Each of the methods tested has potential for decreasing or eliminating small-scale, outlier infestations of downy brome along roadsides and in disturbed sites and thereby helping to contain the invasion.

Nomenclature: Downy brome, Bromus tectorum L.

Management Implications: Downy brome is an invasive, annual grass that has spread through much of the Great Basin desert, with significant effects on native species. Control of downy brome is particularly challenging because of its impacts to the fire cycle. At the high-elevation extent of its range, however, it remains patchy, and native plant communities are still relatively intact. Removal of these outlier infestations could reduce downy brome spread, prevent future impacts on the fire cycle, and help conserve native sagebrush–steppe habitat. I tested the ecological effectiveness and the economic and practical feasibility of several control options for downy brome infestations at the western edge of the Great Basin desert, including hand-pulling, sheet-mulching, and soil solarization, followed by broadcast and seedball seeding of native forbs and grasses. Hand-pulling led to significant reductions in downy brome cover, reduced its dominance in the seed bank, and increased forb cover. Downy brome was virtually eliminated after both soil solarization and sheet mulching, but these treatments had negative impacts on other herbaceous plants. Reseeding efforts were unsuccessful, likely because of low soil moisture availability. Based on my results, I would recommend hand-pulling for controlling downy brome in areas where the native seed bank remains relatively intact, such as along hiking trails adjacent to undisturbed plant communities. Soil solarization and sheet mulching would be better options for use along roadsides, pack stations, and in other disturbed areas. Each of these control methods is relatively low technology, safe, and, thus, appropriate for volunteer groups, which could decrease costs of implementation. Proactive investment in containment of downy brome invasion at range margins could have significant economic and ecological benefits into the future.

Because of economic and environmental constraints, alternatives to chemical management of Canada thistle (Cirsium arvense) are frequently sought, but adequate nonchemical suppression of this invasive species remains elusive. Combining biological control with other tactics may be an effective approach to suppress Canada thistle, but more information is needed about how environmental conditions affect interspecific interactions. We investigated effects of a biocontrol agent (Hadroplontus litura, a stem-mining weevil) and a potential plant competitor (common sunflower, Helianthus annuus, native annual) on Canada thistle under two soil nutrient regimes in outdoor microcosms. Larval mining damage was relatively light, and weevils negatively impacted only main shoot height and flower number. All measures of Canada thistle performance were reduced when plants were grown with common sunflower or in reduced nutrients, although effects of the latter on root biomass were not significant. Effects of common sunflower and soil nutrients on Canada thistle were generally additive, though a marginally insignificant interaction indicated a trend for greatest flower number with high nutrients and absence of common sunflower. Effects of weevils and common sunflower on Canada thistle were also additive rather than interactive. Although larval damage ratings were significantly greater on plants grown in high-nutrient soil, under our experimental conditions weevils and soil nutrients did not have a significant interactive effect on Canada thistle plants. Our results indicate that H. litura is a relatively weak biological control agent, but when combined with competitive desirable vegetation, some level of Canada thistle suppression may be possible, especially if soil nutrient levels are not highly enriched from agricultural runoff. Assessing the true ecological impacts of Canada thistle infestations may be an important direction for future research.

Nomenclature: Stem-mining weevil, Hadroplontus litura Fabricius, Canada thistle, Cirsium arvense (L.) Scop., common sunflower, Helianthus annuus L.

Management Implications: Canada thistle is a problematic invasive plant in many temperate regions of the northern hemisphere, and management continues to be a challenge. Research suggests that integrating multiple control tactics enhances suppression of Canada thistle, but that effects often depend on environmental context. In our microcosm study, weevil herbivory, common sunflower competition, and reduced levels of soil nutrients had substantial negative effects on many measures of Canada thistle growth and reproductive capacity. Overall, the latter two factors exerted the strongest negative effects; however, weevil damage was generally light. Canada thistle grown in high-nutrient soils had greater main-stem biomass, numbers of side shoots, and numbers of flowers, even though larval stem-mining damage was greater for these plants. Common sunflower proved to be a good competitor against Canada thistle, and sowing this type of fast-growing annual forb, which occupies a similar soil niche to Canada thistle, alongside perennial native plants (e.g., competitive grasses) may enhance restoration outcomes.

Successful management of downy brome (also known as cheatgrass) requires understanding land managers' perceptions and decisions about whether to invest in its control. We investigated ranchers' and natural resource professionals' (NRPs) perceptions and knowledge about downy brome ecology and its impacts, their current downy brome management practices and satisfaction with those practices, and their information and technical needs using focus groups and a mail survey of ranchers and NRPs in Colorado and Wyoming. Both groups thought downy brome was a problem, and perception of the severity of downy brome corresponded to the level of infestation in the respondent's region. NRPs identified downy brome as a bigger problem than did ranchers from the same area in all but one region. Ranchers were most likely to use early spring grazing to control downy brome, and NRPs were most likely to use seeding, imazapic herbicide, or a combination of methods. Both groups reported that the primary constraint to controlling downy brome was that other weeds were a higher priority. Ranchers and NRPs wanted more information about the control methods they were already likely to use as well as other downy brome control methods. Our findings suggest that (1) listing a species as a noxious weed may provide an important incentive to control it, but trade-offs among control efforts for different species must be carefully considered; (2) managers need to know more about low-cost, low-labor strategies for managing downy brome; and (3) some managers need to be informed about how to identify downy brome, its potential negative effects, and how to prevent its spread. Better quantification of the economic and ecological impacts of downy brome in the Central Rocky Mountains, continued development of effective and economically viable management methods, and improvement in the dissemination of that information to land managers are necessary for successful control of downy brome.

Nomenclature: Imazapic, downy brome, Bromus tectorum L. BROTE.

Management Implications: Where downy brome is common, ranchers and natural resource professionals (NRPs) were likely to know and be concerned about it. However, other weeds, especially those officially designated as noxious weeds, may be a higher priority for control, and that could limit land manager motivation and resources available to manage downy brome. NRPs were usually more concerned about downy brome than ranchers, which may reflect the value downy brome has as early season livestock forage. Land managers favored using control methods that were readily available to them. Ranchers preferred using grazing as a tool for controlling downy brome, whereas NRPs preferred using herbicides and combining multiple methods in their approaches. Both groups reported using and being satisfied with seeding. Constraints to managing downy brome included the need to allocate scarce financial resources to control of higher priority species and labor limitations. Although ranchers and NRPs wanted information about how to use their preferred management methods most effectively, both manager groups wanted to learn about different control options and effective use of livestock grazing for control. Our study highlights several important considerations when working to improve education and coordinated management of downy brome. (1) Cost is a major constraint to control of downy brome. When land managers evaluate the trade-offs in allocating control efforts for different species, listing of a species as a noxious weed influences that calculation. (2) In designing a downy brome management plan, it is important to consider the compatibility of proposed control methods with a land manager's existing operation, management tools, and labor availability and to recognize potentially differing perceptions of effective management approaches between ranchers and NRPs. (3

Cogongrass [Imperata cylindrica (L.) Beauv.] is a warm-season, rhizomatous grass native to southeast Asia that has invaded thousands of hectares in the southeastern United States. Its negative impacts on pine forests have been well documented, and aggressive control is widely recommended. Although repeated herbicide treatments are effective for suppression, integrated strategies of prescribed burning coupled with herbicide treatment and revegetation are lacking in pine systems. In particular, longleaf pine forests, which are typically open, fire-dependent, communities, are highly susceptible to cogongrass, which is a pyrogenic species. To address management goals for cogongrass control and herbaceous restoration in longleaf pine forests better, field studies were conducted in southwestern Alabama from 2010 to 2012. Two longleaf pine forests with near-monotypic stands of cogongrass in the understory were selected for study. Treatments included combinations of winter prescribed fire, spring and fall glyphosate herbicide treatments, and seeding a mix of native, herbaceous species. Data were collected for three growing seasons following study initiation, and included seasonal herbaceous species cover and final cogongrass shoot and rhizome biomass. Species richness and diversity were calculated and analyzed to ascertain treatment effects over the duration of the study. Burning slightly improved cogongrass control with glyphosate, but had no effect on total cover, species richness, or species diversity. Three glyphosate treatments reduced total vegetative cover and nearly eliminated cogongrass cover, shoot, and rhizome biomass. Glyphosate and glyphosate seeding also increased herbaceous species richness and diversity. However, aboveground productivity in treated plots was significantly lower than productivity in the untreated control, which was almost exclusively cogongrass. These studies indicate that glyphosate and integrated strategies utilizing glyphosate and seeding are very useful for cogongrass management and increasing herbaceous species richness and diversity in longleaf pine.

Nomenclature: Glyphosate, cogongrass, Imperata cylindrica (L.) Beauv., longleaf pine, Pinus palustris Mill.

Management Implications: Cogongrass is a serious threat to southeastern pine ecosystems. Although numerous control studies have been conducted, information is still lacking for cogongrass management in longleaf pine. With longleaf pine, many land managers want to recreate mixed pine/open savannah conditions with a species-rich herbaceous understory. However, cogongrass is a significant obstacle to that goal, as it forms near-monotypic stands beneath longleaf pine that are of little value. To address this problem, we tested multiple integrated methods, including prescribed burning, glyphosate treatment, and seeding native herbaceous species. We found that glyphosate treatment following prescribed burning provided a minor but significant increase in cogongrass control compared to glyphosate-treated, unburned plots. However, the effect was short-lived and not useful when follow-up glyphosate treatments were applied. Glyphosate treatment combined with seeding native species generally increased cover, species richness, and diversity compared to glyphosate treatment alone. Burning and seeding without glyphosate treatment was ineffective, as cogongrass quickly recovered. In summary, we found that glyphosate treatment was critical for cogongrass control and improvements in native species richness and diversity.

When exotic species invade a region, it becomes important to assess their invasiveness in adjacent uninvaded regions to determine if weed prevention measures are needed. Leafy spurge and knapweed species are absent from the vast majority of eastern Montana, but the region is surrounded by regions heavily invaded by these species. To assess invasiveness of leafy spurge and Russian and spotted knapweed in common eastern Montana grassland sites, I introduced these species to three sites as seeds (120 live seeds plot⁻¹) and seedlings (6 plot⁻¹). I assessed how common grazing regimes influenced invasiveness by imposing cattle, sheep, mixed grazing (i.e., cattle plus sheep), and grazing exclusion treatments for 7 yr. Invader survival did not appear to differ greatly among sheep, cattle, and mixed grazing treatments, but excluding grazing lowered probabilities that plots maintained invaders for the entire study period at two of three sites. At these same sites, grazing exclusion increased growth rates of those invaders that did survive, at least in the case of leafy spurge. Regardless of grazing treatment or site, however, large proportions of plots did not maintain invaders through the end of the study period. At one heavy clay site, only one small leafy spurge plant persisted through the end of the study. In the seventh study year, the plots with the most leafy spurge and Russian knapweed produced 222 and 112 stems, respectively, and the stems remained mostly confined to the 2- by 2-m plots. These findings suggest that, barring intense disturbance, leafy spurge and spotted and Russian knapweed might be incapable of invading some grasslands of eastern Montana, particularly upland sites with high clay content. Any upland sites in the region these species are capable of invading will likely be invaded only very slowly.

Nomenclature: Leafy spurge, Euphorbia esula L., Russian knapweed, Acroptilon repens (L.) DC., Spotted knapweed, Centaurea stoebe L.

Management Implications: Important management decisions hinge on how capable invasive plants are of spreading from invaded to uninvaded regions. I evaluated the invasiveness of leafy spurge and spotted and Russian knapweed in eastern Montana, a largely weed-free region surrounded by regions supporting large infestations of these invaders. Despite being introduced from large numbers of seeds and seedlings, the invaders failed to survive the 6-yr study period at one of three study sites, suggesting that the species cannot invade the many areas of eastern Montana that resemble that study site, particularly upland sites with high clay content. Extinction rates were high at the other two sites as well, but invaders did persist and grow modestly in some plots at these sites. Six yr after introduction, all invaders remained mostly confined to the 2- by 2-m plots where they were planted. This suggests that any invasions by the focal species in eastern Montana will likely proceed slowly, and careful scouting of any given uninvaded area once every several years should be sufficient to detect and efficiently eradicate newly colonizing populations. Finally, the study had grazing exclusion, sheep, cattle, and mixed grazing (cattle plus sheep) treatments. Compared to the grazing treatments, grazing exclusion decreased the number of plots that maintained invaders for the entire study period. Conversely, grazing exclusion increased invader biomass production in those plots that did maintain invaders for the entire study period, at least in the case of leafy spurge. Collectively, these results suggest grazing exclusion alone is unlikely to prevent invasions indefinitely. These results are consistent with research showing sheep grazing can be used to constrain spotted knapweed and leafy spurge abundances.

Downy brome is a problematic invasive annual grass throughout western rangeland and has been increasing its abundance, spread, and impacts across Montana during the past several years. In an effort to develop effective management recommendations for control of downy brome on Montana rangeland, we compiled data from 24 trials across the state that investigated efficacy of imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC) applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We ran a mixed-model ANOVA to test for main effects and interactions across application rate (70, 105, 141, 176, and 211 g ai ha⁻¹), application timing (preemergent [PRE], early postemergent [EPOST, one- to two-leaf growth stage], and postemergent [POST, three- to four-leaf growth stage]), and adjuvant (MSO, NIS). Application timing and rate interacted to affect downy brome control (P  =  0.0033). PRE imazapic application resulted in the lowest downy brome control (5 to 19%), followed by POST application (25 to 77%) and EPOST application (70 to 95%). Downy brome control remained fairly consistent across rates within application timing. Adjuvant (MSO or NIS) did not affect downy brome control (P  =  0.2789). Our data indicate that POST application at 105 to 141 g ai ha⁻¹ provides the most-consistent, short-term control of downy brome. Furthermore, applying imazapic to downy brome seedlings shortly after emergence (one- to two-leaf growth stage) provided better control than applying it to older downy brome seedlings (three- to four-leaf growth stage).

Nomenclature: Imazapic; downy brome, Bromus tectorum L. BROTE.

Management Implications: Management of the invasive annual grass downy brome (Bromus tectorum) remains challenging on western rangeland. Chemical control has produced inconsistent results, especially with the herbicide imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC). Downy brome has been increasing during the past several years on rangeland across Montana where effective management recommendations for chemical control are needed. We compiled data from 24 independent herbicide trials across Montana, from 2000 to 2010, which investigated the efficacy of imazapic applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We tested for general trends in downy brome control across application rate (70, 105, 141, 176, 211 g ai ha⁻¹ [1, 1.5, 2, 2.5, and 3.1 oz ai ac⁻¹]), application timing (preemergent [PRE], early postemergent [EPOST, one- to two-leaf growth stage], and postemergent [POST, three- to four-leaf growth stage]), and adjuvant (MSO, NIS). Downy brome control was especially affected by application timing. PRE imazapic application resulted in the lowest downy brome control (5 to 19%), followed by POST application (25 to 77%) and EPOST application (70 to 95%). Downy brome control remained fairly consistent across rates within application timing. Adjuvant did not affect downy brome control. Our data indicated that an EPOST (downy brome at the one- to two-leaf growth stage) application at 105 to 141 g ai ha⁻¹ provided the most-consistent control of downy brome. Most published literature on the efficacy of imazapic for controlling downy brome do not report growth stage at the time of application, but our data indicate that timing of imazapic application influences its efficacy. Therefore, land managers should be aware of the growth stage of downy brome when imazapic applications are made and interpret outcomes with this factor in mind.

Developing management strategies for invasive plant species requires identifying effective treatment methods (e.g., physical or chemical treatments) and optimally timing their application. For invasive annual plants, effects of treatments on seed production and germinability are paramount to reduce seed banks and subsequent plant establishment. We compared effects of a range of physical and chemical treatments applied to plants containing seeds at different developmental stages at field sites in the Mojave Desert (Nevada and Arizona) for managing the exotic annual forb, African mustard. Effectiveness of physical treatments (hand pulling entire plants, breaking plants, or separating siliques from plants) for reducing African mustard seed size and germination varied by treatment and seed maturity stage at which treatments were applied. With all treated plant material remaining in the field (i.e., not bagged and transported off site), hand pulling or breaking plants resulted in 90 to 100% of developing and developed seeds still able to germinate. Separating siliques from plants, however, resulted in 0% germination of undeveloped and developing seeds. All three tested herbicides (glyphosate, 2,4-D, and metsulfuron) reduced germination to zero or near zero across all seed development stages. Results suggest that physical treatments are most effective at early stages of seed development, whereas several different herbicides are effective across seed developmental stages. Results also highlight the importance of considering the potential for continued seed development and germinability on treated plant material when choosing invasive plant treatment types and timing.

Nomenclature: African mustard, Brassica tournefortii Gouan.

Management Implications: Introduced to North America (California) by 1927, the annual African mustard is a priority invasive forb for management in southwestern North American arid lands such as the Mojave Desert. A field experiment in Lake Mead National Recreation Area in the eastern Mojave Desert revealed that three different physical treatments (hand pulling entire plants, breaking plants off at the base, or separating siliques from plants) differed in their ability to reduce African mustard seed germination across three seed development stages (ranging from undeveloped to fully developed seeds). Once seeds had fully developed, no physical treatment reduced seed germination below 50%, and at least 20% even of undeveloped seeds continued to develop and were germinable on pulled and broken plant material left in the field. Thus, the window for applying physical treatments is largely restricted to before any seed development. Otherwise, treated plant material needs to be sterilized or transported off site to avoid continued development and germination of seed even after plants are treated. A second field experiment revealed that three different herbicides (glyphosate, 2,4-D, and metsulfuron) eliminated or nearly eliminated germination across all three seed development stages. Results suggest that managers have several herbicide options effective at preventing germination even when applied late in plant development to fully developed seeds. Results highlight the importance of considering germination potential of residual seeds on treated plant material when evaluating treatments.

Predicting site vulnerability to nonnative plant establishment remains a difficult goal. Seedling survival is an important component of population dynamics and can affect the success of control strategies. Field manipulations allow potential causal mechanisms of site vulnerability to be evaluated under realistic environmental conditions. We conducted field studies to determine the effects of plant competition and differing precipitation regimes on spotted knapweed seedling survival. We also examined the effect of herbivory on rosette survival and growth. Seeds were sown into plots with vegetation intact or removed at three sites. Seeds were also sown into plots where plant competition and precipitation were manipulated in a factorial design at a single site. Field studies demonstrated that site accounted for much of the variation in emergence rate, while herbivory and plant competition affected seedling survival rates. We observed a wide range in emergence rates, with site averages ranging from 13.1 to 42.5%. Survival the following year ranged from 0.5 to 9.4% of sown seeds. Rosette survival was significantly higher when herbivores were excluded from plots. Below average precipitation reduced seedling survival; however, even with supplemental water, dry-down of exposed sites resulted in low seedling survival. Of the 8,000 seeds added to plots in one study, by autumn, only eight plants resulted, seven of which survived in watered plots with intact vegetation. Collectively, these results show that seedling survival is a critical phase in spotted knapweed population dynamics and can vary among habitats on the basis of plant competition and precipitation. Furthermore, herbivory affects all stages of the lifecycle from the seedling onward. The observed differences help explain the reported variability in seedling survival in the literature and inform efforts to control spotted knapweed using plant competition and biological controls.

Nomenclature: Spotted knapweed, Centaurea stoebe L. ssp. micranthos (Gugler) Hayek.

Management Implications: Spotted knapweed is an invasive, perennial rangeland plant in North America. It is mostly unpalatable to livestock and has the potential to produce thousands of seeds yearly from dense monocultures that limit local plant diversity. Various biological control agents have been introduced to control this plant. They reduce plant reproduction both directly through seed predation and indirectly through reducing flower production and plant life span. This study was conducted in a spotted knapweed infestation on the Front Range of Colorado near Boulder, CO. We examined how established vegetation and herbivory affected the fate of the seeds that are produced. We added spotted knapweed seeds to field plots where vegetation and precipitation levels were manipulated. We also monitored plots in established spotted knapweed patches to examine the effect of herbivory on small rosettes. Spotted knapweed seedling survival was lower when plant competition was present but varied substantially among the sites. The effect of plant competition on seedling survival was subject to a moisture gradient; the presence of non-knapweed plants had a positive effect on seedling survival when precipitation levels were high. Herbivory negatively affected both seedling and rosette survival. The presence of established vegetation and insect herbivory decrease spotted knapweed survival, and biological control may be sufficient to control spotted knapweed at sites that have a high insect populations and low seedling emergence and survival.

The presence of landscape disturbances increases the establishment of exotic plants inside natural areas. Here, we examine the effect of human disturbances to prairie landscapes on the distribution and abundance of Kentucky bluegrass and smooth brome, exotic grasses that threaten the integrity of prairie ecosystems throughout the northern Great Plains. Using plant inventory data from Riding Mountain National Park in Manitoba, Canada, we investigated how roads, trails, and the intensity of historic livestock grazing affect the distribution and abundance of exotic grasses. On the basis of our results, both Kentucky bluegrass and smooth brome were more abundant in areas closer to roads. Kentucky bluegrass was also more abundant in areas farther from trails and those historically grazed by cattle. Our research demonstrates that the effect of landscape disturbances on exotic grasses varies between species and suggests that patterns of invasion may reflect different introduction histories. Given our findings, conserving the integrity of northern fescue prairies should account for human disturbances of landscapes and their effects on the proliferation of exotic plants into areas of native prairie.

Nomenclature: Smooth brome, Bromus inermis Leyss. BROIN, Kentucky bluegrass, Poa pratensis L. POAPR.

Management Implications: Our research demonstrates that human disturbance of prairie landscapes, including roads, trails, and historic livestock grazing, affect the distribution and abundance of Kentucky bluegrass and smooth brome in northern fescue prairies. Conservation managers concerned about the proliferation of these invaders throughout the Great Plains can use distances from roads and grazing history to prioritize their inventory and management. For example, by focusing their attention on road margins, managers may be able to reduce the proliferation of Kentucky bluegrass and smooth brome into adjacent areas of native prairie. Our work also illustrates the persistent effect of historic livestock grazing on the abundance of Kentucky bluegrass and suggests that managers could reduce its proliferation by focusing on source areas located within historic grazing disturbances. Future management of northern fescue prairies will require limiting or restoring human disturbances of prairie landscapes in areas where the conservation of native biodiversity is a management priority.

The common reed (Phragmites australis) is one of the most invasive vascular plants in northeastern North America. A competitive genotype from Eurasia has recently invaded road and agricultural ditches, which facilitate the dispersal of the plant over long distances. However, large tracts of roadsides—apparently propitious for the establishment of the plant—are not invaded by the grass. We hypothesized that the absence of the invader is associated with physical and biological characteristics of roadsides. To test this hypothesis, we collected field data and developed two statistical models to explain the presence or absence of the common reed along a highway of southern Quebec highly invaded by the plant but with contrasting patterns of common reed distribution. The models explained 23 to 30% of the total variance and correctly predicted the presence or absence of common reed 71% of the time. The models suggest that a dense woody plant cover over a drainage ditch limits the establishment and/or expansion of the common reed, probably by competition for light and space. Also, shaded ditches are not subjected to a frequent maintenance, and are therefore less disturbed, probably further reducing common reed invasion because the germination of their seeds is less likely without soil disturbance. This study yields insights on the potential of woody plants for controlling the expansion of invasive grasses, and could help to justify the preservation of dense shrubs and tree hedges along right-of-ways.

Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud.

Management Implications: The common reed (Phragmites australis) is one of the most invasive vascular plants in northeastern North America. A competitive genotype from Eurasia has recently invaded road and agricultural ditches, which facilitate the dispersal of the plant over long distances. However, large tracts of roadsides—apparently propitious for the establishment of the plant—are not invaded by the grass. We suggest here that a dense woody plant cover over a drainage ditch is likely to prevent the establishment or the subsequent expansion of the common reed. In jurisdictions where the use of herbicides is prohibited for controlling the common reed, preserving well-established shrub or tree hedges over roadside ditches could be an efficient low-cost alternative to prevent common reed invasions. Planting shrub hedges in drainage ditches could also be a measure to prevent the establishment or survival of common reed seedlings along newly created highways, especially where the roads cross wetlands highly susceptible to be invaded.