Joseph M. DiTomaso’s research while affiliated with University of California, Davis and other places

Rangelands around the world provide economic benefits, and ecological services are critical to the cultural and social fabric of societies. However, the proliferation of invasive non-native plants have altered rangelands and led to numerous economic impacts on livestock production, quality, and health. They have resulted in broad-scale changes in plant and animal communities and alter the abiotic conditions of systems. The most significant of these invasive plants can lead to ecosystem instability, and sometimes irreversible transformational changes. However, in many situations invasive plants provide benefits to the ecosystem. Such changes can result in novel ecosystems where the focus of restoration efforts has shifted from preserving the historic species assemblages to conserving and maintaining a resilient, functional system that provides diverse ecosystem service, while supporting human livelihoods. Thus, the concept of novel ecosystems should consider other tools, such as state-and-transition models and adaptive management, which provide holistic and flexible approaches for controlling invasive plants, favor more desirable plant species, and lead to ecosystem resilience. Explicitly defining reclamation, rehabilitation, and restoration goals is an important consideration regarding novel ecosystems and it allows for better identification of simple, realistic targets and goals. Over the past two decades invasive plant management in rangelands has adopted an ecosystem perspective that focuses on identification, management, and monitoring ecological processes that lead to invasion, and to incorporating proactive prevention programs and integrated management strategies that broaden the ecosystem perspective. Such programs often include rehabilitation concepts that increase the success of long-term management, ecosystem function, and greater invasion resistance.

Woolly distaff thistle is a long-lived winter annual that threatens the ranching and dairy industries within the North Coast counties of California, particularly the organic producers. No peer-reviewed publications have documented effective control options or integrated management approaches for this species. We conducted two experiments, each replicated, in Marin County, California. The first compared several conventional herbicides at two timings and rates, while the second compared a conventional herbicide treatment with organic and integrated organic control methods, including an organic herbicide (mixture of capric and caprylic acids). Results of the conventional herbicide treatments showed most spring applications (March or April) of aminopyralid, aminocyclopyrachlor, clopyralid, and combinations of aminopyralid + triclopyr, or aminocyclopyrachlor + chlorsulfuron had greater than 99% control of woolly distaff thistle with fewer than 1.5 seedlings per 27-m ² plot by the end of the growing season. Higher rates were generally necessary to achieve the same level of control with winter (January) applications. In the organic herbicide treatments, the most consistent treatment was a combination of mowing followed by 9% (v/v) or the organic herbicide. This treatment was slightly less effective compared with aminopyralid but did have better than 95% control of woolly distaff thistle. The results of this study provide control options for both conventional and organic ranching practices where woolly distaff thistle is a problem.

For years, the development of classical biological has proven to be the most cost-effective and environmentally safe management tool for invasive species. Despite this, in the United States there are a number of political, regulatory and institutional challenges associated with the discovery stage, pre-release phase, and post-release monitoring that have restricted the full potential and the long-term success of many classical biological control programs. Among these needs, we provide recommendations for improved prioritization of specific projects, funding concerns, source countries issues, benefits sharing of biological control agents, shipping live agents, regulatory requirements and procedures, and engagement with the environmental community. We believe these recommendations and potential solutions will significantly improve the future effectiveness of classical biological control programs for the management of invasive species within the United States.

Gene flow is a natural process that occurs among sexually-compatible individuals in which cross pollination can result in viable seeds. Gene flow between individuals within and among populations via pollen occurs only when they have concurrent geography, overlapping flowering times, and share common pollinators. Given a population size sufficient to avoid genetic drift, alleles that have neither positive nor negative impact on fitness will persist in the population at an allelic frequency equal to their introduction level. Alleles for genes conferring a fitness effect will be selected naturally for or against depending on the selection pressure. For example, the frequency of alleles conferring disease resistance may increase in the population in generations where a certain pathogen is prevalent but not when it is absent, while alleles conferring herbicide resistance will neither increase nor decrease in the population in areas where the herbicide is not used. Favorable genotypes for a certain trait are usually fixed at a more rapid rate in self-pollinating than in outcrossing species. Genetic and biological features such as polyploidy, fecundity, and generation time also affect shifts in allele frequencies.

Yellowflag iris, native to Europe, is a rhizomatous, emergent, invasive plant found in pond margins, ditches, and other wetland sites in much of the United States. In water depths up to approximately 50 cm, it forms dense stands, which displace native sedges and rushes, reducing waterfowl habitat and water flow. The rhizomes can reach 6 m in lateral spread, making it very difficult to control by mechanical methods. In addition, conventional boom-sprayer applications are often impractical in most aquatic systems. Drizzle application is a technique for directed treatment of hard-to-reach invasive plants. It uses low volumes (26 to 104 L ha —1 ) of concentrated herbicide solution, applied using a spray gun emitting a thin stream of solution with an effective range of 6 m. In this study, conducted along the margins of two ponds at the University of California, Davis, we compared drizzle applications of glyphosate, imazapyr, and triclopyr to applications using a conventional boom sprayer. Although both glyphosate and imazapyr provided excellent control (> 96 %) of yellowflag iris with either treatment technique, only the drizzle treatments of imazapyr at 2.26 and 4.52% ae (10 and 20% product) at spray volumes of 52 and 26 L ha —1 , respectively, were below the maximum labeled rate and still gave > 98 % control. Furthermore, a cost analysis indicated that the most economical application for effective control of yellowflag iris was a drizzle application of imazapyr at 4.52 % ae (20 % product) at 26 L ha —1 . This study demonstrates that drizzle application with imazapyr can be a practical application method for yellowflag iris control in aquatic systems in which broadcast treatments with conventional boom sprayers may be difficult.

Background: Invasive species are one of the greatest economic and ecological threats to agriculture and natural areas in the US and the world. Among the available management tools, biological control provides one of the most economical and long-term effective strategies for managing widespread and damaging invasive species populations of nearly all taxa. Results: Integrating biological control programs in a more complete integrated pest management approach that utilizes increased information and communication, post-release monitoring, adaptive management practices, long-term stewardship strategies, and new and innovative ecological and genetic technologies can greatly improve the effectiveness of biological control. In addition, expanding partnerships among relevant national, regional, and local agencies, as well as academic scientists and land managers, offers far greater opportunities for long-term success in the suppression of established invasive species. Conclusions: In this paper we direct our recommendations to federal agencies that oversee, fund, conduct research, and develop classical biological control programs for invasive species. By incorporating these recommendations into adaptive management strategies, private and public land managers will have far greater opportunities for long-term success in suppression of established invasive species.

Bluegum eucalyptus (Eucalyptus globulus) is a large tree native to Australia that was widely planted throughout California for building and timber, but in many areas has since spread beyond its planted borders and substantially altered wildlands. Due to its fast growth, large size, and reproductive potential, bluegum impacts on native vegetation, wildlife, and ecosystem processes are of concern, particularly in areas with reliable year-round rainfall or fog where it is most likely to spread. Depending on levels of invasion and rate of spread, bluegum may have negative, positive, or neutral impacts on factors such as fire regimes, water and nutrient availability, understory vegetation. Local climate is particularly influential in determining whether or not bluegum is likely to establish and spread. Quantitative estimates of area covered by bluegum, and weed risk assessments that allow for region-specific climatic information and specific management goals to be incorporated, are needed to guide management of currently existing bluegum populations.

Invasive plant response to control efforts is strongly modified by site-specific factors, treatment timing, and environmental conditions following treatment, making management outcomes challenging to predict. Systematic reviews, which involve quantitative synthesis of data, can address this challenge by identifying general patterns of treatment effects across studies and quantifying the degree to which these effects vary. We conducted a systematic review of medusahead (Taeniatherum caput-medusae [L.] Nevski) control treatments that couples a meta-analysis on control data with an assessment of stakeholder needs to identify critical medusahead management knowledge gaps. With the meta-analysis we generated effect size estimates of how combinations of herbicide, burning, seeding, and grazing impacted medusahead on rangeland dominated by either annual or perennial vegetation. All combinations of treatments in both rangeland systems provided significant short-term control of medusahead, although treatment effects were highly transient on perennial rangeland, particularly for seeding treatments. Stakeholders listed grazing as a preferred management tool, and on annual rangeland an almost twofold reduction in medusahead abundance was achieved by timing high stocking rates to match phenological stages when medusahead was most susceptible to defoliation. Insufficient data were available to evaluate effects of grazing on medusahead on perennial rangeland. On the basis of these data and our stakeholder survey, four major information needs emerged, including the need to better understand 1) seedbank response to burning and herbicide treatments, 2) how to optimize grazing animal impacts on medusahead given ranch enterprise constraints, 3) costs and benefits of control and risk of practice failure, and 4) impacts of adaptive management treatments conducted on larger scales and at longer time intervals. Addressing these knowledge gaps should help overcome key ecological and economic barriers inhibiting implementation of medusahead and other invasive plant management programs on rangeland and provide a positive step toward conserving the critical ecosystem services these systems provide.