Invasive Weed Management Research Articles

Talking Big: Lessons Learned from a 9000 Hectare Restoration in the Northern Tallgrass Prairie

Large tracts (>1000 ha) of prairie are essential to the sustainability of grassland ecosystem services, yet in many ecoregions only small fragments remain. Glacial Ridge is among the largest prairie-wetland restorations ever attempted. Started in 2000, the 9000 ha project in northwest Minnesota, USA, was initiated to reconnect 14 small tallgrass prairie remnants. In all, 15,200 ha of contiguous habitat comprise the project's direct accomplishment. We created a partnership of more than 30 organizations, filled 177 km of drainage ditch, restored 1240 ha of wetland, and replanted 8100 ha. Flooding has been mitigated, water quality improved, and native vegetation reestablished. Animals not documented for decades have again occupied the site. Despite these accomplishments, the project would have been unnecessary if the land had been purchased in the 1970s, prior to conversion to agriculture, at one-tenth the restoration cost. Our challenges related to funding, differences in partners' restoration philosophy, community concerns about floods and tax losses, difficulties in obtaining seed, and follow-up management of invasive weeds. We summarize the restoration process and share basic principles that will help others to develop large-scale prairie restoration projects in the future.

Building Capacity to Manage Noxious and Invasive Weeds in the Southwestern United States

P rior to the 1990s, awareness and concern regarding the negative economic and ecological impacts of invasive weeds i on rangelands in the southwestern United States (the Southwest) was notably lacking. While invasive weed education and management activities were proactively being carried out in many parts of the United States during that time, only a few land management agencies in the Southwest were actively managing invasive weed populations and conducting public awareness cam- paigns. The need to heighten public awareness regarding invasive weeds in the Southwest was thought to be critical because the weed-infested areas in this region were considered to be relatively small and manageable compared to other regions of the United States. DOI: 10.2458/azu_rangelands_v34i2_m asayesva

Inderjit (ed.): Management of Invasive Weeds

Author(s): Parker, Ingrid M.; Holloran, Pete; Swope, Sarah M.; Cummings, Justin; Grove, Sara; Fresquez, Carla

The Politics of Invasive Weed Management: Gender, Race, and Risk Perception in Rural California*

Abstract “Biological invasions” are now recognized as the cause of significant ecological and economic damage. They also raise a series of less visible social issues. Management of invasive species is often a political process raising questions such as who decides which organisms are to be managed, and who benefits or is affected by different management techniques. In a rural region of northern California, the proposed use of herbicides on spotted knapweed sparked an intense social controversy. This research uses participant observation, interviews, and archival material to understand how members of the Karuk Tribe of California, the non‐Indian community, and the U.S. Forest Service developed different perceptions of safety and risk regarding herbicide use. I describe interconnected factors that frame the interpretation of risk: institutional trust, proximity to exposure, gender, and race. Gender and race, in turn, form the basis of anti‐herbicide mobilization. The larger sociological question highlighted is, who pays the price for species invasions? Use of herbicides on invasive species is increasing. Many people who face increased exposure to herbicides are members of racial minority groups. When the poor or racial minorities face disproportionate exposure, differences in risk perception become matters of environmental justice. This paper discusses the broader social implications of differences in risk perception among communities and land managers.

A two-agent dynamic model with an invasive weed diffusion externality: An application to Yellow Starthistle ( Centaurea solstitialis L.) in New Mexico

This paper presents a bioeconomic model for two agents, a cattle rancher and a non-rancher, with interdependencies between their individual effort of invasive weed management and profitability. Dynamic simulations allow us to find numerically the optimal effort of weed control over a 5-year time horizon under a variety of beginning infestation levels. In a base-case scenario without governmental cost-share of control costs, we find that efforts to control the weed are not profitable. The base-case scenarios also indicate that grazing contributes to giving the invasive weed a competitive edge. A second series of simulations include incentive payments for weed control which are set at the minimum level required to have a net positive impact on the rancher's profitability. From these simulations, we find that the level of infestation impacts the size of the incentive necessary to get the agent to control the weeds and that the incentive payments impact the level of effort of the rancher. In addition, results reveal that the higher incentive payments for lower levels of weed infestations reduce the total cumulative incentive payments over time. Efficient policies directed towards management of invasive weeds may need to be adjusted for each individual case.

Control of Invasive Weeds with Prescribed Burning

Prescribed burning has primarily been used as a tool for the control of invasive late-season annual broadleaf and grass species, particularly yellow starthistle, medusahead, barb goatgrass, and several bromes. However, timely burning of a few invasive biennial broadleaves (e.g., sweetclover and garlic mustard), perennial grasses (e.g., bluegrasses and smooth brome), and woody species (e.g., brooms and Chinese tallow tree) also has been successful. In many cases, the effectiveness of prescribed burning can be enhanced when incorporated into an integrated vegetation management program. Although there are some excellent examples of successful use of prescribed burning for the control of invasive species, a limited number of species have been evaluated. In addition, few studies have measured the impact of prescribed burning on the long-term changes in plant communities, impacts to endangered plant species, effects on wildlife and insect populations, and alterations in soil biology, including nutrition, mycorrhizae, and hydrology. In this review, we evaluate the current state of knowledge on prescribed burning as a tool for invasive weed management.

Games People Play: Human Behavior and Invasive Weed Management

Games people play: human behavior and invasive weed management. DOI:10.2458/azu_rangelands_v27i6_mccoy

A model for predicting invasive weed and grass dynamics. II. Accuracy evaluation

The impact of invasive weed management on plant community composition is highly dependent on location-specific factors. Therefore, treatment means from experiments conducted at a given set of locations will not reliably predict community response to weed management elsewhere. We developed a model that rescales treatment means to better match local conditions. The goal of this paper was to determine if this rescaling improves predictions. We used our model to predict leafy spurge stem length density and grass biomass data from field experiments. The experiments consisted of herbicide-treated plots, untreated controls, and, in some cases, grass seeding treatments. When herbicides suppressed leafy spurge, the model explained 21 to 48% more variation in grass response than did mean grass response to the same or similar herbicide treatments applied at other sites. When herbicides killed grass, the model explained 53% more variation in leafy spurge response than did mean leafy spurge response to the same herbicide treatment applied at other sites. We regressed model predictions against observed data and tested the null hypothesis that resulting slope terms were equal to 1.0. Because the null hypothesis was rejected in two of four tests, the model may systematically over- or underpredict in some situations. However, measurement error in the observed data, unintended herbicide injury, or an inaccurate allometric relationship may account for a major proportion of the systematic deviations, and these factors would not cause prediction error in some management applications. Because the model tends to be better than the means from experiments at predicting plant community composition, we conclude that the model could advance managers' ability to predict plant community responses to invasive weed management.

A model for predicting invasive weed and grass dynamics. I. Model development

Invasive weed managers are presented with a complicated and ever-enlarging set of management alternatives. Identifying the optimal weed management strategy for a given set of conditions requires predicting how candidate strategies will affect plant community composition. Although field experiments have advanced our ability to predict postmanagement composition, extrapolation problems limit the prediction accuracy achieved by interpreting treatment means as predictions. Examples of extrapolation problems include nonlinear relationships between competing plants, site-to-site variation in plant population growth rates, and the carrying capacities of desired species and weeds. Our objective was to develop a model that improves predictions of weed management outcomes by overcoming a subset of these problems. To develop the model, we used data from two field experiments in which four Kentucky bluegrass, six western wheatgrass, and six invasive plant (i.e., leafy spurge) densities were combined in field plots. Graphs of our model's predictions vs. observed field experiment data indicate that the model predicted the data accurately. Our model may improve predictions of plant community response to invasive weed management actions.

History and success of plant pathogens for biological control of introduced weeds in Hawaii

The economic value of biological control of introduced, invasive weeds in Hawaii with fungi is estimated to surpass $100 million. The history of biological control of invasive introduced weed species with fugal pathogens in Hawaii began in 1967 motivated by the request of a Kauai rancher whose pastures were infested with ‘Kolomona,” Senna surattensis . A disease of unknown origin present in his ranch was studied. This led to the first successful control of an invasive species in the Islands by wound-inoculating the isolated pathogen, an Acremonium sp., on the weed in 1968, which killed ‘Kolomona’ in more than 10 ha of land. Hamakua ‘Pa-makani,’ Ageratina riparia , was the most serious invasive weed of range and forests of Hawaii in 1973. The release of the white smut Entyloma compositarum from Jamaica in 1975 induced spectacular disease epidemics in the late 1970s, “wiping out the weed.” This specific pathogen cleared ‘Pa-makani’ from more than 200,000 ha of infested rangeland, and kikuyu grass ( Pennisetum clandestinum ) pastures were rehabilitated in less than 6 years, saving the ranchers millions of dollars. These results convinced the Hawaii Department of Agriculture that fungi were a valuable tool in the management of invasive weeds. Koster’s curse, Clidemia hirta , was considered by environmentalists the most serious introduced species in 1984. The specific fungal pathogen, Colletotrichum gloeosporioides f. sp. clidemiae , was introduced in 1985 from Panama, and approved for field inoculations by the Hawaii Board of Agriculture in 1986. Repeated inoculations with this fungus have caused striking decline of the weed in Aiea State Park and Palolo Valley, Oahu. This fungus becomes airborne only during extended windy and rainy periods, which limits its natural distribution. Therefore, repeated applications are required to enhance it as a bioherbicide. Banana poka ( Passiflora tarminiana ), from the Andean region between Colombia and Ecuador, was the most serious invasive species of high-elevation (800–2200 m) forests of Hawaii in 1983. This climbing vine threatened the pristine koa forests of Hawaii, Maui, and Kauai and the numerous endangered species of Hawaii’s flora in the undergrowth. In 1991, Septoria passiflorae was found on infected banana poka seedlings at Ipiales, Colombia. The pathogen was introduced to Hawaii in 1993 for host-range study in a containment laboratory. Host-range studies showed the fungus to be specific only to banana poka. Inoculations by spraying spore suspensions on adaxial leaf surfaces during 1996–1997 in the Hilo Forest Reserve resulted in major epidemics that severely defoliated the vines. One year after inoculations, the weed biomass was reduced from 40 to 60% and by more than 95% five years later. By 2003, banana poka had been eliminated from most forests, except from north Kona, Hawaii where acid rain killed the fungus. Bush lantana ( Lantana camara ) has been in Hawaii since 1858, and the only pathogen that affects the Hawaiian accessions is a Septoria sp., which was introduced from Ecuador in 1984. The US Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) granted permission to use this pathogen for field inoculations at Kokee State Park in 1996. Sites inoculated in 1989–1999 are showing significant decline in the lantana population, and it is expected that effective control of the weed will occur in time.

Games People Play: Human Behavior and Invasive Weed Management

Games People Play: Human Behavior and Invasive Weed Management

Herbicide Effects on Density and Biomass of Russian Knapweed (Acroptilon repens) and Associated Plant Species1

Sustainable invasive weed management must address treatment effects on desired vegetation. Our objective was to determine the influence of clopyralid plus 2,4-D, glyphosate, and fosamine, at various application rates and timing, on the density and biomass of Russian knapweed and desired plant groups growing in association with this invasive weed. In a randomized complete block design with four replications, three herbicides by three herbicide rates by three herbicide application timings and a nontreated control were factorially applied to two sites located along the Missouri River riparian corridor in Montana. Clopyralid plus 2,4-D, glyphosate, and fosamine were applied during the spring rosette stage of Russian knapweed (June), the bud to bloom stage of Russian knapweed (July), or the flowering stage of Russian knapweed (August). Herbicide rates were considered low, medium, and high based on label rates of clopyralid plus 2,4-D, glyphosate, or fosamine. Density and biomass of all species were sampled 3 y...

Strategies for Early Detection—Using the Wildfire Model1

The wildfire model for invasive weed management is a simple yet effective strategic guide framed on the cornerstones of prevention, early detection, timely control, and vegetation restoration. These guidelines are the same fundamental ingredients that make up this nation's formula for effective wildfire management. Just as early detection is critical for success in fighting fires, early detection is also essential for minimizing ecological effects and to control costs associated with new weed invasions. Both active and passive detection are important in wildfire management, and the same is true for invasive weed management. Passive weed detection—the chance discovery of new infestations by individuals pursuing other outdoor activities—can be helpful but is generally haphazard and incomplete. Passive detection alone will almost certainly fail to find many weed infestations until they have grown too large for true eradication. However, passive detection should neither be discouraged nor its value minimized because it can provide a meaningful way to inform and include additional people who otherwise would not be concerned or involved in weed management. Active weed detection consists of periodic field surveys conducted by trained individuals having clearly defined objectives and using sound search and mapping methods. Traditional methods of on-the-ground weed surveys remain important, but new technology such as remote sensing now offers additional options. Systematic field surveys and other early detection efforts are as important to successful weed management as the organized network of fire lookouts and aircraft patrols are to modern wildfire management. Any wildland invasive weed management program that does not include an effective early detection component will most likely fail.

Population Genetics of Invasions: Can We Link Neutral Markers to Management?1

Abstract Molecular data are becoming easier to collect and can help us address many important questions in invasion biology. However, for most organisms, the connection between molecular loci and phenotypic traits is not direct. Here, I review some fundamentals of population and ecological genetics and point out limitations of molecular data, particularly when the data are from loci without a known connection to the phenotype. I then discuss the ways that molecular data may facilitate management of invasive weeds, despite the limitations. Key uses of molecular data in invasive weed management include identifying species, determining their origins, and understanding mechanisms and rates of spread. Additional index words: Biological invasions, ecological genetics, phylogeography. Abbreviations: AFLP, amplified fragment length polymorphisms; cpDNA, chloroplast DNA; RFLP, restriction fragment length polymorphisms.

Prospects for the Management of Invasive Alien Weeds Using Co-Evolved Fungal Pathogens: A Latin American Perspective

Invasive alien weeds pose a serious threat to the biodiversity of natural ecosystems and a significant constraint to agricultural production worldwide. The use of co-evolved natural enemies, a strategy referred to as classical biological control (CBC), has proven to be a potentially efficacious, cost-effective, and safe option for the management of alien weeds. An analysis of CBC of invasive weeds in Latin America is presented, which shows that only 5% of the worldwide releases of agents, overwhelmingly arthropod, have been in this region. Fungal pathogens are increasingly being considered in CBC programmes, and there are now 11 examples of Latin American fungi having been released as biocontrol agents in other regions of the world. In contrast, only three weed pathogens have been deliberately released in the region. Possible reasons for the paucity of CBC programmes in Latin America are presented, despite the presence of a significant number of alien weed species (60 are listed). An analysis of these weeds reveals that many of them could be amenable to control using natural enemies, including nine weed species for which CBC programmes have been successfully implemented elsewhere in the world. In addition, for many of these 60 species, a co-evolved and damaging mycobiota has already been recorded. The prospects for management of invasive alien weeds in Latin America, using co-evolved fungal pathogens, are assessed with particular reference to selected species from the genera Ambrosia, Broussonetia, Calotropis, Commelina, Cyperus, Dichrostachys, Echinochloa, Pittosporum, Rottboellia, Rubus, Sonchus and Ulex.

Knowledge networks: an avenue to ecological management of invasive weeds

Ecological management of invasive weeds will require substantial increases in the application of ecological knowledge and its integration with other forms of knowledge. To enable these increases, we call for purposeful development of knowledge networks in which new knowledge about a complex situation is created by the interaction of different forms of knowledge. We believe that invasive-plant management must be based on a fine-tuning of managed ecosystems, in which operations (e.g., farm activities) are comprehensively adjusted to confront invasives with a wide array of control measures. Land managers must have the primary role in this tuning process because of their holistic knowledge of the ecosystems they manage. Additionally, such ecological management of invasives will require support from new or improved practices in many relevant sectors, e.g., involving extension workers, farm advisors, and researchers of many sorts. Knowledge networks facilitate the creation, application, and integration of knowledge that will be needed to support ecological invasive-plant management. Worldwide, knowledge networks are under very active development as promising solutions to ecological-management challenges. To develop, networks require proactive organization and facilitation. We have developed an experimental knowledge network to facilitate ecological management of field-crop weeds on the basis of collaborative learning groups that help farmers and other professionals develop necessary knowledge. These groups have been favorably evaluated by most participants, and this article describes the results of our project, including our insights into development of such networks.

Uncertainty, Economics, and the Spread of an Invasive Plant Species

The invasion of ecosystems by nonindigenous (nonnative) species is a global economic problem. In the United States alone, rough estimates suggest that environmental damage and other losses from nonindigenous species range from tens to hundreds of billions of dollars per year (Pimentel et al.), though the true value is uncertain. Uncertainty also pervades attempts to identify economically efficient management strategies for any given nonindigenous invasive species. Sources of uncertainty regarding relevant state variables (e.g., the biomass of an invasive plant species in a particular geographic area) include a paucity of data, measurement errors, and substantial variability in intrinsic rates of spread. Significant uncertainty, regarding the impacts of various management measures applied to any invasive species, also exists. In addition, the problem of invasive species management has characteristics that suggest the use of fuzzy logic. Descriptive terms for categorizing the state of an infestation are inherently vague and often depend on sitespecific contexts. For example, one scientist may categorize a particular weed infestation as minimal, while another classifies the same state as highly infested. Such observational categorizations affect management decisions since numerical (objective) measures of the degree of invasion (e.g., a density or percent cover measure) are often completely lacking or based on incomplete field data. Further, any given scientist may classify an infestation of a given density as minimal at one location but high at another, depending on the nature and human uses of the sites. This means that invasions possess the properties associated with fuzzy sets, and are thereby subject to analysis through fuzzy membership functions (see, e.g., Zadeh). In addition, decisions for managing invasive species need to account for fuzzy variables, such as rate of spread, whose values are uncertain. Fuzzy membership functions developed to deal with such variables are different from traditional probability distribution functions (Kosko). The above characteristics of the problem recommend the collection of data, and ultimately the use of a bioeconomic modeling approach that addresses both the stochastic and fuzzy properties of the invasive species' management problem. In this study, we employ insights from fuzzy set theory to develop an expert survey of the spread and damage caused by an invasive plant species that adversely affects rangeland in California and Nevada. The survey instrument is described as are preliminary results based on survey responses to date. In particular, we construct and discuss membership functions describing infestation levels for nonindigenous weed management. Then, we employ a stochastic dynamic programming (SDP) model to identify economically optimal management choices from a portfolio of potential options, with the results compared to those of a program that seeks to eradicate the invasive species. Our approach differs from previous ones in the following ways. First, while a number of dynamic models for invasive weed management decisions have been constructed, most are deterministic (Taylor and Burt; Gorddard, Pannell, and Hertzler; Jones and Medd; Wu; Eiswerth and Johnson). Second, we utilize formally elicited probabilistic expert judgments within an SDP framework for nonindigenous invasive species. Previous studies of weed control decisions utilize SDP (e.g., Pandey and Medd), but apply it to agricultural crop systems for which good data are available, rather than eliciting probabilistic judgments. Third, our application focuses on a non-cropland setting for which data on invasive species state Mark E. Eiswerth is research assistant professor in the Department of Applied Economics and Statistics, University of Nevada, Reno and G. Cornelis van Kooten is professor in the Department of Economics, University of Victoria in Canada. The authors wish to thank Steve Schoenig, Joseph DiTomaso, and Wayne Johnson for suggestions in survey design, and John Zimmerman for research assistance.

Invasive plants: approaches and predictions

AbstractSuccessful management of invasive weeds will require active attempts to prevent new introductions, vigilant detection of nascent populations and persistent efforts to eradicate the worst invaders. To achieve these objectives, invasion ecology offers five groups of complementary approaches. (i) Stochastic approaches allow probabilistic predictions about potential invaders based on initial population size, residence time and number of introduction attempts. (ii) Empirical taxon‐specific approaches are based on previously documented invasions of particular taxa. (iii) Evaluations of the biological characters of non‐invasive taxa and successful invaders give rise either to general or to habitat‐specific screening procedures. (iv) Evaluation of environmental compatibility helps to predict whether a particular plant taxon can invade specific habitats. (v) Experimental approaches attempt to tease apart intrinsic and extrinsic factors underlying invasion success. An emerging theory of plant invasiveness based on biological characters has resulted in several rather robust predictions which are presented in this paper.