Abstract: Weeds are one of the most significant, and controllable, threats to crop production in North America. Monetary losses because of reduced soybean yield and decreased quality because of weed interference, as well as costs of controlling weeds, have a significant economic impact on net returns to producers. Previous Weed Science Society of America (WSSA) Weed Loss Committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative crop yield losses because of weeds across geographic regions and crops within these regions after the implementation of weed control tactics. This manuscript is a second report from the current WSSA Weed Loss Committee on crop yield losses because of weeds, specifically in soybean. Yield loss estimates were determined from comparative observations of soybean yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each US state and Canadian province provided at least...

Abstract: Human-induced soil degradation has led to declining yields and soil fertility in many parts of the world. Conservation agriculture has been proposed as a strategy to ensure more sustainable land use. While conservation agriculture, based on minimum soil disturbance, crop residue retention, and diversification may improve a range of soil characteristics and can be a potential cropping system for improving farmer resilience to climate change, increased weed pressure is often an impediment to its widespread adoption in southern Africa. Weed control under conservation agriculture in other countries has been linked to increased herbicide use, but concerns about herbicide resistance, access to chemicals, and environmental impacts highlight the need for alternative weed control strategies accessible for smallholders. Farmers in semi-arid regions contend with the additional challenge of low biomass production, which may limit the weed-suppressing benefits of permanent soil cover. This paper reviews the regional applicability of various mechanical (manual weeding, weeding using animal traction, weed seed harvest), thermal (soil solarization, weed steaming, flaming), chemical (herbicides, seed coating), and cultural (crop competition, crop residue retention, intercropping, crop rotation) weed control strategies. For each strategy, benefits and challenges were assessed and contextualized with the circumstances of rainfed smallholder farmers in southern Africa. We found that (1) no single solution can solve all weed control challenges under current conservation agriculture systems; (2) success of weed control strategies is largely contingent upon site-specific conditions, including soil type, dominant weed species, and socioeconomic factors; and (3) practices new to southern Africa, such as weed steaming, merit localized research. Previous reviews have addressed various weed control strategies, but a comprehensive review of strategies available to smallholder farmers in semi-arid southern Africa is lacking. Finding a suitable combination of weed control strategies is critical for encouraging smallholder farmers to adopt and maintain conservation agriculture practices.

Abstract: Weeds constitute the largest biotic threat affecting the yield of cultivated plants. While conventional agriculture relies principally on chemicals for weed control, alternative biological methods may be important tools to reduce weed pressure in agroecosystems. Furthermore, as the problem of excessive residue of plant protection agents in agroecosystems and the growing number of herbicide resistant weed biotypes continue to increase, new solutions that have smaller impacts on the environment are becoming increasingly desirable. One promising such method is the use of crops that exert a negative phytotoxic influence on weeds. This natural phenomenon describing the ability of certain plant species to produce compounds that affect the growth of other plants in their surroundings is called allelopathy. Managing weed infestations in cultivated fields by planting allelopathic crops is a sustainable, economic, and environmentally friendly approach that has been strongly articulated in the international arena. Among cultivated crops, sorghum ( Sorghum bicolor (L.) Moench) has been intensively studied because of demonstrated allelopathic potential. This report provides a comprehensive literature review of the applications of sorghum allelopathy in agriculture. A critical analysis of the allelopathic properties of sorghum identified the following areas contributing to its ability to reduce weed infestation in agroecosystems: 1. a large number of compounds produced by sorghum have allelopathic properties, 2. allelopathic compounds can be applied in the form of mixed plant extracts or in combination with herbicides, 3. sorghum extracts have a broad spectrum of activity, 4. sorghum may be used to produce bioherbicides.

Abstract: HWSC systems that target weed seed production during harvest have been in use in Australian crop production systems for over 30 years. Until recently, though, grower adoption of these systems has been relatively low. It is now apparent with the introduction of a range of new weed seed targeting systems that there is renewed grower interest in the use of this approach to weed control. With the aim of determining the current adoption and use of HWSC systems, 600 crop producers from throughout Australia's cropping regions were interviewed on their adoption and use of these systems. This survey established that 43% of Australian growers are now routinely using HWSC to target weed seed production during grain harvest. The adoption of narrow-windrow burning (30%) was considerably greater than the other currently available techniques of chaff tramlining (7%), chaff carts (3%), bale-direct system (3%), and the Harrington Seed Destructor (HSD) (<1%). When growers were asked about their future use of these systems ...

Abstract: Wheat is among the most important cereal and food crops of world and is grown in almost all parts of the world. It is a staple for a large part of the world population. Any decline in wheat yield by biotic or abiotic factors may affect global food security adversely. Weeds are the most damaging pest of wheat causing in total 24% losses in wheat grain yield. In this chapter, we discuss the (i) weed flora in different wheat growing regions of world; (ii) the yield losses caused by weeds in wheat; (iii) the preventive and cultural options for weed management; (iv) physical weed control;(v) chemical weed control; and (vi) integrated weed management strategy in wheat. A critical analysis of recent literature indicated that broadleaved weeds are the most common group of weeds in wheat fields followed by grass weeds, while sedges were rarely noted in wheat fields. Across the globe, the most important weeds in wheat fields were Avena fatua L., Chenopodium album L., Phalaris minor Retz., Galium aparine L., Stellaria media (L.) Vill., and Veronica persica Poir., respectively. Adoption of wise weed management strategies may help control weeds and avoid yield losses. Both preventive measures and cultural practices have proved their significance for improving weed control in wheat; physical and chemical tools are the other options. Moreover, site-specific herbicide application may help to make weed control economical and reduce the herbicide input. Nonetheless, integrated strategies should be opted for effective and ecofriendly weed management in wheat.

Abstract: Soybean field experiments were performed to investigate the weed-suppressing effects of different tillage systems and cover crop mulches at two locations in southwest Germany during 2014 and 2015. The influence of three different tillage systems on weed control efficacy, soybean plant density, and crop yield was determined. In the no-till system (NT), two different cover crops, (rye and barley), were treated by a roller-crimper before soybean sowing. For the reduced tillage system (RT), shallow soil cultivation (7.5 cm depth) using a cultivator after cover crop harvest was performed. The third system was conventional tillage (CT), which used a plow (25 cm depth) without any previous cover crop treatment. Finally, a CT system without weed control was used as a control treatment (C). Weed densities in the field experiments ranged from 1 to 164 plants m−2 with Chenopodium album (L.), Echinochloa crus-galli (L.) P. Beauv., and Sonchus arvensis (L.) as the predominant weed species. No difference in weed suppression was found between the two cover crops. The highest cover crop soil coverage was measured in the NT treatment. The greatest weed density (164 plants m−2) was measured in the untreated control. CT, RT and NT reduced weed density up to 71%, 85%, and 61%, respectively, to C, across both locations and years. Soybean plant density was reduced in NT (−36%) and CT (−18%) based on aimed sown plant density. Highest crop yields up to 2.4 t ha−1 were observed in RT, while NT resulted in lower yields (1.1 t ha−1). Our work reveals the importance of cover crops for weed suppression in soybean cropping systems without herbicide application.

Abstract: The ecology of weeds preventive weed management mechanical weed management chemical weed management herbicide application equipment herbicide formulations, adjuvants, and spray drift management fate of herbicides in the environment biological weed management weed management systems for oil seed crops weed management systems for grain crops weed management systems for pastures and hay crops weed management systems for rangeland weed management systems for horticultural crops weed management systems for turfgrass weed management systems for forest nurseries and woodlands.

Abstract: In Asia, direct-seeded rice (DSR) is becoming popular as an alternative to puddled transplanted rice (PTR) due to its potential to save scarce resources (labor, water, and energy), reduce greenhouse gas emissions, improve soil physical properties, and increase yields in rotational crops. However, weed management in DSR is more difficult because the initial size differential between weeds and rice is small, reducing crop competitiveness and limiting opportunities for selective control measures including flooding. In this context, preventive approaches—those which focus primarily on limiting dispersal and persistence of weed propagules—may play a critical role in complementing the current reliance on curative tactics such as herbicides. Greater understanding and integration of preventive approaches in DSR may reduce the risks of herbicide resistance development, limit adverse effects of herbicides on human health and the environment, and lower the overall weed management costs. However, information on preventive weed management in DSR is relatively limited. Therefore, the central objectives of this review are to: (i) summarize existing knowledge regarding preventive strategies; (ii) discuss key integrated preventive weed management approaches that have the greatest potential for practical application in DSR systems; and (iii) identify knowledge gaps that limit our ability to optimize preventive approaches. Based on an extensive review of existing literature, we conclude that (i) Minimizing weed seed production in the field is critically important for managing weed seedbanks in DSR, but that given seed dispersal in both time and space, prevention of seed production from neighboring bunds, rice–fallow land and irrigation channels bordering DSR areas may be equally important; (ii) Minimizing dispersal of weed seeds into DSR fields may be a practical approach for species that are dispersed primarily by humans (e.g., as contaminants in crop seeds or through irrigation canals), but not for species that are dispersed primarily by other means (wind and birds); (iii) Promotion of seed predation may be a useful strategy in managing certain weed species in DSR—especially where zero-tillage is used—but more research is needed on the identity of seed predators and management factors that promote their activity; (iv) available evidence suggests that the potential for promotion of seed decay is limited in scope but may be valuable for the management of certain relatively nonpersistent weeds in some cropping systems; (v) strategies that stimulate fatal germination of weed seeds (e.g., stale seedbed) appear to be one of the most promising means of prevention in DSR, but increased information on the mechanisms and timing of dormancy release for key species is needed to optimize and enhance the value of this approach; (vi) Prevention of weed germination and emergence in DSR through mulching—especially in zero-till systems—has proven benefits, but its widespread applicability is limited by the economic tradeoffs associated with using mulch as a source of livestock feed; and (vii) development of anaerobic germination (AG)-tolerant rice cultivars and complementary flooding strategies which can tolerate anaerobic conditions/flooding hold great potential for the suppression of weeds in DSR. Successful integration of preventive approaches for managing weeds in DSR will depend on the development of multidisciplinary approaches which are biologically effective, economically feasible, and socially acceptable. Preventive weed control measures alone are unlikely to be sufficient for the effective and economical management of weeds in DSR systems, but their integration with curative approaches should reduce weed management costs and increase both the likelihood of adoption of DSR and the realization of its benefits for food security.

Abstract: The citrus yield in Brazil is not ranked among the best in the world, potentially due to inadequate management by citrus growers. The low adoption of conservation agriculture (CA) techniques and the improper application of herbicides are also well-known problems. Thus, this study evaluated the use of CA techniques, and two Urochloa species (ruzi grass and signal grass) were used as cover crops. Two different types of mowers (ecological, EM; conventional, CM) launched the mowed biomass into different positions within a young Tahiti acid lime orchard (up to four years old). In addition, the integration of glyphosate into this management system was evaluated, with (GLY) and without (NO GLY) glyphosate application. This experiment was conducted across three growing seasons (2011–2014), in Mogi Mirim, Sao Paulo State, Brazil. The cover crop biomass yields and the effects of the mowing treatments, weed density, vegetative growth and fruit yields of the Tahiti acid lime trees were evaluated. In terms of major re...

Abstract: Over the past century, U.S. field crop farmers have controlled weeds with progressively less costly technologies, moving from hoeing and draft cultivation to motorized cultivation to selective herbicides to broad-spectrum herbicides associated with herbicide-tolerant (HT) crops. The advent of herbicides had the effect of reducing both capital and labor costs by reducing the number of field passes required for effective motorized weed control. The advent of HT crops again reduced both labor and capital costs. These innovations have attracted widespread adoption by farmers. Today, HT crops and broad-spectrum weed control are used by virtually all field crop farmers except those producing for markets that will not accept genetically modified crops. The accelerating spread of herbicide-resistant weeds (an adaptive evolutionary response to extensive reliance on a few herbicides) is triggering U.S. farmers to increase and diversify their herbicide use, increasing both financial costs and selected health and environmental risks.

Abstract: Weeds are the major biological constraint in direct seeded rice (DSR) due to the concurrent emergence of competitive weeds, absence of water to suppress weeds at the time of seedling emergence and emergence of difficult to control weeds. Strategies on weed management in direct seeded rice depend on critical period of weed control, weed flora and method to be adopted. In order to achieve the long term and sustainable management of weeds in DSR an integration of different weed management strategies like integrated weed management (IWM) are essential. The literature regarding the critical period of weed control, weed flora and different methods for the sustainable management of weeds in direct seeded rice are reviewed in this paper.

Abstract: Recent developments in weed science and allied aspects have involved several interdisciplinary approaches. In this context, indiscriminate use of herbicides for weed control has become a questionable subject, which besides controlling the weeds, the chemical herbicides are harmful in many ways to soil, crops, other plants and the environment as a whole. Taking into consideration ecologically sound weed management, in modern days the reliance on chemical herbicides has decreased and a shift towards naturally occurring biological herbicides has received great attention throughout the world. Sunflower is an annual dicotyledonous plant, herbaceous, erect, and a native of North America. It is thermo and photo-insensitive, hence it can be grown year round in sub-tropical and tropical countries. Only two spp. Helianthus annuus L. and Helianthus tuberosum are cultivated for food, the remaining spp., are ornamentals weeds and wild plants. However, H. annuus is allelopathic and inhibits the growth and development of other plants thus reducing their productivity. Sunflower is a major oil-yielding crop in India and its cultivation in northwest India started 25 to 30 years ago in areas located in the plains. In this region, rice-wheat rotation became very popular owing to its high yields; however, these crops are highly infested by weeds, thus farmers use herbicides for their control. Hence, this rotation consumes a maximum quantity of herbicides in this region, which has resulted in several problems viz., environmental pollution, human health hazards, and development of herbicide resistance in weeds. Thus, serious ecological questions about the reliance on herbicides for weed control in this rotation have been raised. One of the alternatives to overcome these problems is with the use of allelopathic strategies, including the use of weed-smothering crops for weed management and for the sustainability of agriculture. The field, pot culture, and laboratory studies have shown that inclusion of sunflower crops in rotation and intercropping considerably reduced the weed population in the current and succeeding crops. Rhizosphere soil of sunflower drastically smothered the weed germination, population, and biomass. The residual suppression effect of sunflower also persisted in the next crop up to 75 days. Thus, it is conceptualized that the inclusion of such oilseed crops before the rice crop in the rice-wheat rotation may provide satisfactory weed control in the succeeding rice crops and may minimize the use of herbicides. Likewise, the replacement of sorghum by summer sunflower oilseed crops may also help in the control of summer as well as winter weeds. More studies in this direction may provide avenues for satisfactory weed management in agro-ecosystems and may help to minimize the use of herbicides and thereby pave the way to develop sustainable agricultural practices for biodiversity conservation and enhancing biological integrity.

Abstract: Little is known of glyphosate-induced hormesis in weeds and how this might influence weed management. To test the hormetic effect of low doses of glyphosate on broad-leaved weeds, two experiments were conducted, in the laboratory and the screenhouse. The hormetic effects of glyphosate solution in growth media (0, 65, 130, 250, and 500 g acid equivalent (a.e) ha−1) and foliar spray (0, 4, 8, 16, 32, and 64 g a.e. ha−1) were tested on four broad-leaved weeds (Coronopus didymus, Chenopodium album, Rumex dentatus, and Lathyrus aphaca). Glyphosate solution in the range 65–250 g a.e. ha−1 stimulated the germination and seedling growth of all tested weeds. However, at 500 g a.e. ha−1 inhibition of germination and growth was observed. Foliarly applied glyphosate in the range 4–32 g a.e. ha−1 increased root and shoot length, dry biomass, and seed production ability of all four weeds species; however, the stimulatory response was species dependent. These results indicate that glyphosate hormesis could play ...

Abstract: Productive crop rotations are central to the success of organic production systems. The selection and sequence of crops are determined by a combination of agronomic and economic factors as well as the principles and standards of organic farming. Semi-structured interviews were conducted with sixteen organic farmers in Central-east Sweden to explore the factors that influence the design of crop rotations and the trade-offs between these factors, taking into account the length of time since conversion to organic production. We discerned three crop rotation strategies: strict, flexible and liberal, based on how crop(s) are repeated over time. A major trade-off for arable farmers was between perennial leys to provide nitrogen and control weeds, and the use of more inputs such as purchased nutrients and mechanical weed control to allow continuous cereal production. Critical considerations for livestock farmers were the length of ley for feed production and weed control, cost of re-seeding leys and deci...

Abstract: An increasing water crisis as well as shortage of farm labor farmers in many Asian regions is forcing a shift from puddled transplanted rice to direct-seeded rice. The weeds, however, are a major constraint to the production of direct-seeded rice. In this perspective, a field study was carried out to evaluate various pre- and post-emergence herbicides and different possible integrated weed management practices in zero-till direct-seeded rice. Weed infestation decreased the rice yield by near about 75%. Co-culture rice with Sesbania followed by (fb) pendimethalin fb 2,4-D effectively reduced the total weed population (65.1%) and biomass (86.7%) at 30 days after sowing (DAS). The lowest total weed dry biomass at 60 DAS was recorded from bispyribac-sodium+azimsulfuron-treated plot and such tank mix application of herbicide performed better against diverse weed flora as compared to a single herbicide. Higher yield and more profit from zero-till direct-seeded rice were obtained with the application of ...

Abstract: Glyphosate-tolerant (GT) cotton offers a multitude of benefits such as broad-spectrum and cost-effective weed control, simple weed management, and reduced impact on the environment. However, high adoption rates of GT cotton have led to overreliance on glyphosate in weed management and have decreased the use of other herbicide options and non-chemical weed-management strategies, possibly leading to the emergence of many resistant weeds. Previous surveys in 2006 and 2011 in the cotton-growing regions of New South Wales (NSW) and Queensland, Australia, indicated changes in weed populations over the period and increased prevalence of several weeds. These two surveys indicated increased dominance of Conyza bonariensis, Echinochloa colona, and Chloris virgata in these regions. Periodic weed surveys are necessary to assess weed population dynamics and shifts due to overreliance on glyphosate for weed management. A survey was carried out in the cotton-growing regions of NSW and Queensland in 2014–15, covering 135 fields. Survey results indicated the emergence of volunteer GT cotton as the most common weed present across all of the cotton-growing regions, occurring in 85% of fields, followed by E. colona (67% of fields surveyed), and C. bonariensis and Sonchus oleraceus, which were present in 51% of fields. The most prevalent grass weed after E. colona was C. virgata (37%). Broadleaf weeds Ipomoea lonchophylla and Amaranthus mitchellii were present in 40% and 37% of fields, respectively. Regional-level analysis indicated greater prevalence of Sesbania cannabina and Parthenium hysterophorus in Emerald region of Queensland. Lolium rigidum was present in the Griffith and Warren area of NSW during summer, even though it is a winter weed. The results of this study indicate integration of diversified weed-management options and inclusion of both non-chemical and chemical options because many major weeds observed in this study are tolerant to glyphosate and have already evolved resistance to glyphosate.

Abstract: Harvest weed seed control is an alternative non-chemical approach to weed management that targets escaped weed seeds at the time of crop harvest. Relatively little is known on how these methods will work on species in the US. Two of the most prominent weeds in soybean production in the midsouthern US are Palmer amaranth and barnyardgrass. Typically, when crop harvesting occurs the weed seed has already either shattered or is taken into the combine and may be redistributed in the soil seedbank. This causes further weed seed spread and may contribute to the addition of resistant seeds in the seedbank. There is little research on how much seed is retained on different weed species at or beyond harvest time. Thus, the objective of this study was to determine the percentage of total Palmer amaranth and barnyardgrass seed production that was retained on the plant during delayed soybean harvest. Retained seed over time was similar between 2015 and 2016, but was significantly different between years for only Palm...