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The U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed–crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America’s 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency’s national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being.
Several Miscanthus species are cultivated in the U.S. Midwest and Northeast, and feral populations can displace the native plant community and potentially negatively affect ecosystem processes. The monetary cost of eradicating feral Miscanthus populations is unknown, but quantifying eradication costs will inform decisions on whether eradication is a feasible goal and should be considered when totaling the economic damage of invasive species. We managed experimental populations of eulaliagrass (Miscanthus sinensis Andersson) and the giant Miscanthus hybrid (Miscanthus × giganteus J.M. Greef & Deuter ex Hodkinson & Renvoize) in three floodplain forest and three old field sites in central Illinois with the goal of eradication. We recorded the time invested in eradication efforts and tracked survival of Miscanthus plants over a 5-yr period, then estimated the costs associated with eradicating these Miscanthus populations. Finally, we used these estimates to predict the total monetary costs of eradicating existing M. sinensis populations reported on EDDMapS. Miscanthus populations in the old field sites were harder to eradicate, resulting in an average of 290% greater estimated eradication costs compared with the floodplain forest sites. However, the cost and time needed to eradicate Miscanthus populations were similar between Miscanthus species. On-site eradication costs ranged from $390 to $3,316 per site (or $1.3 to $11 m−2) in the old field sites, compared with only $85 to $547 (or $0.92 to $1.82 m−2) to eradicate populations within the floodplain forests, with labor comprising the largest share of these costs. Using our M. sinensis eradication cost estimates in Illinois, we predict that the potential costs to eradicate populations reported on EDDMapS would range from $10 to $37 million, with a median predicted cost of $22 million. The monetary costs of eradicating feral Miscanthus populations should be weighed against the benefits of cultivating these species to provide a comprehensive picture of the relative costs and benefits of adding these species to our landscapes.
Russian-olive is a nitrogen-fixing tree invading riparian corridors in western North America. The premise of revegetation after weed removal is that revegetation is required to return native species to a removal site and that revegetation improves site resistance to invasion or reinvasion via competitive exclusion. Therefore, we expected that revegetation would reduce invasive species cover and increase native species cover compared with non-revegetated controls. Native understory species diversity increased with time since removal. We recorded 18.2 native species in 2012, and 28.2 native species in 2016. Out of 22 planted species, 2 did not establish. Diversity in revegetated plots did not differ from unplanted controls, likely because species spread quickly across plot boundaries. Native perennial grass, seeded species, and annual bromes increased over time, while nonnative forbs and native forbs decreased over time. Only invasive perennial grass cover responded to the revegetation treatment with cover much higher in controls compared with revegetated plots (25.7% vs. 7.7%); this was likely a response to a preplanting herbicide treatment. All categories of species diversity except invasive species diversity increased over time. Only 4% of Russian-olive stumps resprouted in the first year of removal, less than 1% resprouted 2 yr after removal. There was no Russian-olive emergence from seed in the removal year, and seed emergence varied exponentially among following years. Seeded native species did not have trouble establishing once adequate spring moisture occurred in the second growing season after Russian-olive removal, indicating that removal did not present substantial obstacles to successful revegetation. Follow-up control of Russian-olive is critical after initial treatment.
Miscanthus × giganteus, a widely planted biofeedstock, is generally regarded as a relatively low invasion concern. As a seed-infertile species, it lacks a consistent mechanism of long-distance dispersal, a key contributor to invasion rate, and constitutes a low risk for cultivation escape. However, agricultural production shelters plants from stochasticity and increases propagule pressure, enhancing the potential for low-risk species to take advantage of rare dispersal opportunities. Weed risk assessments of M. × giganteus assume the rarity of events such as scouring and flooding that would facilitate secondary dispersal of vegetative rhizome fragments and the long-term sexual inviability of escapes. Combining data from small-scale rhizome fragmentation and movement experiments, and estimates from the literature, we parameterized an individual-based model to examine M. × giganteus spread given three dispersal scenarios. We further evaluated our estimates in response to different field edge buffer widths and monitoring intensities, two key strategies advised for containing biofuel crops. We found that clonal expansion from the field edge alone was sufficient to allow the crop to outgrow buffers of 3 m or less within 11 to 15 yr with low monitoring intensities. Further, models that included the possibility of rhizome dispersal from fields and scouring at field edges demonstrate the potential for long-distance dispersal and establishment with inadequate management. Our study highlights the importance of considering minimum enforced management guidelines for growers to maintain the ecological integrity of the agricultural landscape.