Protein security and sustainable nitrogen cycling in cropping systems in South Asia, Australia, North and South America, the Mediterranean basin,and sub-Saharan Africa are underpinned by grain legumes, such as chickpea (Cicer arietinum), pigeonpea (Cajanus cajan), mungbean (Vigna radiata, also called greengram), urdbean (Vigna mungo, also called blackgram), lentil (Lens culinaris), field pea (Pisum sativum), faba bean (Vicia faba), soybean (Glycine max) and dry/common bean (Phaseolus vulgaris).
       
India is the largest producer, consumer and importer of legume crops, accounting for about 25% of the world’s production, but its productivity is lagging behind several other legume-growing countries. Weeds are always listed as one of the major constraints and can decrease the yield potential of legume crops by up to 90% depending on weed density, weed duration and soil fertility.
       
Weed infestations have been estimated to cause actual economic losses of approximately USD 11 billion annually in 10 major field crops in India (Gharde et al., 2018) and in the United States, Palmer amaranth (Amaranthus palmeri) has been shown to reduce soybean yield by up to 79% and dry bean yield by up to 77% (Frenda et al., 2013), while glyphosate-resistant horseweed (Conyza canadensis) infestations have reduced no-till soybean yields by up to 83% in Brazil and season-long weed competition has reduced chickpea yield by 85% and faba bean yield by 60% in field trials in the Mediterranean region. These findings, from widely divergent production systems, bear witness to the fact that weed interference is not a local but a worldwide problem affecting legume productivity.
       
This review integrates Indian literature (extensively from Indian Journal of Agronomy, Indian Journal of Weed Science and Journal of Food Legumes) with peer-reviewed international literature from Australia, Canada, the United States, Brazil, the Mediterranean region and Africa on weed flora, crop-weed competition, weed management (cultural, mechanical, chemical, biological and integrated), herbicide resistance, rhizobial nodulation and BNF, bioherbicides, climate change interactions and emerging precision technologies.
 
Literature search strategy
 
Literature was identified using structured searches in Google Scholar, ScienceDirect, Springer Link, Wiley Online Library, Cambridge Core, MDPI, Scientific Reports/Nature, SciELO and the reference lists of retrieved review and primary articles (snowball search) of Indian Journal of Agronomy, Indian Journal of Weed Science and Journal of Food Legumes. Search terms included combinations of crop names (chickpea, pigeonpea, mungbean, urdbean, lentil, field pea, faba bean, soybean and dry bean) and weed management terms (weed management, weed control, critical period of weed competition, herbicide, integrated weed management, bioherbicide, allelopathy, herbicide resistance, nodulation, nitrogen fixation, climate change and precision weed management). Literature from 2005 to 2026 was considered, with a strong preference for literature from 2023 to 2026; literature prior to 2005 was included only if it was the primary or original source for a specific finding (e.g., foundational CPWC methodology papers).
       
The inclusion criteria were as follows: (i) peer-reviewed primary research or review articles reporting on weed flora, crop-weed competition, weed-management practice, herbicide performance, nodulation/BNF interaction, bioherbicides, herbicide resistance, climate-change interaction or precision weed management in a grain-legume system; (ii) full bibliographic details (authors, journal, year, volume, pages) independently verifiable at the time of writing.  The exclusion criteria were as follows: studies limited to non-legume crops and not having legume-relevant extension; conference abstracts or preprints without verifiable peer-reviewed publication details; and non-peer-reviewed grey literature, which was deliberately not included in the final reference list even if consulted (Fig 1).


 
Weed flora in legume crops
 
The agro-ecological zone, season and cultural practices have a greater influence on weed flora in legume fields than the legume species alone. Broadleaf weeds, such as Chenopodium album, Convolvulus arvensis and Rumex dentatus, are the predominant weeds in irrigated rabi chickpea in India, where Phalaris minor and Avena fatua are the major grassy weeds that are carried over from rotational wheat. Dactyloctenium aegyptium, Echinochloa colona, Cyperus rotundus and Trianthema portulacastrum are  weeds that compete with kharif legume crops such as mungbean and urdbean (Kumar et al., 2022).
       
The root holoparasite Orobanche crenata (broomrape) is a separate and serious weed problem in Mediterranean and North/East African faba bean, lentil and chickpea and has stimulated a specific breeding programme for tolerant faba bean and lentil lines in Morocco, Egypt, Tunisia and Ethiopia (Negewo et al., 2022). This parasitic weed dimension shows that “weed management” in legumes is not a universal problem, but includes conventional competitive weeds, difficult-to-control grass and broadleaf weeds and, regionally, obligate parasitic plants, which require host resistance as well as purely agronomic solutions.
       
Kochia, wild mustard, Canada thistle and more recently, multiple herbicide-resistant Amaranthus palmeri (Palmer amaranth) are among the most problematic weeds in the United States row-crop systems, particularly for lentil, field pea and dry bean. After 20 years of almost exclusive glyphosate use in glyphosate-resistant soybean, Conyza species (fleabane) Digitaria insularis (sourgrass) and Bidens pilosa are the predominant species in no-till systems in Brazilian soybean.
       
Table 1 summarises the weed flora and reported critical period of weed competition (CPWC)/yield-loss data, expressed in days after sowing (DAS), across the Indian and international range.


 
Crop-weed competition dynamics
 
The critical period of weed competition (CPWC) has been determined for several legumes on several continents and this comparison is instructive. Weed competition even during the first 20 DAS had a measurable effect on crop dry matter in irrigated Indian chickpea and CPWC was extended to 108-119 depending on genotype and season (Hakeem et al., 2025). A separate field study in Iran also revealed a different CPWC window for chickpea using regression-based yield-loss modelling (Mohammadi et al., 2005; Veisi et al., 2019) and an earlier field study in the Mediterranean indicated that the timing of weed removal had significant effects on the productivity of chickpea and lentil (Al-Thahabi et al., 1994). Weed competition had a significant impact on the yield of chickpea and faba bean, reducing yield by approximately 85% and 60%, respectively, in Sicilian field trials, as CPWC occurred earlier in chickpea (261 growing-degree-days after emergence) than in faba bean (428 GDD) because of the more vigorous early growth and higher height of faba bean (Frenda et al., 2013). The Mediterranean CPWC averaged 50-69 days for chickpea at 5% yield loss. Weed-free maintenance is generally adequate until about 60 DAS for pigeonpea (Kaur et al., 2015; Rao and Nagamani, 2010; Vasave et al., 2023) and until 2-5-node growth stage for Western Canadian lentil (Fedoruk et al., 2011) -showing that even crops that are generally considered to be poorly weed competitive have a window of time that is manageable and defined. In short-duration Indian legume crops (mungbean and urdbean), weed control takes a disproportionately large amount of the crop life cycle compared to longer-duration crops; thus, the importance of efficient early weed control in these crops is emphasised in Indian literature (Singh et al., 2023) (Fig 2).


 
Weed management approaches
 
Cultural and preventive methods
 
Cultural tactics involve changing the resource capture to the crop community early in the season. Competitive cultivar choice, optimum tillage, sowing geometry, timing, rate and depth, fertiliser placement, irrigation scheduling, intercropping, stale seedbeds and crop rotation. are recommended practices.
       
Crop rotation is an effective weed management tool:  In India, populations of P. minor that would otherwise carry over from wheat to rotational crops of chickpea or lentil are reduced by several seasons of crop rotation with berseem, mustard, or winter maize. In the Mediterranean, fenugreek was intercropped with faba bean, which decreased Orobanche foetida infestation without affecting seed yield (Abbes et al., 2019).
       
Mulching suppresses weeds through light exclusion, physical impedance and chemical suppression (if the mulch is allelopathic). Paddy straw mulch (5 t/ha) + one hand weeding at 30 DAS recorded the lowest weed density and weed dry weight and maximum seed yield in an Indian chickpea trial (Sahu et al., 2024).
       
Similarly, increasing seeding/plant density was effective, with a 16% increase in lentil cut weed biomass with a 1.5 × seeding rate in organic management and Western Canadian field trials have shown that once the crop reached the 2-5 node growth stage, competition from the crop canopy alone was sufficient to suppress further weed emergence (Fedoruk et al., 2011). A Greek chickpea trial that combined a 1.5 × seeding rate with mechanical and herbicide treatments also resulted in improved weed suppression.
       
In general, intercropping legumes with a taller and faster growing companion crop reduces overall weed density and biomass, with less consistent results for weed species diversity. At the crop system level, rice-legume and rice-wheat-legume rotations with better weed management have been found to be more productive and sustainable than conventional rotations without a specific legume-weed-management component in the presence of biotic stress and under nutrient-deficient soils (Rao et al., 2015; Chauhan et al., 2017) and improved weed management has been shown to increase lentil yield under biotic stress and nutrient-deficient soils (Prakash et al., 2019).
 
Mechanical methods
 
Hand weeding and inter-row hoeing are still common where labour is available, but are limited by the availability of rural labour and labour costs at the peak sowing window common to most legumes and pose no risk of crop phytotoxicity or resistance selection.  Hand weddings (one or two) timed to the CPWC (e.g., 25 and 50 DAS in pigeonpea; Ali, 1991) continue to serve as a standard comparison point for chemical weed-control treatments.
       
Mechanical weed control is often less effective than chemical-mechanical combinations in reducing overall weed biomass and requires labour at a critical time in most legume-growing areas, whether in Indian smallholder systems or in labour-limited mechanised systems in North America and Australia.
 
Chemical weed control
 
Pendimethalin is the most common herbicide applied pre-emergence at 750-1000 g a.i. ha^-1 and is used in legume crops worldwide (Vasilakoglou et al., 2013; Jha and Kumar, 2017; Jing et al., 2025) followed by hand weeding or post-emergence herbicide application. In India, kharif legume crops (peanuts, urdbean and mungbean) are recommended to be sprayed with post-emergence imazethapyr (Kumar et al., 2020; Marimuthu et al., 2024), whereas it has been reported to be phytotoxic to the rabi legume crop group (chickpea, lentil and field pea) at lower doses (20-25 DAS) of 50-100 g a.i. ha^-1. This is not just the five or six main legume crops that are usually the focus of herbicide reviews, but also various minor legume crops such as mothbean (Pratap et al., 2018) and French bean (Goud and Dikey, 2016) where herbicide programmes have been standardised for dry matter suppression of weeds.
Indian trials showed that the newer post-emergence broadleaf-active herbicide (20.6-26.7 g a.i. ha^-1, 14-21 DAS) Topramezone lowered total chickpea weed density by 68-70% at 45 DAS and increased seed yield by 15.3-19.6% compared with standard pendimethalin-quizalofop treatments without affecting nodulation or soil esterase activity.
       
To control ALS-resistant Amaranthus palmeri, North American dry-bean producers have used sequential applications of dimethenamid-P, a Group 15 (VLCFA) herbicide, which has a different mode of action from imazamox- and bentazon-based programmes (Miranda et al., 2022). In Brazil, a similar experience of glyphosate-resistant soybean growers shifting to pre-emergence residual herbicides (sulfentrazone, flumioxazin, imazethapyr, chlorimuron and s-metolachlor) and then to glyphosate in the post-emergence stage, due to the selection of glyphosate-resistant Conyza and other weeds (Lopes Ovejero et al., 2013) has been observed.
       
In the case of pre-emergence flumioxazin application in Iran, weed biomass decreased by up to 83% in three provinces, resulting in the highest yield when using the combined application with a single hand weeding (Veisi et al., 2024).
       
Earlier, screening trials in India were conducted in chickpea, in which several new herbicide options were tested; sequential applications of pendimethalin and quizalofop-ethyl resulted in the most consistent weed control and yield advantage over an unweeded check (Kachhadiya et al., 2009). A two-year field evaluation of pre-and post-emergence combinations in Central Punjab, India, revealed that pendimethalin, followed by quizalofop-ethyl, reduced weed density and dry matter in the crop and resulted in the highest seed yield among the evaluated treatments (Kumar et al., 2025).
       
However, not all legumes are tolerant to these herbicides: In-crop tolerance to AHAS inhibitors (imidazolinone) has been introgressed into adapted chickpea and lentil cultivars from breeding programmes in Australia and Canada to broaden the safe in-crop herbicide options.
       
In faba bean and lentil, the parasitic weed Orobanche crenata (Section 3) must also be considered when selecting herbicides and conventional post-emergence herbicide control is minimal when the weed has attached; losses in yield, quality and marketing due to broomrape in lentil alone have been estimated  to be serious throughout the Mediterranean and Middle East (Yolcu et al., 2020), making the development of host plant resistance to broomrape the main management strategy (Rubiales et al., 2009) at present.
       
Table 2 summarises the herbicide dose, timing, HRAC mode-of-action group, crop safety and resistance-risk notes for the principal options discussed above.


 
Integrated weed management (IWM)
 
 IWM-a pre-emergence herbicide plus one timely hand weeding, interculture operations, or post-emergence herbicide is the default recommendation for most legumes and most regions surveyed here (Fig 3) and is estimated to increase legume crop productivity by 20-45% compared to unmanaged or single-tactic control (Mishra and Choudhary, 2026; Rao et al., 2015).


       
In Brazilian soybean, chemical control combined with a green-cover off-season strategy with ruzigrass (Urochloa ruziziensis) provided better control of glyphosate-resistant sourgrass (Digitaria insularis) than herbicide sequences alone (Correia, 2022) and pre-emergence residual herbicide programmes followed by post-emergence glyphosate provided consistent control across nine locations in Brazil without soybean yield penalties (Lopes Ovejero et al., 2013). Pendimethalin alone or in combination with hand weeding at 50 DAS in Indian pigeonpea was superior to other methods (Kaur et al., 2015).
 
Herbicide resistance and weed flora shift
 
Resistance to herbicides in legume-associated weeds is a true global phenomenon and has similar causes: a limited number of modes of action registered for a particular crop group and a reliance on the same mode of action over successive seasons. In India, imazethapyr (an ALS-inhibitor commonly used in mungbean, urdbean and pigeonpea) has been found to have reduced field efficacy against Echinochloa colona and Trianthema portulacastrum in recent seasons and the same chemistry is well documented in the multiple-herbicide resistance of Phalaris minor in the wheat phase of the same rotations, which has developed sequentially from isoproturon (PS-II inhibitor) resistance to ACCase- and ALS-inhibitor resistance over decades. Amaranthus palmeri populations resistant to up to ten different herbicide sites of action, including ALS, PS-II, EPSPS (glyphosate), PPO and HPPD inhibitors, have been confirmed in the United States and yield losses of up to 91% in corn, 79% in soybean and 77% in dry bean have been reported where control fails (Miranda et al., 2022). Nearly 20 years of almost exclusive glyphosate use in glyphosate-resistant soybean (GRSB) have led to the registration of all three major Conyza species infesting soybean as glyphosate-resistant, with some populations also resistant to chlorimuron-ethyl and paraquat (Correia, 2022; Lopes Ovejero et al., 2013). These international cases confirm the same practical message that is being increasingly stressed in the Indian legume crops literature: mode-of-action rotation and sequential/tank-mixed herbicides with different chemistry are the most practical near-term approach to slow the selection of resistant weed populations and this should be done throughout the entire crop rotation, not just the legume phase, as resistant weed populations readily move between rotation phases. The composition of weed flora may also change over time in continuous single-herbicide use (grass-dominated fields becoming broadleaf-dominated after a period of grass-selective herbicide use, or vice versa) and herbicides with soil persistence have a known risk of causing damage to sensitive rotation crops (e.g., imazethapyr and imazamox residues can damage a following mustard or greengram crop if planted too early after application).
 
Effects on nodulation and biological nitrogen fixation (BNF)
 
Because BNF is a central agronomic rationale for growing legumes, herbicide effects on rhizobium-legume symbiosis warrant explicit treatment rather than being folded into general yield outcomes (Fig 4).


       
The nodule number and nodule dry weight were found to be correlated with weed-control efficacy during a field trial of kharif mungbean at Varanasi: the season-long weedy check had the lowest nodule number and nodule dry weight, the twice-hand-weeded had the next lowest and weed-free plots had the highest, followed by post-emergence fenoxaprop-p-ethyl plus chlorimuron-ethyl (Mirjha et al., 2013). This indicates that weed competition, rather than herbicide use per se, was the main factor responsible for the decreased nodulation in that trial and this distinction is important because the two effects can be easily confused. A similar conclusion was reached in a long-term Mediterranean tillage experiment in faba bean, where weed infestation level, rather than tillage system, was the predominant factor accounting for the inter-annual variation in grain yield and symbiotic N2 fixation (Giambalvo et al., 2012).
       
Controlled-environment evidence also indicates that specific compounds, such as pendimethalin at pre-emergence weed control rates reduced the nitrogen-fixation rate by 44% in the common bean (Phaseolus vulgaris) and completely prevented nodulation in alfalfa (Medicago sativa) inoculated with Sinorhizobium meliloti, likely due to changes in root exudate composition and rhizobial growth (Paniagua-Lopez et al., 2023).
       
This suggests caution in timing in relation to the peak rhizobial infection period and the need for ongoing field-level monitoring, even when a compound is nominally labelled as crop-safe, especially when pendimethalin is used, as it is the most widely used pre-emergence herbicide in legume crops worldwide.
       
A recent Indian growth-chamber study on groundnut (Arachis hypogaea) directly relevant to Section 9 below found that elevated CO₂ alone and elevated CO₂ with elevated temperature significantly increased groundnut growth and nodulation, while elevated temperature alone reduced both; Herbicide application at all tested rates reduced rhizobium population, nodulation and chlorophyll content compared to the untreated control and herbicide efficacy was reduced under elevated CO₂, suggesting that future climate scenarios may require re-optimised herbicide doses as well as more attention to impact on nodulation (Sreekanth et al., 2024).
       
It appears that newer chemistries are more promising in this regard. In Indian chickpea trials, topramezone did not exhibit any adverse effects on nodulation or soil esterase activity in comparison to the standard pendimethalin-quizalofop programme. This suggests that herbicide selection can, in principle, be optimised for both weed control and nodulation safety, rather than compromising one.
 
Bioherbicides and sustainable weed management
 
Bioherbicides, weed-suppressive products derived from plants (allelochemicals, essential oils and extracts) or microorganisms (fungal, bacterial and viral phytotoxins), are an emerging research field that is being marketed as a lower-residue, resistance-slowing alternative to synthetic herbicides, but validation in the field, specifically in grain legumes, is limited compared to row crops, such as maize and vegetables.
       
Allelopathic crop residues have been documented to have weed-suppressive effects: sorghum residue (sorgoleone), black mustard (allyl isothiocyanate) and clover species (isoflavonoids, coumarins) have all been shown to suppress weeds such as Cyperus rotundus, Convolvulus arvensis, Chenopodium album, Amaranthus spp. and Phalaris minor when incorporated as mulch or grown in rotation, providing a mechanistic link between the mulching practices described in Section 5.1 and a true allelopathic mode of action rather than simple physical suppression.
       
In contrast to single-site synthetic herbicides, resistance has not been reported against essential oils derived from plants (e.g., Eucalyptus, Rosmarinus and other aromatic plants) because they simultaneously target multiple physiological processes, including disrupting the integrity of weed-seedling cell membranes, inhibiting mitochondrial respiration and DNA synthesis (Hasan et al., 2021). Although registration for grain-legume use is still restricted, a commercial plant-based bioherbicide (WeedLock) has been demonstrated to cause substantial reductions in chlorophyll content and disruption of photosynthesis in a several of weed species within 24 hours of application, demonstrating the practical maturity that some plant-based products have already attained.
       
Microbial bioherbicides, which are mainly fungi (mycoherbicides) but also include a few bacteria and viruses, are used to cause disease in target weeds, not to be directly phytotoxic (Hasan et al., 2021). The use of plant extract or microbial bioherbicides in combination with reduced-rate synthetic herbicides has demonstrated potential for synergism and to reduce the overall chemical load.Integrating bioherbicide delivery with precision-application technologies, as described in Section 10 is an ongoing research topic.
       
In the case of legume systems, the opportunity is not so much in commercial bioherbicide products (few of which are registered for legume crops) but in conscious allelopathic residue management and rotation design, which has already been partially implemented in Indian and Mediterranean cropping systems, but not necessarily in the context of bioherbicides.
 
Climate change and emerging weed challenges in legumes
 
Climate change is projected to impact crop-weed competition through at least four interacting pathways: increasing atmospheric CO₂, rising temperature, changing precipitation patterns and changes in herbicide efficacy, all of which are briefly addressed in respect to legumes.
 
Elevated CO₂ and weed competitiveness
 
The stimulation of photosynthesis and biomass accumulation is greater in C₃ weeds than in many crops under elevated CO₂ and most of the problematic legume-associated weeds (as well as the legumes themselves) are C₃ plants; therefore, the competitive advantage is not uniform and varies with crop-weed pairings.
       
The CPWC was found to shift under elevated CO₂, shortening for some harvestable organs and lengthening for others in a growth-chamber study with radish (Raphanus sativus) and buckwheat (Fagopyrum esculentum) as model crops and weeds, indicating that CPWC recommendations derived under current climate conditions may need periodic revision rather than being considered as fixed agronomic constants (Kubinski et al., 2026).
 
Herbicide efficacy under climate change
 
Rising CO₂ has been demonstrated to reduce the effectiveness of herbicides in several ways: increase in leaf thickness, change in the composition of cuticular waxes, decrease in stomatal density (which decreases foliar herbicide uptake) and a dilution effect due to an increase in the ratio of root to shoot biomass.
       
Increased CO₂ decreased the effectiveness of glyphosate and halosulfuron on purple and yellow nutsedge (Cyperus rotundus and C. esculentus, respectively, which are problematic legume-field weeds) (Marble et al., 2015) and resistance to the ACCase-inhibiting herbicide cyhalofop-butyl in multiple-resistant Echinochloa colona has been demonstrated to be exacerbated by elevated CO₂ and temperature, indicating that climate change may exacerbate, not just coincide with, existing herbicide-resistance issues. A study in India with groundnut revealed that herbicide efficacy decreased with increasing CO₂, with higher herbicide doses required to achieve the same level of weed control (Sreekanth et al., 2024), directly linking the climate-change and nodulation/BNF themes of this review as higher herbicide doses would also increase the risk of nodulation suppression (Section 7).
 
Shifting weed flora and invasive risk
 
Weed distributions are likely to shift poleward and phenology and seed-bank dormancy behaviour will change with increased temperatures and changing rainfall patterns, potentially resulting in new weed problem species in legume-growing areas where they are not currently a problem and allowing C4 weeds  to expand their distribution in currently temperate legume-growing tracts.
       
The new discipline of “weedomics” (the use of genomics, transcriptomics and metabolomics in weed biology) is being touted as a way to predict which weed populations are likely to be the first to adapt to these new conditions and herbicide selection pressure.
       
Collectively, these suggest that CPWC data, herbicide dose recommendations and resistance-monitoring protocols created under current climate conditions will need to be periodically revalidated and that this need is likely to overlap directly with the nodulation/BNF concerns raised in Section 7.
 
Precision agriculture and emerging technologies
 
In row crops such as maize, soybean and vegetables, site-specific and sensor-driven weed management including machine-vision and deep-learning weed identification, field mapping with UAVs/drones, mechanical weeders using robots and variable or targeted smart-sprayer herbicide application have advanced rapidly, with some machine-vision-guided systems showing a reduction of herbicide use by 4851% and detection accuracy of > 98% in controlled trials (Fig 5).


       
However, the accuracy of field-condition testing is considerably lower than that of indoor or trial-plot testing and published and validated applications are less numerous than those for maize, soybean and vegetable crops, especially for Indian crops. This is not yet a practice, but an explicit knowledge gap (Section 13).
       
Pulse-specific challenges (narrow row spacing for some crops, low crop/weed seedling canopy contrast in early growth stages and smallholder-scale economics in much of the Indian legume-growing area) will require dedicated validation before these technologies can be responsibly recommended to legume growers.
 
Emerging herbicide-tolerant legume cultivars
 
Herbicide-tolerant (HT) cultivars provide a genetic pathway to overcome the limited post-emergence herbicide options outlined in Section 5.3, in addition to new herbicide chemistry. Legumes are among  the most advanced crop in terms of tolerance to AHAS-inhibiting (acetohydroxyacid synthase, also known as ALS) herbicides, which are marketed under the Clearfield® technology platform first developed for cereals and canola and then applied to legume breeding programmes.
       
Considerable variability in imazethapyr and metribuzin tolerance has been observed in large collections of chickpea germplasm and this variability has been used as the basis for marker-assisted introgression of imazethapyr and metribuzin tolerance into elite chickpea germplasm; Australian and Canadian breeding programmes have introgressed imidazolinone-tolerant chickpea and lentil lines into elite germplasm, enabling the use of broad-spectrum AHAS-inhibiting herbicides in-crop without unacceptable injury.
       
Herbicide-tolerant lentils are at a similar stage of development as herbicide-tolerant chickpeas, with imidazolinone-tolerant cultivars released or near release and adopted in parts of Australia and Canada to control broadleaf and grass weed complexes where conventional pre-emergence chemistry is not effective.
       
The current state of breeding in most legume crops is at an earlier stage than in canola, soybean, or maize, where herbicide-tolerant traits are now the agronomic standard in some producing nations. Adoption is currently focused on grain legumes, with herbicide-tolerant chickpea and lentil available in Australia and Canada, respectively and a breeding pipeline gap for herbicide-tolerant pigeonpea, mungbean, urdbean and field pea, where there are limited post-emergence herbicides listed in Table 2.
       
The use of herbicide-tolerant cultivars also has a direct interaction with the resistance management concerns raised in Section 6: widening the in-crop herbicide toolkit through genetics, rather than relying on a small number of repeatedly used modes of action, is one of the more durable near-term strategies available for slowing resistance selection in legume-associated weed populations, provided the trait itself is deployed alongside mode-of-action rotation rather than as a single-herbicide programme.
 
Economics of weed management practices
 
Weed-control economics in legumes depend on the interaction between the yield response, direct cost of weed control and the opportunity cost of labour at the time of weed control and are best expressed as a net return and benefit-cost (B:C) ratio rather than yield alone.
       
In an Indian mungbean trial, weed-free maintenance resulted in the highest grain yield, while a post-emergence fenoxaprop-p-ethyl plus chlorimuron-ethyl programme produced the highest B:C ratio of all treatments tested, including hand weeding and weed-free maintenance, when labour costs were considered in the net return. This finding-that chemical or integrated programmes can provide higher economic returns than full hand weeding when agronomic performance is comparable-is consistent with findings across the international literature.
       
Labour saving is a significant part of this calculation: an integrated programme that replaces two or three weedings with one at the CPWC window can cut labour requirements by about 50%, which becomes a critical factor when local labour rates surpass the cost of an equivalent herbicide treatment, as is increasingly becoming the case in much of rural India and in mechanised production systems in Australia, Canada, Brazil and the United States.
       
There is also an economic aspect to resistance management: a programme of herbicides with different modes of action, whether sequential or tank-mixed, will generally cost more per hectare than a single herbicide programme, but may become the only economically sensible option once resistance has become established, as a failed single herbicide application will result in a total loss of the herbicide cost and yield and a significant impact on net return and benefit-cost (B:C) ratio.
       
Table 3 collates the key weed issues highlighted in this review with the solutions that are currently available, the practical constraints on these solutions and the future opportunities and provides a qualitative research-priority rating, to enable readers to easily identify practical implications.


 
Knowledge gaps
 
The reported gaps span data availability, technology validation and mechanistic understanding.
• However, CPWC data are not available for many legume-growing regions and for many crops or cultivars and are often based on a few published trials, which limits the accuracy of spray-timing recommendations for regions.
• Broadleaf-active post-emergence herbicide options for rabi legume crops (chickpea, lentil and field pea) remain limited relative to kharif legume crops, with topramezone being a promising but still narrowly validated exception.
• Nodulation and BNF impact have been systematically screened for only a small number of herbicide-legume combinations (pendimethalin, clethodim, glyphosate and a handful of others) relative to the full set of compounds in field use.
• Herbicide resistance monitoring specific to legume-associated weed populations is sparse relative to the extensive surveillance literature for wheat, rice, maize and cotton systems, despite shared weed flora and shared ALS-inhibitor chemistry across cereal-legume rotations.
• Bioherbicide field trials in grain legumes (as opposed to maize, vegetables, or organic bean/corn systems) are limited; most current evidence is extrapolated from other crop systems.
• Climate-change interaction studies involving elevated CO‚/temperature, herbicide efficacy and nodulation exist for very few legume species-groundnut being a rare, recent Indian exception-and are essentially absent for chickpea, pigeonpea, mungbean, urdbean and lentil.
• Precision agriculture and AI-based weed-detection systems remain largely unvalidated under actual legume crop field conditions and in smallholder economics.
• Long-term, multi-location performance data for IWM packages that combine reduced herbicide dose with increased seeding density-an approach showing promise in organic systems abroad-are lacking under Indian legume cropping intensities.

Based on the above gaps in knowledge, the following research directions are proposed: breeding for early crop vigour and inherent weed competitiveness; targeted development and dose standardisation of broadleaf-active post-emergence herbicides for rabi legume crops; systematic nodulation/BNF screening to be expanded to the entire spectrum of herbicides in use in the field, not just the few already tested; resistance-monitoring networks specific to legume-associated weed populations, integrated with existing cereal-system monitoring; and accelerated breeding of herbicide-tolerant cultivars beyond the existing chickpea and lentil cultivars.
       
Additional priorities include field-scale validation of allelopathic residue and bioherbicide methods, particularly in grain legumes; multi-environment precision weed identification and variable-rate spraying technologies in smallholder and mechanised production conditions, as well as stepwise, economically feasible validation of CPWC and herbicide-efficacy experiments particularly designed to capture climate variability rather than a single growing season.
       
Future research should focus on climate-resilient weed management, monitoring of herbicide resistance, AI-assisted weed detection, herbicide-safe rhizobial interactions and integrated weed management strategies to sustain legume productivity under changing climates.

This review draws four clear, actionable messages from the Indian and international evidence.
       
First, integrated weed management (IWM), which is a combination of cultural practices, a pre-emergence herbicide appropriate for the legume establishment stage and timely hand weeding or a compatible post-emergence herbicide targeted to the CPWC, is the most sustainable and widely applicable method for controlling weeds in legumes, rather than relying on any single approach.
       
Second, herbicide resistance is a global, not regional, problem in legume crop weed management and requires diversified, mode-of-action-rotated approaches that are applied throughout the entire crop rotation period.The ALS-resistance issues in Echinochloa spp. and Trianthema spp. in India, multi-resistant Palmer amaranth in North America and glyphosate-resistant Conyza in Brazil are all examples of this.
       
Third, the field-level research on bioherbicides and other eco-friendly methods should be significantly increased in grain legumes, because of their potential to reduce selection pressure for herbicides resistance development and their compatibility with nodulation/BNF concerns specific to this crop group.
       
Fourth, climate change is not a far-off prospect but a variable that has already been demonstrated to affect herbicide efficacy and nodulation in at least one Indian legume system (groundnut) and will increasingly be a real factor in the response as precision-agriculture and AI-based tools become more validated for legumes. Closing the identified nodulation-impact and climate-interaction data gaps would significantly improve the accuracy and longevity of weed-management recommendations for legume producers worldwide.

The authors gratefully acknowledge the contributions of all co-authors to literature collection, critical analysis, information synthesis and manuscript preparation.
 
Disclaimers
 
The views expressed in this article are solely those of the authors. Although every effort has been made to ensure the accuracy of the information, the authors accept no responsibility for any loss or consequences resulting from its use.
 
Informed consent
 
Not applicable. This is a review article that does not involve primary animal or human experimental work.

The authors declare no conflict of interest.