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Weed interference is a major factor that reduces peanut (Arachis hypogaea L.) yield in the United States. Peanut growers rely heavily on herbicides for weed control. Although effective, herbicides are not a complete solution to the complex challenge that weeds present. Therefore, the use of nonchemical weed management options is essential. The literature on weed research in peanut in the past 53 yr in the United States was reviewed to assess the achievements and identify current research gaps and prospects for nonchemical weed management for future research. More than half (79%) of the published studies were from the southeastern United States. Most studies (88%) focused on weed management, while fewer studies (12%) addressed weed distribution, ecology, and competitive mechanisms. Broadleaf weeds were the most frequently studied weed species (60%), whereas only 23% and 19% of the published studies were relevant to grasses and Cyperus spp., respectively. Seventy-two percent of the published studies focused on curative measures using herbicides. Nonchemical methods using mechanical (5%) and preventive (13%) measures that influence crop competition and reduce the buildup of the weed seedbank, seedling recruitment, and weed seed production have received less attention. In most studies, the preventive weed management measures provided weed suppression and reduced weed competition but were not effective enough to reduce the need for herbicides to protect peanut yield. Therefore, future research should focus on developing integrated weed management strategies based on multiple preventive measures rather than one preventive measure combined with one or more curative measures. We recommend that research on mechanical weed management should focus on the role of cultivation when integrated with currently available herbicides. For successful weed management with lasting outcomes, the dominant weed communities of specific target locations should be addressed within the context of climate change and emerging constraints rather than focusing on single problematic species.
Weeds are a fundamental component of agroecosystems and, if not appropriately managed, can cause severe crop yield losses. New perspectives on weed management are required, because current approaches, such as herbicide application or soil tillage, have significant environmental and agronomic drawbacks. We propose the concept of “neutral weed communities,” which are weed communities that coexist with crops and do not negatively affect crop yield and quality compared with weed-free conditions. Management practices that promote neutral weed communities can enable reduced use of herbicides and soil tillage while enhancing ecosystem services and biodiversity. We report scientific evidence of neutral weed communities and survey ecological explanations for why different weed communities have different effects on crop production. We also propose two weed management approaches for attaining neutral weed communities. The first approach aims to maximize weed biodiversity using traditional approaches such as cropping system diversification and integrated weed management. Higher weed biodiversity is associated with lower dominance of competitive weed species that reduce crop yield. The second approach relies on modern tools such as robots and biotechnology to manipulate the density of specific weed species. This approach can remove highly problematic species and minimize niche overlap between the weeds and crops. Given the complexity of interactions among crops, weeds, and other components of the agroecosystem, we highlight the need for multidisciplinary research to illuminate mechanisms that determine the neutrality of weed communities.
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.
Weeds and invasive plants know no borders and have collectively impacted many ecosystems worldwide, including croplands, forests, grasslands, rangelands, wetlands, and riparian areas. Losses continue to mount, affecting yield and productivity, species diversity, and ecosystem services, with both short- and long-term repercussions on the sustainability of plant and animal communities and the livelihoods of many. New and emerging invasive plants, along with many of the most intractable weeds, have undermined even the best control efforts, serving as a reminder of the constant need for improvements in science, application, and technology. One of the main reasons for the success of weeds and invasive plants is their ability to adapt to abiotic and biotic conditions, and research suggests that this will continue with minimal change.
We conducted an online survey of weed scientists in the United States and Canada to (1) identify research topics perceived to be important for advancing weed science in the next 5 to 10 years and (2) gain insight into potential gaps in current expertise and funding sources needed to address those priorities. Respondents were asked to prioritize nine broad research areas, as well as 5 to 10 subcategories within each of the broad areas. We received 475 responses, with the majority affiliated with academic institutions (55%) and working in cash crop (agronomic or horticultural) study systems (69%). Results from this survey provide valuable discussion points for policy makers, funding agencies, and academic institutions when allocating resources for weed science research. Notably, our survey reveals a strong prioritization of Cultural and Preventative Weed Management (CPWM) as well as the emerging area of Precision Weed Management and Robotics (PWMR). Although Herbicides remain a high-priority research area, continuing challenges necessitating integrated, nonchemical tactics (e.g., herbicide resistance) and emerging opportunities (e.g., robotics) are reflected in our survey results. Despite previous calls for greater understanding and application of weed biology and ecology in weed research, as well as recent calls for greater integration of social science perspectives to address weed management challenges, these areas were ranked considerably lower than those focused more directly on weed management. Our survey also identified a potential mismatch between research priorities and expertise in several areas, including CPWM, PWMR, and Weed Genomics, suggesting that these topics should be prime targets for expanded training and collaboration. Finally, our survey suggests an increasing reliance on private sector funding for research, raising concerns about our discipline’s capacity to address important research priority areas that lack clear private sector incentives for investment.
Public concern regarding the use of herbicides in urban areas (e.g., golf courses, parks, lawns) is increasing. Thus, there is a need for alternative methods for weed control that are safe for the public, effective against weeds, and yet selective to turfgrass and other desirable species. New molecular tools such as ribonucleic acid interference (RNAi) have the potential to meet all those requirements, but before these technologies can be implemented, it is critical to understand the perceptions of key stakeholders to facilitate adoption as well as regulatory processes. With this in mind, turfgrass system managers, such as golf course superintendents and lawn care providers, were surveyed to gain insight into the perception and potential adoption of RNAi technology for weed management. Based on survey results, turfgrass managers believe that cost of weed management and time spent managing weeds are the main challenges faced in their fields. When considering new weed management tools, survey respondents were most concerned about cost, efficacy, and efficiency of a new product. Survey respondents were also optimistic toward RNAi for weed management and would either use this technology in their own fields or be willing to conduct research to develop RNAi herbicides. Although respondents believed that the general public would have some concerns about this technology, they did not believe this to be the most important factor for them when choosing new weed management tools. The need for new herbicides to balance weed control challenges and public demands is a central factor for turfgrass managers’ willingness to use RNAi-based weed control in turfgrass systems. They believe their clientele will be accepting of RNAi tools, although further research is needed to investigate how a wider range of stakeholders perceive RNAi tools for turfgrass management more broadly.
Weeds contribute to biodiversity and a wide range of ecosystem functions. It is crucial to map different weed species and analyze their physiological activities. Remote sensing techniques for plant identification, especially hyperspectral imaging, are being developed using spectral response patterns to vegetation for detection and species identification. A library of hyperspectral images of 40 urban weed species in northeast China was established in this study. A terrestrial hyperspectral camera was used to acquire 435 hyperspectral images. The hyperspectral information for each weed species was extracted and analyzed. The spectral characteristics and vegetation indices of different weeds revealed the differences between weed species in the cities of northeast China and indirectly characterized the growth and physiological activity levels of different species, but could not effectively distinguish different species. Five methods—first derivative spectrum (FDS), second derivative spectrum (SDS), standard normal variate (SNV), moving averages (MA), and Savitzky-Golay (SG) smoothing—were used to pretreat the spectral curves to maximize the retention of spectral characteristics while removing the influence of noise. We investigated the application of a convolutional neural network (CNN) with terrestrial hyperspectral remote sensing to identify urban weeds in northeast China. A CNN classification model was established to distinguish weeds from the hyperspectral images and demonstrated a test accuracy of 95.32% to 98.15%. The accuracy of the original spectrum was 97.45%; SNV had the best accuracy (98.15%) and SG was the least accurate (95.32%). This provides a baseline for understanding the hyperspectral characteristics of urban weed species and monitoring their growth. It also contributes to the development of a hyperspectral imaging database with global applicability.
North African knapweed (Centaurea diluta Aiton), cornflower (Centaurea cyanus L.), corn marigold [Glebionis segetum (L.) Fourr.], rigid ryegrass (Lolium rigidum Gaudin), and corn poppy (Papaver rhoeas L.) are weeds of economic importance in the Iberian Peninsula, particularly due to limited herbicide options for effective control. For this reason, information about their seedling emergence has become critical to develop effective integrated management strategies and better time control actions. The aims of this study were to evaluate the effect of seed burial depth and soil disturbance on the emergence of these weed species. Two pot experiments were carried out to (1) quantify seedling emergence at three burial depths (2, 5, and 9 cm) and (2) characterize seedling emergence in response to different frequencies and timings of soil disturbance. Burial depth limited the emergence of G. segetum and P. rhoeas at 5 and 9 cm, respectively; while seedling emergence of C. diluta, C. cyanus, and L. rigidum were reduced by 92%, 90%, and 67% at 9 cm compared with 2 cm, respectively. Two or more sequential soil disturbance events increased total seedling emergence of C. diluta, P. rhoeas, and G. segetum compared with single events, while L. rigidum did not respond to repeated soil disturbance. These results suggest that turning the soil to bury weed seeds down to 5 cm or deeper would be a very effective method to control G. segetum and P. rhoeas and moderately effective to control C. cyanus. Also, the use of a stale seedbed would have some efficacy to reduce P. rhoeas and C. diluta weed pressure within the crop. This study illustrates how differences among species in seedling emergence in response to soil depth and disturbance can determine distinct emergence patterns ultimately influencing the selection of weed control tools and timing.
Cowvine (Ipomoea lonchophylla J.M. Black) is a native and widely spread summer broadleaf weed in Australia. It contains glycoresins, which are toxic to livestock. However, limited information is available on seed germination ecology and growth phenology of this species. A series of experiments were conducted to determine the response of I. lonchophylla to different environmental conditions. Results showed that the primary dormancy exhibited by I. lonchophylla is due to the physical impediment of the hard seed coat. The seed germination percentage was the highest at the constant temperature of 27 C and alternating temperatures of 35/25 C. Germination of I. lonchophylla was not stimulated by light, suggesting that this species is non-photoblastic. Ipomoea lonchophylla germination was intolerant of a medium to high level of salt stress, and germination was completely inhibited at 250 mM NaCl. The emergence of I. lonchophylla was not restricted by seeding depth up to 8 cm, but only 5% emergence was recorded when seeds were planted at a 16-cm depth. The germination percentage was also drastically reduced by 90% to 100% after exposure to either 3 mo in silage, 48-h digestion in steers, or silage plus digestion treatments. The growth and reproductive phenology of I. lonchophylla was affected by emergence time. Plants that emerged in late spring (November 15) were able to produce more berries per plant than those that emerged in midsummer (January 15) in southern New South Wales. Information gained in our study concerning high soil salinity, ensiling, and digestion will help to develop more sustainable and effective integrated weed management strategies for controlling and reducing the spread of this weed.
Growers have been experimenting with cover crop termination timings to maximize weed suppression and potentially reduce herbicide inputs in soybean [Glycine max (L.) Merr.]. A field study was replicated three times from 2018 through 2021 in South Charleston, OH, to evaluate different management strategies involving a cereal rye (Secale cereale L.) cover crop. The objectives were to determine the effects of cereal rye seeding rate (0, 50, and 100 kg ha−1), management program (preplant, postplant, and delayed), and soybean residual herbicide (flumioxazin + chlorimuron ethyl and no herbicide) on cover crop, weed, and soybean parameters. The preplant program consisted of cereal rye terminated 7 d before planting (DBP) + a postemergence application. The postplant program consisted of cereal rye terminated 7 d after planting (DAP) + a postemergence application. In the delayed program, saflufenacil was applied in April and cereal rye was terminated 21 DAP, and there was no postemergence application. Giant foxtail (Setaria faberi Herrm.) density was reduced by the presence of cereal rye, averaged over other factors, regardless of seeding rate. Cereal rye seeding rate did not affect giant ragweed (Ambrosia trifida L.) density. The delayed management program was generally associated with the lowest weed density, but weed density was often similar in the postplant program. Setaria faberi density was lower in treatments that included a residual herbicide. Residual soybean herbicide use did not affect density of A. trifida. Terminating cereal rye after soybean planting resulted in increased soybean yield in 2019 and reduced yield in 2020, compared with preplant rye termination. These data suggest that adjusting the cereal rye management program may have a greater effect on weed suppression than adjustments to seeding rate. Delaying termination of cereal rye can aid in the suppression of weeds, but a comprehensive herbicide program was necessary to provide adequate (>85%) weed control.
Waterhemp (Amaranthus tuberculatus [Moq.] Sauer) escapes are common in midwestern U.S. soybean [Glycine max (L.) Merr.] fields due to the continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system, weed seeds are harvested with the crop grain and spread back on to the field. Harvest weed seed control methods such as chaff lining concentrate weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. Field experiments were conducted in a soybean–corn (Zea mays L.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managing A. tuberculatus seeds. About 70% of the A. tuberculatus seeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of the A. tuberculatus seeds exiting the combine into the chaff line. Although A. tuberculatus population density in 2021 was 76% higher inside the chaff line than outside the chaff line, A. tuberculatus aboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly, A. tuberculatus inside the chaff line had delayed emergence compared with A. tuberculatus outside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayed A. tuberculatus emergence by more than 2 wk compared with A. tuberculatus outside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manage A. tuberculatus, suggesting the possibility of lower overall herbicide use. These results support implementing chaff lining in soybean-based crop systems of the U.S. Midwest to help manage HR A. tuberculatus seedbanks.