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Navua sedge (Cyperus aromaticus), a perennial plant native to Africa, poses a significant weed concern due to its capacity for seed and rhizome fragment dissemination. Infestations can diminish pasture carrying capacity, displacing desirable species. Despite the burgeoning interest in integrated weed management strategies, information regarding the efficacy of competitive interactions with other pasture species for Navua sedge management remains limited. A pot trial investigated the competitive abilities of 14 diverse broadleaf and grass pasture species. The results indicated a range of the reduction in Navua sedge dry biomass from 6% to 98% across these species. Subsequently, three broadleaf species—burgundy bean (Macroptilium bracteatum), cowpea (Vigna unguiculata), and lablab (Lablab purpureus), and three grass species—Gatton panic (Megathyrsus maximus), Rhodes grass (Chloris gayana), and signal grass (Urochloa decumbens) were chosen for a follow-up pot trial based on their superior dry biomass performance. These six species were planted at three varying densities (44, 88, and 176 plants/m2) surrounding a Navua sedge plant. Among the grass pasture species, Gatton panic and Rhodes grass exhibited high competitiveness, resulting in a minimum decrease of 86% and 99%, respectively, in Navua sedge dry biomass. Regarding the broadleaf species, lablab displayed the highest competitiveness, causing a minimum decrease of 99% in Navua sedge dry biomass. This study highlights the increasing efficacy of crop competition in suppressing weed growth and seed production, with the most significant suppression observed at a density of 176 plants/m2. [ABSTRACT FROM AUTHOR]

Echinochloa crus-galli (L.) Beauv. is a stronger competitor of rice for resources than other weeds. An adequate knowledge of the biology, ecology and critical period of competition of E. crus-galli with dry-seeded rice (DSR) is fundamental in designing effective, sustainable and integrated weed management programs. Experiments were conducted in the 2013 dry and wet seasons to determine the effect of two E. crus-galli densities (40 and 80 plants m−2) emerging at four intervals (2, 15, 30 and 45 d after rice emergence, DARE) with and without rice interference on the growth and biomass accumulation of both rice and weed, and the productivity of rice. The E. crus-galli plant height decreased with the interference of rice plants. The maximum height of 115–130 cm and number of tillers of 477–508 m−2 in rice plants were recorded when grown alone, and these growth parameters declined to 105–109 cm and 315–352 m−2, respectively, when rice emerged simultaneously with E. crus-galli. Other rice growth parameters (stem, leaf, panicle and shoot biomass, and leaf area) and grain yield attributes (panicle density, per panicle filled spikelets and grain weight) decreased significantly with increases in E. crus-galli density at the early emergence time. A delay in E. crus-galli emergence from 0 to 45 DARE caused a significant reduction in E. crus-galli biomass, which resulted in less reduction in rice biomass and leaf area index. Rice grain yield, grain weight, and harvest index improved significantly with a delay in weed emergence up to 45 DARE. The highest grain yield was recorded when rice was grown alone (6.8–7.3 t ha−1), which was similar to the yield produced in the plots wherein E. crus-galli sown at 40 plants m−2 (6.9–7.0 t ha−1) and 80 plants m−2 (6.4–6.7 t ha−1) emerged at 45 DARE. The lowest grain yield (4.3–4.9 t ha−1) was recorded in the plots wherein E. crus-galli emerged simultaneously with rice. This study established that E. crus-galli emergence at 45 DARE could not cause an economic yield loss because of less biomass accumulation and lower survival rate. [ABSTRACT FROM AUTHOR]

Context: Knowledge gaps exist for the interference of Avena ludoviciana and Argemone mexicana in chickpea grown in eastern Australia. Aims: This research aimed to examine the effect of different interference levels of A. ludoviciana and A. mexicana for their potential to cause yield loss in chickpea. Methods: Experiments were conducted in a randomised complete block design with five weed infestation levels of both weeds (none, low, medium, high, and very high) in three replications. Key results: Infestations of A. ludoviciana and A. mexicana at 15 and 17 plants m−2 caused an 83 and 48% reduction in chickpea yield, respectively, compared with weed-free situations. Based on the regression model, a 50% yield reduction of chickpea occurred at 10 and 17 plants m−2 of A. ludoviciana and A. mexicana , respectively. Based on the modified hyperbolic model, maximum seed production of A. ludoviciana and A. mexicana in chickpea at an infestation level of 1 plant m−2 was estimated at 366 and 7800 seeds m−2, respectively. At crop harvest, seed retention of A. ludoviciana and A. mexicana was greater than 50 and 90%, respectively. Conclusions: A. ludoviciana and A. mexicana infestation in chickpea caused a substantial reduction in crop yield. High seed retention in A. mexicana and A. ludoviciana in chickpea suggests the possibility to manage these two weeds through harvest weed seed control. Implications: The information generated from this study could help in strengthening integrated weed management in chickpea. Knowledge gaps exist for the interference of Avena ludoviciana and Argemone mexicana in chickpea in Australia. About 50% yield reduction of chickpea occurred at 10 and 17 plants m−2 of A. ludoviciana and A. mexicana , respectively. High seed retention in A. mexicana and A. ludoviciana in chickpea suggests the possibility to manage these two weeds through harvest weed seed control for strengthening integrated weed management. [ABSTRACT FROM AUTHOR]

Knowledge of the germination pattern and seed longevity of Echinochloa colona under field conditions could play a crucial role in effective weed management. Germination patterns of four populations (B17/12, B17/13, B17/7, and B17/25) of E. colona collected from eastern Australia were studied under field conditions for two years. Each population had multiple cohorts, and peak germination occurred in December 2018. Population B17/12 had a lower dormancy level compared with other populations, as 87% of the seeds germinated in the first cohort. Regression analysis revealed that populations B17/12, B17/13, B17/7, and B17/25 required 2130, 3110, 4320, and 6040 cumulative growing degree days (GDD), respectively, for 80% germination. The last cohorts of each population (100% germination) were observed in February 2020. This suggests that the populations of E. colona had innate dormancy, and a proportion of seeds can germinate in the next season. For the seed persistence study, seed bags of three populations (B17/4, B17/26, and B17/35) were exhumed at different intervals at two locations (Gatton and St George) over 30 months to evaluate decay components. Averaged over locations, burial duration, and burial depth, populations behaved similarly for the seed decay component. After 30 months of seed placement at Gatton, viable seeds at 1, 5, and 15 cm burial depths were 8, 26, and 15%, respectively. However, during the same time period at St George, viable seeds at 1, 5, and 15 cm burial depths were 0, 4, and 3%, respectively. These results implied that E. colona seeds persisted for a longer period (>2 years) in the light-textured soil (Gatton), particularly at the 5 cm burial depth. After 30 months of seed placement at Gatton, seeds decayed faster at 1 cm compared with the 5 cm burial depth. The studies demonstrated that seed persistence and germination patterns of E. colona may vary with different soil and agro-climatic conditions. The results suggest that management strategies should be followed to enable early control of E. colona over a three year period and that restricting reinfestation of weed seeds through seed rains could lead to almost complete control of E. colona in the field. [ABSTRACT FROM AUTHOR]

Ageratum conyzoides L. (Billy goat weed; Asteraceae) is an annual herbaceous plant of American origin with a pantropical distribution. The plant has unique biological attributes and a raft of miscellaneous chemical compounds that render it a pharmacologically important herb. Despite its high medicinal value, the constant spread of the weed is noticeable and alarming. In many countries, the weed has severely invaded the natural, urban, and agroecosystems, thus presenting management challenges to natural resource professionals and farmers. Its interference with agricultural crops, grassland forbs, forest ground flora, and its ability to replace native plant species are of serious concern. Therefore, it is pertinent to monitor its continuous spread, its entry into new geographic regions, the extent of its impact, and the associated evolutionary changes. While management strategies should be improvised to control its spread and reduce its adverse impacts, the possible utilization of this noxious weed for pharmacological and agronomic purposes should also be explored. The objective of this review is to provide a detailed account of the global distribution, biological activities, ecological and environmental impacts, and strategies for the management of the agro-environmental weed A. conyzoides. [ABSTRACT FROM AUTHOR]

Increased planting density can provide crops a competitive advantage over weeds. This study appraised the growth and seed production of two noxious grassy weeds, i.e. feather fingergrass (Chloris virgata SW.) and junglerice [Echinochloa colona (L.) Link] in response to different mungbean [Vigna radiata (L.) R. Wilczek] densities (0, 82, 164, 242, and 328 plants m−2). A target-neighbourhood study was conducted using a completely randomized design with five replications, and there were two experimental runs in 2016–2017. The leaf, stem, and total aboveground biomass of C. virgata was 86, 59, and 76% greater than E. colona. For seed production, E. colona outnumbered C. virgata by producing 74% more seeds. Mungbean density-mediated suppression of height was more pronounced for E. colona compared with C. virgata during the first 42 days. The presence of 164–328 mungbean plants m−2 reduced the number of leaves of E. colona and C. virgata by 53–72% and 52–57%, respectively. The reduction in the inflorescence number caused by the highest mungbean density was higher for C. virgata than E. colona. C. virgata and E. colona growing with mungbean produced 81 and 79% fewer seeds per plant. An increase in mungbean density from 82 to 328 plants m−2 reduced the total aboveground biomass of C. virgata and E. colona by 45–63% and 44–67%, respectively. Increased mungbean plant density can suppress weed growth and seed production. Although increased crop density contributes to better weed management, supplemental weed control will be needed. [ABSTRACT FROM AUTHOR]

The occurrence of freezing stress around herbicides application is one of the most important factors influencing their performance. This experiment was performed to evaluate the efficacy of clodinafop-propargyl and 2,4-D plus MCPA (2,4-Dichlorophenoxyacetic acid plus 2-methyl-4-chlorophenoxyacetic acid), the most important herbicides used in wheat fields in Iran, under the influence of a freezing treatment (-4°C). Wheat and its two common weeds, winter wild oat (Avena ludoviciana Durieu) and turnipweed [Rapistrum rugosum (L.) All.], were exposed to the freezing treatment for three nights from 7:00 P.M. to 5:00 A.M. before and after herbicide application, and their response was compared with plants that did not grow under freezing stress. Under no freezing (NF) and freezing after spray (FAS) conditions, winter wild oat was completely controlled with the recommended dose of clodinafop-propargyl (64 g ai ha-1; hereafter g ha-1). However, the survival percentage of winter wild oat in the freezing before spray (FBS) of clodinafop-propargyl 64 g ha-1 was 7%, and it was completely controlled with twice the recommended dose (128 g ha-1). Under NF conditions and FAS treatment, turnipweed was completely controlled with twice the recommended dose of 2,4-D plus MCPA (2025 g ae ha-1; hereafter g ha-1), while there was no complete control under recommended rate. However, in the FBS treatment, the survival of turnipweed was 7% under double dose. The LD50 (dose required to control 50% of individuals in the population) and GR50 (dose causing 50% growth reduction of plants) rankings were NF50, it can be stated that the freezing stress after the spraying of clodinafop-propargyl and before the spraying of 2,4-D plus MCPA would further reduce the efficacy of these herbicides. [ABSTRACT FROM AUTHOR]

Fimbristylis miliacea is becoming a major rice weed in South and Southeast Asia. An understanding of how this weed species competes with rice and how to manage this weed under multiple resource limitations the development of cultural methods is important. Therefore, a study was conducted in greenhouse to determine the effect of varying rice seeding densities (0, 8, and 32 plants pot−1), nitrogen (N) rates (100 and 150 kg ha−1), and water regimes (aerobic and saturated) on rice and F. miliacea growth characteristics and competitiveness under multiple resource limitations under dry-seeded conditions. Both rice and weed were taller in saturated conditions than in aerobic conditions, whereas rice plants were taller than F. miliacea in both water regimes. F. miliacea grown alone had lower leaf and tiller number and less leaf, stem, shoot, root and inflorescence, biomass under saturated conditions than in aerobic conditions. However, when F. miliacea was grown with competition of rice, water regimes did not affect its growth parameters and inflorescence biomass production. N rates affected Rice growth but F. miliacea was not affected. Regardless of water regime and N rate, F. miliacea height (56 and 82%), tiller number (87 and 87%), leaf number (68 and 88%), shoot biomass (98 and 99%), inflorescence biomass (95 and 99.5%), and whole plant biomass (95 and 96%) decreased at rice densities of 160 and 640 plants m−2, compared with F. miliacea grown alone. The results suggest that growth and seed production of F. miliacea can be greatly declined by increasing rice planting density. [ABSTRACT FROM AUTHOR]

Cyperus iria is amongst the most threatening weeds of rice in Sri Lanka, India, Pakistan, and the Philippines. Broad knowledge about the ecology and fecundity of C. iria is important for its effective management. Field studies were conducted over two seasons (wet (WS) and dry seasons (DS)) to investigate the influence of C. iria populations (40 and 80 plants m−2) on its growth, survival, and fertility, with four emergence times, 3, 15, 30, and 45 d after rice emergence (DARE), during 2013. We postulated that (a) higher plant density of this weed would result in more biomass production and viable seeds per unit area, (b) interference of rice would reduce the biomass production and fecundity of this weed, and (c) delaying weed emergence would lead to downsizing of its percent survival and seed bank enrichment in soil. The results indicated that rice interference decreased C. iria growth and seed production as compared with those of plants established without rice interference. A linear decrease in the percent survival of C. iria without rice and a sigmoid decrease with rice were observed during both seasons. Plant height of C. iria was moderately affected up to 30 DARE, and a significant reduction was observed at 45 DARE. There was a linear relationship between C. iria shoot dry weight and seed number plant −1, across-weed density, seeding rate of rice, and emergence time. C. iria seed production, 1000-seed weight, and seed yield were greater when seedlings emerged simultaneously with the rice crop (3 DARE) than when they emerged late. Under rice weed interference growth, the production of viable seeds was completely stopped at 45 DARE. The delay in the emergence of C. iria up to 45 DARE was unable to produce seed in both seasons. The results of the current studies advocate that the emergence, weed biomass, and seed production of C. iria can be checked by adopting suitable cultural weed management practices, which can impede the emergence of weed relative to rice. These practices, enabling the respective crops to be more competitive, will foster integrated weed management approaches, thus offering a key role in seed detection to the soil seed reservoir or pool by notorious weeds in the field. [ABSTRACT FROM AUTHOR]

In most agriculture farmlands, weed management is predominantly reliant on integrated weed management (IWM) strategies, such as herbicide application. However, the overuse and misuse of herbicides, coupled with the lack of novel active ingredients, has resulted in the uptrend of herbicide-resistant weeds globally. Moreover, weedy traits that contribute to weed seed bank persistence further exacerbate the challenges in weed management. Despite ongoing efforts in identifying and improving current weed management processes, the pressing need for novel control techniques in agricultural weed management should not be overlooked. The advent of CRISPR/Cas9 gene-editing systems, coupled with the recent advances in "omics" and cheaper sequencing technologies, has brought into focus the potential of managing weeds in farmlands through direct genetic control approaches, but could be achieved stably or transiently. These approaches encompass a range of technologies that could potentially manipulate expression of key genes in weeds to reduce its fitness and competitiveness, or, by altering the crop to improve its competitiveness or herbicide tolerance. The push for reducing or circumventing the use of chemicals in farmlands has provided an added incentive to develop practical and feasible molecular approaches for weed management, although there are significant technical, practical, and regulatory challenges for utilizing these prospective molecular technologies in weed management. [ABSTRACT FROM AUTHOR]

The rice–wheat cropping system (RWCS) is the backbone of Indian farming, especially in the north-western region. But continuous adoption of the RWCS in northwest India has resulted in major challenges and stagnation in the productivity of this system. Additionally, the Indo-Gangetic Plains of Pakistan, Nepal, and Bangladesh are also facing similar challenges for sustainable production of the RWCS. Several emerging problems, such as the exhausting nutrient pool in soil, deteriorating soil health, groundwater depletion, escalating production cost, labor scarcity, environmental pollution due to crop residue burning and enhanced greenhouse gas emissions, climatic vulnerabilities, and herbicide resistance in weed species, are a few major threats to its sustainability. To address these challenges, a wide range of sustainable intensification technologies have been developed to reduce the irrigation and labor requirements, tillage intensity, and straw burning. Awareness and capacity building of the stakeholders and policy matching/advocacy need to be prioritized to adopt time- and need-based strategies at the ground level to combat these challenges. This review summarizes the current status and challenges of the RWCS in the northwest region of the country and also focuses on the precision management options for achieving high productivity, profitability, and sustainability. [ABSTRACT FROM AUTHOR]

Avena fatua and A. ludoviciana (commonly known as wild oats) are the most problematic winter grass species in fallows and winter crops in the northeast region of Australia. A series of experiments were conducted to evaluate the performance of glyphosate and alternative post-emergence herbicides on A. fatua and A. ludoviciana. This study reports the world's first glyphosate-resistant (GR) biotypes of A. fatua and A. ludoviciana. The glyphosate dose required to kill 50% of the plants (LD50) and to reduce 50% of the biomass (GR50) for the GR biotype of A. fatua was 556 g a.e./ha and 351 g a.e./ha, respectively. These values for A. ludoviciana were 848 g a.e./ha and 289 g a.e./ha. Regardless of the growth stage (3–4 or 6–7 leaf stages), clethodim (120 g a.i./ha), haloxyfop (78 g a.i./ha), pinoxaden (20 g a.i./ha), and propaquizafop (30 g a.i./ha) were the best alternative herbicide options for the control of A. fatua and A. ludoviciana. The efficacy of butroxydim (45 g a.i./ha), clodinafop (120 g a.i./ha), imazamox + imazapyr (36 g a.i./ha), and paraquat (600 g a.i./ha) reduced at the advanced growth stage. Glufosinate (750 g a.i./ha), flamprop (225 g a.i./ha), and pyroxsulam + halauxifen (20 g a.i./ha) did not provide effective control of Avena species. This study identified alternative herbicide options to manage GR biotypes of A. fatua and A. ludoviciana. [ABSTRACT FROM AUTHOR]

Summer grass weed species are a particular problem in the northeast cropping region of Australia because they are prolific seeders and favor no-till systems. Information on weed seed persistence levels can be used for the development of effective and sustainable integrated weed management programs. A field study was conducted over 42 months to evaluate the seedbank persistence of Chloris truncata, C. virgata, Dactyloctenium radulans, and Urochloa panicoides as affected by burial depth (0, 2, and 10 cm). Regardless of species, buried seeds persisted longer than surface seeds and there was no difference in seed persistence between 2 and 10 cm depths. Surface seeds of C. truncata depleted completely in 12 months and buried seeds in 24 months. Similarly, C. virgata seeds placed on the soil surface depleted in 12 months. Buried seeds of this species took 18 months to completely deplete, suggesting that C. truncata seeds persist longer than C. virgata seeds. Surface seeds of D. radulans took 36 months to completely deplete, whereas about 7% of buried seeds were still viable at 42 months. U. panicoides took 24 and 42 months to completely exhaust the surface and buried seeds, respectively. These results suggest that leaving seeds on the soil surface will result in a more rapid depletion of the seedbank. Information on seed persistence will help to manage these weeds using strategic tillage operations. [ABSTRACT FROM AUTHOR]

Chloris virgata has become one of the most difficult glyphosate-resistant (GR) grass weeds in summer fallows in the eastern region of Australia. It germinates in several cohorts following rainfall events; therefore, growers are often tempted to wait for most of the weeds to emerge before herbicide application. However, by that time, some seedlings have reached an advanced stage and there is limited information on the efficacy and reliability of alternate herbicides when targeting large plants of GR C. virgata. A series of experiments were conducted to determine the efficacy of alternate herbicides for the control of GR C. virgata. Haloxyfop (80 g a.i. ha-1) on its own, in mixtures, or sequential applications of haloxyfop and paraquat or glufosinate provided 97 to 100% mortality of the 8–10 leaf stage plants. Glufosinate (1500 g a.i. ha-1) also provided complete control of plants at this growth stage. For larger plants at the 24–28 leaf stage, glufosinate, with or without additional tank-mixed adjuvants, generally did not provide full control, however did show very high levels of biomass reduction and panicle suppression at application rates of 750 or 1500 g a.i. ha-1. Haloxyfop (40 to 160 g a.i. ha-1) and clethodim (180 g a.i. ha-1) on their own achieved 96 to 100% mortality at this growth stage. When applied to large plants (40–50 leaf stage), a tank-mix of isoxaflutole plus paraquat demonstrated significantly higher levels of plant mortality and biomass reduction than either herbicide used alone, and this mixture appears to be synergistic when tested via the Colby equation for synergy or antagonism. Plant mortality was greater (83%) when isoxaflutole (75 g a.i. ha-1) plus paraquat (300 g a.i. ha-1) was taken up through the foliage and soil, compared with the foliage alone. This study identified alternative herbicide options for large plants of GR C. virgata. [ABSTRACT FROM AUTHOR]

Field experiments were conducted in the rice fields of the Malaysian Agricultural Research and Development Institute in 2018 and 2019, to determine the efficacy of two commercial premix herbicides consisting of imazapic and imazapyr at 70:30 (formulation 1) and 30:70 (formulation 2) applied singly or in sequence for control of weedy rice and other rice weeds. Formulation 1 was applied as PRE at the 0 to 1-leaf stage of weedy rice while formulation 2 was applied as POST at the 3 to 4-leaf stage of weedy rice. Formulation 1 applied PRE at 150 g ai ha-1 with or without sequential application of formulation 2 applied POST at 75 or 150 g ai ha-1 provided complete inhibition of weedy rice. The same rate of formulation 1 applied PRE highly reduced weed density and dry weight of Monochoria vaginalis (99%) and Fimbristylis quinquangularis (93%) as compared to weedy check plots. Formulation 2 applied POST at 150 g ai ha-1 providing lower weed density and dry weight reduction of weedy rice (59 to 65%), M. vaginalis (80 to 81%), and F. quinquangularis (56 to 64%) as compared to those observed in formulation 1 applied PRE at 150 g ai ha-1. These results suggest that although formulations 1 and 2 share the same active ingredients, excellent control of weedy rice and rice weeds could only be achieved with PRE application of formulation 1 at 150 g ai ha-1. [ABSTRACT FROM AUTHOR]

Evolution in the seed dormancy depends on the presence of heritable variation in weed populations. This genetic variation in weeds arises because of abundant, grow rapidly, and produce large numbers of off springs. Compared with other plant species, populations of weed species frequently show limited genetic variation in seed dormancy due to colonization, extensive clonal propagation, inbreeding, and the relative environmental homogeneity. Nevertheless, populations of weed species contain substantial store of genetic variation and genetic differentiation for seed dormancy and other reproductive traits because of pervasive feature of widely distributed nature of weed species. As a result, high level of genetic diversity among the weeds is fostered by hybridization, habitat longevity, environmental heterogeneity, outcrossing and large population size. The objective of this review is to update the existing literature concerned with genetic variation in seed dormancy and reproductive traits in weeds. [ABSTRACT FROM AUTHOR]

Ageratum conyzoides L., Tridax procumbens L. and Bidens pilosa L. are well known plant species of the Asteraceae family that are considered weeds in intensive agriculture. These weeds are traditionally known to have medicinal properties and have been used for therapeutic treatments. However, it is only the lack of proper knowledge, awareness and screening that have limited their use in pharmaceutical sectors. This review attempts to consolidate the traditional, phytochemical and pharmacological studies that have been carried out on Ageratum conyzoides L., Tridax procumbens L. and Bidens pilosa L., which we note are widely spread throughout the world. This study was conducted through a coherent search on Ageratum conyzoides L., Tridax procumbens L. and Bidens pilosa L. with respect to traditional uses, phytochemical and pharmacological studies that have been performed on these three agricultural weeds all over the world. An exploration of reported descriptions of the potential medical importance of three agricultural weed species (A. conyzoides, T. procumbens and B. pilosa) has been presented. The present review would encourage further clinical investigations into these three plants and their extracts to more closely define the range of uses of these herbs for clinical applications. This, in turn, would give a clear understanding whether these weed species might be targeted to be conserved in a sustainable manner rather than eradicated. [ABSTRACT FROM AUTHOR]

Crop residue retention could affect the emergence and biomass of weeds in different ways. A summer and winter pot study was conducted to evaluate the effect of different amounts of sorghum and wheat residue on the emergence and biomass of 12 summer and winter Australian weeds. The equivalent amount of sorghum residue to 0, 1, 2, 4 and 6 t/ha was used in the summer study and winter weed seeds were covered with wheat residue equivalent to the amount of 0, 1, 2, 4 and 8 t/ha in the winter study. The emergence and biomass of Amaranthus retroflexus and Echinochloa colona was not affected by sorghum residue treatment. For other summer weeds, the use of the 6 t/ha sorghum residue treatment resulted in 59–94% reductions in biomass compared to no‐sorghum residue retention. Similarly, the application of 8 t/ha wheat residue in the winter study resulted in a reduced biomass of 15–100% compared to no‐crop residue treatment. The results demonstrated the high potential of using crop residues in eco‐friendly weed management strategies, such as harvest weed seed control tactics. [ABSTRACT FROM AUTHOR]

Weeds are a major constraint to crop production and a barrier to human efforts to meet the ever-rising global demand for food, fibre and fuel. Managing weeds solely with herbicides is unsustainable due to the rapid evolution of herbicide-resistant weeds. Precise knowledge of the ecology and biology of weeds is of utmost importance to determine the most appropriate nonchemical management techniques. Raphanus raphanistrum L. is an extremely invasive and noxious weed due to its prolific seed production, allelopathic potential, multiple herbicide resistance and biological potential. R. raphanistrum causes high crop yield losses and thus has become one of the most troublesome agricultural and environmental weeds. R. raphanistrum could exchange pollen with herbicide-tolerant canola and could become an environmental threat. This weed has evolved resistance to many herbicides, and relying exclusively on herbicide-based management could lead to severe crop loss and uneconomical cropping. Although reviews are available on the ecology and biology of R. raphanistrum, significant changes in tillage, weed management and agronomic practices have been occurring worldwide. Therefore, it is timely to review the status of noxious weeds in different agro-ecological zones and management scenarios. This review focuses on the response of R. raphanistrum to different cultural, mechanical, biological, chemical and integrated management strategies practiced in various agro-ecosystems, and its biological potential to thrive under different weed management tactics. In addition, this review facilitates a better understanding of R. raphanistrum and describes how weed management outcomes could be improved through exploiting the biology and ecology of the weed. [ABSTRACT FROM AUTHOR]

Sonchus oleraceus and Rapistrum rugosum are two rapidly emerging weeds of the northern grain region of Australia. To understand the ability of these weeds regarding their germination response to temperature and different soil moisture regimes, experiments were undertaken on the germination of these weeds at varying osmotic potential and temperature regimes. The experiment was conducted as a split‐plot design with alternating day/night temperature regimes (15/5, 20/10, 25/15 and 30/20°C) as a main plot and osmotic potential regimes (0.0, −0.1, −0.2, −0.4, −0.6, −0.8 and −1 MPa) as a subplot. At different temperature regimes, there was 65–91% germination of S. oleraceus in water (0 MPa). There was 0–4% germination at −0.8 MPa and no germination at −1.0 MPa. Osmotic potential values that can cause 50% reduction in germination of S. oleraceus based on a sigmoid regression model ranged from −0.38 to −0.48 MPa. There was 33–81% germination of R. rugosum in distilled water (0 MPa), 1–3% germination at −0.8 MPa and no germination at −1.0 MPa. Osmotic potential values that can cause 50% reduction in germination of R. rugosum based on a sigmoid model ranged from −0.26 to −0.54 MPa. Results of the study were related to the emergence pattern of weeds during field survey and soil moisture profiles estimated by the Australian Landscape Water Balance Model and explain the emergence of these weeds outside the normal seasonal window of prevalence as a response to changes in weather. [ABSTRACT FROM AUTHOR]

Parthenium weed (Parthenium hysterophorus L.) is an emerging weed species in direct-seeded aerobic systems of rice production. This two-year field study was conducted to evaluate the effect of five different densities (0, 5, 10, 15 and 20 plants m−2) of parthenium weed on rice yield and yield-related attributes. Parthenium weed produced ca. 38 to 178% higher biomass at its densities of 10 to 20 plants m−2 as compared to the lowest density of 5 plants m−2. The paddy yield and yield-related attributes were negatively affected with an increase in the parthenium weed density. In both years, the highest reductions in number of rice panicles (14 to 17%), panicle length (10 to 11%), number of grains per panicle (11 to 18%), 1000-grain weight (8 to 21%) and paddy yield (30 to 35%) were recorded at the highest parthenium weed density (20 plants m−2) tested. However, the lower densities of 5 to 15 parthenium weed plants m−2 also caused 11 to 24% and 12 to 26% losses in paddy yield during the years 2016 and 2017, respectively. Therefore, this weed species should be controlled below the density of 5 plants m−2 to avoid the substantial yield losses (over 15%) in direct-seeded rice. [ABSTRACT FROM AUTHOR]

Proper weed management strategies are very essential for sustainable agriculture crop production. Chenopodium murale L. is one of the most problematic weed all over the world. It's an annual herbaceous plant weed found in Pakistan, India as well as other subtropical and tropical parts of Asia. In approximately fifteen Asian countries, C. murale is the most difficult to control in different crops. It influences negatively on the growth of crops and decreases the biological nitrogen fixation (BNF) in legumes. It is a plant that grows quickly and makes tiny seeds. It is easier for C. murale to adapt to different agro-ecological situations because of its fast seed development and predisposition towards herbicide resistance. Several cultural methods, including irrigation, crop rotation, herbicide-tolerant crop types, mechanical weed management, and mulching have been helpful in controlling this weed species, but very few researchers have successfully achieved biological control of C. murale. A promising way of management for C. murale could involve the use of allelochemicals. The control of this weed could differ according to the quantity of herbicides used, the type of crop, the method they are applied, method of use, and the tillage techniques. Understanding C. murale 's ecology, biology, and management strategies is very essential for its proper management. This review provides the better understanding about this weed and provides the different strategies to control this problematic weed species. • Chenopodium murale L. is a challenging weed in sustainable agriculture in Asia. Cultural approaches and herbicides provide effective control options for this weed. • C. murale has a high potential for spreading due to its tolerance to environmental stresses and adaptation to various habitats. Integration of multiple management practices can be an effective way to control C. murale and minimize the risk of herbicide resistance. • Understanding C. murale 's biology will assist in developing better control methods. This review provides insight into one of the most challenging weeds to manage globally. • Better understanding of the Bio-ecology and herbicide resistance in C. murale can aid in developing new herbicides and management strategies. • Various cultural approaches, herbicide-tolerant crop varieties, and mechanical weed control provide effective controls. Biological control of C. murale is limited, but allelochemicals show promise. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: This study takes a whole‐transcriptome approach to assess gene expression changes in response to glyphosate treatment in glyphosate‐resistant fleabane. We assessed gene expression changes in both susceptible and resistant lines so that the glyphosate death response could be quantified, and constitutively expressed candidate resistance genes identified. There are three copies of the glyphosate target site (5‐enolpyruvylshikimate‐3‐phosphate; EPSPS) gene in Conyza and because Conyza bonariensis is allohexaploid, there is a baseline nine copies of the gene in any individual. RESULTS: Many genes were differentially expressed in response to glyphosate treatment. Known resistance mutations are present in EPSPS2 but they are present in a glyphosate‐susceptible line as well as resistant lines and therefore not sufficient to confer resistance. EPSPS1 is expressed four times more than EPSPS2, further reducing the overall contribution of these mutations. CONCLUSION: We demonstrate that glyphosate resistance in C. bonariensis is not the result of EPSPS mutations or overexpression, but due to a non‐target‐site mechanism. A large number of genes are affected by glyphosate treatment. We present a list of candidate non‐target‐site‐resistance (NTSR) genes in fleabane for future studies into these mechanisms. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

In Australia, turnip weed has been rapidly emerging as one of the major weeds in conservation agricultural systems. Germination and emergence of turnip weed were examined for two populations collected from Gatton and St George regions of Australia; two locations with high and low rainfall, respectively. The seeds of turnip weed germinated at all the tested temperatures, but germination was the lowest at 15/5°C, intermediate at 20/10°C and highest at 25/15°C and 30/20°C. The results indicated a high adaptability of turnip weed to warm environmental conditions, although it is a major problem in the winter season. Germination was higher in dark than light/dark regimes except at 30/20°C. Three was a concomitant reduction in germination as the osmotic potential values decreased from 0 to -1.0 MPa. There was 2 and 4% germination at -0.8 MPa for Gatton and St George populations, respectively, and no germination occurred at an osmotic potential of -1.0 MPa. There was a reduction in germination when the sodium chloride (NaCl) concentration was increased from 0 to 150 mM, and no germination was observed at 200 and 250 mM of NaCl. Turnip weed germinated over a broad range of pH (4 to 10). Seedling emergence was higher at 1 cm depth compared to 0.5 cm or at the soil surface. There was 28 and 33% emergence at the surface for the Gatton and St George populations, respectively, compared to 48 and 56% emergence from 1 cm depth for the Gatton and St George populations, respectively and no emergence was observed from 6 cm depth. The results indicated that tillage leading to shallow burial would promote the emergence of turnip weed; on the contrary, tillage that could bury seeds deep into the soil profile might minimise the emergence. Under ideal conditions and lack of integrated weed management programmes, this weed will emerge, set seeds and enrich the soil seed bank and thereby continue to be a problem in the northern grain region of Australia. [ABSTRACT FROM AUTHOR]

Chloris truncata is a significant weed in summer crops in the subtropical region of Australia. A study was conducted to evaluate the effect of environmental factors on germination and emergence of two populations of C. truncata. Overall, germination was not affected by the populations. Seeds germinated at a wide range of alternating day/night temperatures, suggesting that seeds can germinate throughout the spring, winter and autumn seasons. Seed germination was stimulated by the presence of light; however, 51 to 71% of these seeds still germinated in the dark. The sodium chloride concentration and osmotic potential required to inhibit germination of 50% of the population were 179 mM and -0.52 MPa, respectively. A high proportion of seeds germinated over a wide pH range (4 to 10). Seeds placed on the soil surface had greatest germination (67%) and a burial depth of 3 cm resulted in complete inhibition of emergence. The sorghum residue amount required to reduce emergence by 50% was 1.8 t ha-1. The results suggest that, although this weed will be favored in no-till systems, residue retention on the soil surface will help in reducing its infestation. Seed bank buildup can be managed by burying seeds below the depth of emergence. [ABSTRACT FROM AUTHOR]

Rice is the principal food commodity for millions of people. Its growing demand invokes for an enhanced productivity, but with limited land and water resources. Among various biotic stresses limiting rice yields, the major stress is imposed by weeds, particularly in direct-seeded rice (DSR) under aerobic situations. In weedy situations, the yield losses may ascend to 50–60% in puddled transplanted rice and 70–80% in DSR. Herbicidal weed management is the most widely adapted strategy, however, the large scale application of herbicides mainly of same or similar mode of action is constrained by the risks of environmental trade-offs, introduction of herbicide-resistance in different bio-types of weeds, non-selectivity and narrow-spectrum of herbicides. Hence, ecological approaches, like weed-competitive cultivars, alterations in seed rates, and planting patterns could be highly useful in reducing the weed menace. This review reveals that main characteristics imparting weed-competitiveness to rice include selection of cultivars, seedling vigour, early and faster establishment of seedlings, root-shoot characteristics, and self-supportive allelopathy. In DSR, a higher seeding rate of 50–60 kg ha −1 has been found to reduce weed biomass by ∼50%, without imposing any yield penalty and, thus desirable under weedy conditions. Similarly, a narrow row spacing of 15–25 cm in DSR and 20 × 10 cm in puddled transplanted rice resulted in higher productivity with minimum weed infestations. Although all such practices are not sufficient enough to suppress weeds completely, they are useful in reducing the herbicide dose up to 50% on 158 m ha area under rice cultivation in the world, thereby, reducing huge environmental trade-offs. [ABSTRACT FROM AUTHOR]

Agriculture occupies an important place in improving the living standards of farmers in Pakistan. About 90% of farm earnings rely on the cultivation of sugar, fibre, cereals and legumes. Due to lack of essential resources and technical expertise, every year thousands of farmers fail to reach maximum yield potential. Over 70% of farmers own less than 5 ha in Pakistan; therefore, it is uneconomic to employ costly mechanical and chemical strategies for the control of pests in their crops. Among these pests, we eds are considered to be the major obstacle to crop production, and can ultimately result in crop failure. Traditionally, manipulation of cropping techniques was employed for the control of weeds; later on, development of synthetic chemical herbicides made it easier to control weeds in a very short time period. However, over time the increased use of herbicides has led to the development of herbicide resistant weeds. Furthermore, increasing environmental concerns, weed population shifts, and increased managerial costs have made it difficult for farmers to control these weed species within their limited economic resources. Nowadays, scientists and research organizations are being urged to provide innovative weed management solutions, with minimal ecological impacts. Studies have revealed the importance of cultural strategies for the management of weeds in different cropping systems. Research has proved that alternation of cultural practices, and selection of competitive crop cultivars, could be a possible strategy to minimize the competitiveness of weeds. Increased crop densities, narrower row spacing, intercropping and alternation in row directions are among the weed control strategies gaining rapid attention in many countries. Unfortunately, limited information is available about weed management using crop competition in Pakistan. This review article focusses on the importance of these agronomic practices in reducing the competitive potential of weeds, for their effective and appropriate management in major crops of Pakistan. It is intended to assist researchers in the design of economically viable and eco-friendly weed management strategies, which will aid in eliminating the burden of herbicides and mechanical cultivation from farmer’s production costs. [ABSTRACT FROM AUTHOR]

A great deal of work has been done to explore the hormetic potential of various herbicides to enhance crop growth and yield. However, the growth stimulatory potential of plant-released phytotoxins at low rates to enhance crop yield has not yet been realized, as most of the research has focused on the herbicidal potential of these phytotoxins. However, hormesis of plant-released phytotoxins is a more practical aspect, as these are present at low concentrations in field conditions. These phytotoxins are biodegradable and safe for the environment, and have the potential for crop enhancement both under controlled and field conditions. Low doses of plant-released phytotoxins have been reported to enhance crop growth by up to 50% under controlled conditions, and crop yield by up to 42% under field conditions. In this review, we have discussed hormesis of plant-released phytotoxins with examples. In addition, we discuss the potential for crop enhancement, the influence of different factors on the expression of hormesis, as well as the potential for both undesirable (in weeds) and desirable hormesis (in crop plants). The use of plant-released phytotoxins as growth regulators is also discussed, focusing on sustainable crop production. In future, phytotoxins may be utilized as a crop stimulator to enhance crop yield, especially in organic crop production systems. [ABSTRACT FROM AUTHOR]

Weeds are a major constraint to crop production, and are responsible for considerable yield losses in maize production systems throughout the world. Herbicides are widely used for weed control in maize production systems, but can have negative environmental consequences. Researchers have evaluated the use of crop competition and suppression to manage weeds in various crop combinations, including maize-based systems. Crop competition in maize may involve techniques such as reduced row spacing, increased planting density, and the use of competitive cultivars that exhibit weed suppressive potential. In this review, examination of the literature has revealed the considerable value of using crop competition in integrated weed management programs. Research has demonstrated that narrowing row spacing to half the standard distance reduced weed biomass by 39–68%, depending on weed species. Researchers have also demonstrated that increasing maize planting density by up to twice the standard rate achieved a reduction in weed biomass of 26–99%. While little research has been conducted into the use of competitive maize cultivars for weed management, several studies have documented cultivars with potential to suppress weeds. Attributes of weed competitive cultivars include high leaf area index, and other elements of leaf architecture that improve light interception by the crop, so increasing the shading of weeds. Combining crop competition methods with other agronomic practices can increase their effectiveness in controlling weeds. For example, biomass of Setaria italica (L.) Beauv was reduced by 60% when maize planting density was increased by 1.5 times the recommended spacing, and this effect was more pronounced when fertilizer was banded rather than broadcast. In summary, the strategic use of crop competition to control weeds has been a success in many regions, and is an important tool in integrated weed management. The importance of crop competition methods has particular relevance where farmers are unable to afford herbicides, as making use of crop competition is more economical. [ABSTRACT FROM AUTHOR]

The study evaluated the effects of pre-emergence herbicides and their rates [oxadiazon (0.5 and 1 kg ai ha −1 ), pendimethalin (1 and 2 kg ai ha −1 ), and pretilachlor with safener (0.6 kg ai ha −1 )], and time of soil saturation establishment after herbicide application [1, 3, 5, and 7 days after spray (DAS)] in controlling the six major rice weeds, and their phytotoxic effects on rice seedling growth. All herbicides provided 100% control of Echinochloa colona , Echinochloa crus-galli , Leptochloa chinensis , Cyperus iria , and Amaranthus spinosus . Murdannia nudiflora was 100% controlled by oxadiazon and pretilachlor with safener, but poorly controlled (22–75%) by pendimethalin. Pendimethalin at 2 kg ai ha −1 was more effective than at 1 kg ai ha −1 in reducing the biomass of the stem, leaf, and root of M. nudiflora irrespective of timing of soil saturation. Rice plant height was reduced to a maximum (77–96%) by pendimethalin at 2.0 kg ai ha −1 followed by oxadiazon at 1.0 kg ai ha −1 (38–70%) compared to the non-treated control. In contrast, the tallest rice plants were observed in the non-treated control and those treated with pretilachlor with safener which had 80–100% rice plant survival. The lowest rice plant survival of 0, 6, 7, and 16% was found in the soil applied with pendimethalin at 2 kg ai ha −1 and saturated at 1, 3, 5, and 7 DAS, respectively, which was followed by oxadiazon at 1 kg ai ha −1 . All herbicides except pretilachlor with safener reduced SPAD values with early soil saturation, which improved with delay in soil saturation timing. Pendimethalin at 2 kg ai ha −1 reduced the SPAD values of rice plants by 100–164% relative to the non-treated control and produced the highest phytotoxicity symptoms. Pendimethalin also reduced rice shoot biomass more than oxadiazon, which was compounded by early soil saturation after herbicide application. Pretilachlor with safener was the only herbicide that exhibited low phytotoxic symptoms on rice plants and did not reduce leaf, stem, root, and shoot biomass of rice. Percent reduction in rice leaf, stem, root, and shoot biomass by the different herbicides was in the order of pendimethalin 2 > oxadiazon 1 > pendimethalin 1 > oxadiazon 0.5 > pretilachlor with safener 0.6 kg ai ha −1 . Each herbicide treatment reduced rice growth parameters as soil saturation was delayed in the order of 1 DAS > 3 DAS > 5 DAS > 7 DAS. The study suggests that soil water content and herbicide rates are important factors in influencing herbicide phytotoxicity in rice. The application of herbicides should be avoided when the soil is too wet, and irrigation should be delayed at least one week after herbicide application. [ABSTRACT FROM AUTHOR]

Aerobic rice systems can substitute the conventional rice cultivation system in the wake of water shortage and energy crises. The major constraint in the success of aerobic rice is high weed infestation. Hence, we have discussed the weed flora, yield losses, herbicide-resistant weeds, need for integrated weed management, and approaches to manage weeds in aerobic rice systems. A review of several studies indicated that 90 weed species were competing with rice under aerobic systems, causing 23–100% reductions in grain yield. Weed control in aerobic rice gets difficult due to shifts in weed flora and herbicide resistance development in weeds. A wide increase in grain yield (15–307%) by implementing different weed control practices elaborates the scope of weed management in aerobic rice. Practices, such as soil solarization, sowing of competitive crop cultivars, stale seedbed preparation, mulch application, correct fertilization, and intercropping, were found to have particular significance for managing weeds in aerobic rice systems. Moreover, hand weeding and mechanical control were more effective when combined with other weed control methods. Herbicides, such as pendimethalin, 2,4-D, penoxsulam, ethoxysulfuron, bispyribac-sodium, triclopyr, imazosulfuron, bensulfuron, pretilachlor, and metsulfuron, were found most effective in aerobic rice systems. Keeping in view the severity of weed infestation in these systems and the evolution of herbicide resistance, reliance on a single control method is out of question. Hence, the approach of integrated weed management is the most appropriate for proper weed management and the subsequent success of rice cultivation using aerobic systems. [ABSTRACT FROM AUTHOR]

Reducing crop row spacing and delaying time of weed emergence may provide crops a competitive edge over weeds. Field experiments were conducted to evaluate the effects of crop row spacing (11, 15, and 23-cm) and weed emergence time (0, 20, 35, 45, 55, and 60 days after wheat emergence; DAWE) on Galium aparine and Lepidium sativum growth and wheat yield losses. Season-long weed-free and crop-free treatments were also established to compare wheat yield and weed growth, respectively. Row spacing and weed emergence time significantly affected the growth of both weed species and wheat grain yields. For both weed species, the maximum plant height, shoot biomass, and seed production were observed in the crop-free plots, and delayed emergence decreased these variables. In weed–crop competition plots, maximum weed growth was observed when weeds emerged simultaneously with the crop in rows spaced 23-cm apart. Less growth of both weed species was observed in narrow row spacing (11-cm) of wheat as compared with wider rows (15 and 23-cm). These weed species produced less than 5 seeds plant −1 in 11-cm wheat rows when they emerged at 60 DAWE. Presence of weeds in the crop especially at early stages was devastating for wheat yields. Therefore, maximum grain yield (4.91 t ha −1 ) was recorded in the weed-free treatment at 11-cm row spacing. Delay in time of weed emergence and narrow row spacing reduced weed growth and seed production and enhanced wheat grain yield, suggesting that these strategies could contribute to weed management in wheat. [ABSTRACT FROM AUTHOR]

Due to the overdependence on glyphosate to manage weeds in fallow conditions, glyphosate resistance has developed in various biotypes of several grass weeds, including Chloris virgata Sw. The first case of glyphosate resistance in C. virgata was found in 2015 in Australia, and since then several cases have been confirmed in several biotypes across Australia. Pot studies were conducted with 10 biotypes of C. virgata to determine glyphosate resistance levels. The biotypes were identified as either susceptible, moderately resistant or highly resistant based on the glyphosate dose required to kill 50% of plants. Two glyphosate-susceptible (GS) and two glyphosate-resistant (GR) biotypes were identified by the dose-response study and analyzed for the presence of target-site mutation in the 5–enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Performance of alternative herbicides to glyphosate as well as the double-knock herbicide approach was evaluated on the two GS (Ch and SGM2) and two GR (SGW2 and CP2) biotypes. Three herbicides, clethodim, haloxyfop and paraquat, were found to be effective (100% control) against all four biotypes when applied at the 4–5 leaf stage. All the sequential herbicide treatments, such as glyphosate followed by paraquat and glufosinate-ammonium followed by paraquat, provided 100% control of all four biotypes of C. virgata. This study identified effective herbicide options for the control of GR C. virgata and showed that target-site mutations were involved in the resistance of two biotypes to glyphosate (SGW2 and CP2). Results could aid farmers in selecting herbicides to manage C. virgata in their fields. [ABSTRACT FROM AUTHOR]

Conyza bonariensis, flaxleaf fleabane, is a serious weed in Australian agricultural systems, particularly the north-east cropping system. We present the complete chloroplast sequence ofC. bonariensisreconstructed from Illumina whole genome shotgun sequencing. This is the first complete chloroplast genome available for genusConyza. The complete chloroplast sequence is 153,014 bp long, and has the same gene content and structure as other members of the tribe Astereae. A Bayesian phylogeny of the chloroplast coding regions of 18 representatives of Astereae is presented. TheC. bonariensischloroplast genome is deposited at GenBank under accession number MF276802. [ABSTRACT FROM PUBLISHER]

Wet direct-seeded rice (WDSR) is a method of direct seeding which involves sowing pre-germinated seeds on or into puddled soil. In the wake of water and labor shortages, this method is an effective alternative to the puddled transplanted rice system. Weed infestation has emerged as the major constraint for the success of WDSR as weeds cause more yield loss in this system compared to the transplanting system. The simultaneous emergence of weeds and rice seedlings due to lack of ponding results in heavy weed infestation under WDSR. This has necessitated the use of herbicides for effective and cost-efficient weed control. Pre-emergence (PRE) herbicides, such as butachlor, pretilachlor, oxyfluorfen, pendimethalin; post-emergence (POST) herbicides, such as pyrazosulfuron-ethyl, bensulfuron methyl, bispyribac-sodium, propyrisulfuron, penoxsulam plus cyhalofop-butyl, bispyribac + (chlorimuron plus metsulfuron), bensulfuron methyl plus pretilachlor, pretilachlor plus pyribenzoxim; and pre-plant (PPI) herbicides, such as flufenacet and dimethenamid, have been found to be the most effective herbicides in WDSR when either used alone or as a sequential application of PRE and POST herbicide. However, the indiscriminate use of herbicides has caused the development of herbicide resistance in weeds. Shifts in weed flora and the occurrence of weedy rice are other major challenges associated with WDSR. This paper outlines the currently available weed management options for key production areas of WDSR and enumerates associated challenges and constraints. Recent developments, potential approaches, and cutting-edge techniques have been enlisted along with the identification of future research requirements for weed management in WDSR-based cropping systems. Preventive, physical (manual and mechanical weeding), biological (allelopathy), and cultural (stale seedbed, intercropping, water management, weed competitive cultivar, mulching, manipulation of crop geometry and seeding rate, and fertilization) weed control practices were found to be of vital importance for weed management in WDSR systems. Ultimately, the integration of multiple tactics for a long-term and sustainable weed management program in WDSR is required. Innovative techniques such as nano-herbicides, harvest weed seed control, remote sensing, and precision equipment offer advantageous opportunities for strengthening integrated weed management programs in WDSR. While WDSR is conducive to heavy weed infestation, there remains significant potential to expand the effective implementation of weed management strategies for the overall enhancement of crop yield. [ABSTRACT FROM AUTHOR]

Dry-seeded rice (DSR) is an emerging resource-conserving technology in many Asian countries, but weeds remain the major threat to the production of DSR systems. A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI), Los Baños, Philippines, to evaluate the performance of sole and sequential applications of preemergence (oxadiazon and pendimethalin), early postemergence (butachlor + propanil and thiobencarb + 2,4-D), and late postemergence herbicides (bispyribac-sodium and fenoxaprop + ethoxysulfuron) with different modes of action in comparison to manual weeding in DSR. The sequential applications of all preemergence and postemergence herbicides reduced weed density and biomass by 80–100% compared to the nontreated plots. The sole application of postemergence herbicides reduced weed density by only 44–54% and weed biomass by 51–61%, whereas oxadiazon alone reduced weed density and biomass by 96–100%. All herbicide treatments and manual weeding significantly affected tiller number, biomass, crop growth rate, agronomic indices, yield-contributing parameters (panicle density and filled grains), and yield (biological and grain) of rice. The highest grain yield was obtained in the manually weeded plots (5.9–6.1 t ha −1 ) and the plots treated with oxadiazon alone (5.4–5.6 t ha −1 ) and oxadiazon followed by postemergence herbicides (5.2–5.8 t ha −1 ). The lowest paddy yield (0.22 t ha −1 ) was achieved in the nontreated plots followed by the plots treated with the sole application of bispyribac-sodium and fenoxaprop + ethoxysulfuron. The results suggest that oxadiazon is the best broad-spectrum and economically effective herbicide when applied alone or in combination with other effective postemergence herbicides with different modes of action, depending on the weed species present in the field. [ABSTRACT FROM AUTHOR]

High weed infestation and low nitrogen (N) recovery are among the major causes of lower yield in dry-seeded rice (DSR) compared with transplanted rice. The effects of N rate and planting density dynamics on rice productivity and N-use efficiency (NUE) have been extensively studied in transplanted rice. However, information on the combined impact of N rates, weed regimes, and crop plant densities on rice productivity and NUE is very limited in DSR systems. Attaining synchrony between crop demand and N supply is a key in optimizing the tradeoffs amongst environmental pollution, kernel yield, and profit. Experiments were conducted in 2012 and 2013 to assess the impact of weed regimes (partial weedy and weed-free), N rates (0, 100, 150, and 200 kg ha−1), and rice seeding rates (50 and 100 kg ha−1) on crop productivity, N efficiency indices, and synchronization between crop demand and N supply. The seeding rate of 50 kg ha−1 was better when the sunlight was not a limiting factor. The application of 150 kg N ha−1 produced higher yield-contributing attributes and grain yield (5.2–6.6 t ha−1) of rice than 100 (4.7–5.6 t ha−1) and 200 kg N ha−1 (4.9–6.5 t ha−1). The highest physiological efficiency (40–53 kg grain kg−1 N uptake by plants) was achieved at 150 kg N ha−1. Partial factor productivity was higher in the plots applied with 150 kg N ha−1 than with 200 kg N ha−1. The best degree of synchrony between crop N demand and supply was achieved at 150 kg N ha−1. The results of this study suggest that for harvesting better grain yield, DSR crop should be planted using a seed rate of 50 kg ha−1 in combination with 150 kg N ha−1. [ABSTRACT FROM AUTHOR]

The rice-wheat cropping system is the backbone for food security in all South Asian countries on 13.5 million hectares, except in Sri Lanka, where the rice-rice cropping system is mainly followed. A large proportion of rice and wheat crops is produced as well as consumed in South Asia. Weeds are one of the major biotic factors constraining crop production, affecting crop production both quantitatively and qualitatively. Besides this, while shifting from traditional crop establishment methods (intensive tillage and puddling) to new ones (conservation agriculture practices), a shift in weed flora and its management is an emerging challenge. The use of herbicides is the most economic and effective weed control practice; and therefore, the use of herbicides for weed management is rapidly growing in the world, including South Asia. However, with injudicious use of herbicides, there is a trade-off in terms of resistance development, shifts in weed flora and ecological concerns. However, the evolution of resistance to commonly used herbicides in targeted weed species is the most serious among them. There is diversity of weed species in the rice-wheat cropping system, which has already evolved resistance to a few herbicides in India, Pakistan, and Sri Lanka. Therefore, a proper understanding of herbicide resistance, its evolution, and mechanism is essential. Manual weeding is either not possible, or uneconomical and ineffective due to rising labor shortages and wages. Under such situations, there is an increasing need to integrate and implement different weed management practices, including the sensible use of herbicides along with other control measures, such as adjusting the sowing time, use of weed-competitive cultivars, altering crop establishment methods, tillage practices, crop rotations, optimum use of inputs, in-season crop management practices, etc., to tackle the problem of herbicide resistance. [ABSTRACT FROM AUTHOR]

The authors discuss the effect of climatic changes on cropping systems of wheat and rice in northwest India. They comment that the growth in weeds will lead to losses of about 28-74 percent in rice yields and 15-80 percent in wheat yields. An overview of the need of weed management strategies and conservation agriculture is also presented.