Efficacy of certain new generation herbicides in blackgram (Vigna mungo L.)

Introduction

Pulses are among the most superior and important groups of crops to provide plant protein of the highest quality. Their proteins complement cereal proteins in the largely vegetarian Indian diet. The pulses play an important role in nutritional security, especially in populations that are dependent upon vegetarian food sources. With respect to agriculture, pulses enrich the soil and thus help in eco-friendly farming (Saravanane et al. 2020) [1] . Among various pulse crops, blackgram (Vigna mungo L.), popularly called urdbean, uradbean, mashbean, minapapappu, mungobean, or black mapte bean, has a place in prominence due to its wide adaptability, short growth duration, and high nutritional value (Nihal et al. 2025) [2] . It finds wide cultivation in all tropical and subtropical regions of the world, especially in India; obviously, for it grows under the various agro-ecological conditions. Blackgram may be cultivated as a pure crop, mixed crop, catch crop, or even as a sequential crop, especially under residual soil moisture after the harvesting of rice. The adaptability of blackgram has become an advantage for it to be grown in both kharif and rabi seasons, providing sustenance to small and marginal farmers. Nutritionally, blackgram is an excellent source of carbohydrates (48%), protein, iron (9.1 mg), fat (1.4 g), riboflavin (0.37 g), and thiamine (0.42 mg) per 100 g of seed (Asaduzzaman et al. 2010) [3] . It is unique among pulses due to its ability to form a mucilaginous, pasty texture upon soaking, which makes it an essential ingredient in many traditional Indian foods such as vada, idli, dosa, and halwa. Additionally, blackgram residues (bhusa) serve as valuable livestock feed, improving nitrogen, calcium, and phosphorus balance in animals. Weed infestation is a major biotic stress that adversely affects the growth and productivity of blackgram. The short-statured and compact varieties currently under cultivation, such as TBG 104 and PU-31, are high-yielding and diseaseresistant, but they exhibit slow early growth, making them less competitive with weeds. Moreover, weeds act as alternate hosts for insect pests and viruses, including the Yellow Mosaic Virus, exacerbating crop damage (Dhayal et al. 2022) [4] . The critical period of crop-weed competition in blackgram occurs between 15 to 45 days after sowing (DAS). Yield losses due to weed competition can range from 50% to 87%, depending on the weed species composition and density. Traditional weed management methods such as hand weeding and intercultivation are increasingly uneconomical due to the rising cost and scarcity of agricultural labor. Additionally, continuous rainfall during the early crop stages often disrupts timely manual weeding operations. In recent years, the use of herbicides in pulse-based cropping systems has gained considerable importance as an effective and economical method for weed control. However, over reliance on selective post-emergence herbicides, particularly those targeting grassy weeds, has led to weed flora shifts toward broadleaf species. A notable example is the increasing prevalence of common vetch (Vicia sativa L.), which has become a problematic weed in blackgram relay cropping systems, especially in the north coastal zone of Andhra Pradesh (Malviya and Saini, 2023) [6] . While pre-emergence herbicides such as pendimethalin have been widely adopted, they are often ineffective against perennial sedges like Cyperus rotundus and certain broadleaf weeds such as Commelina benghalensis and Trichodesma indicum. Similarly, post-emergence application of imazethapyr alone fails to provide broad-spectrum weed control due to the diversity of weed flora in blackgram fields. Recent research suggests that new-generation herbicides and ready-mix formulations, such as combinations of imazethapyr with pendimethalin or propaquizafop, show promising results for controlling both grassy and broadleaf weeds effectively. These formulations also offer extended residual activity, reduce labor dependency, and promote better crop establishment and yield performance.

Materials and Methods

The present experiment is laid out in the field of the Research Farm of Department of Agronomy, Sardar Patel University Balaghat-481331, M.P. during kharif season, 2024-25. The land topography of the experimental site was almost uniform with an adequate surface drainage. The internal drainage of the experimental site is medium. The field experiment was laid out in a Randomized Block Design (RBD) with three replications to statistically evaluate the treatment effects. The experimental field was heavily infested with a diverse assemblage of weed species representing all major groups grasses, sedges, and broad-leaved weeds typical of the rainfed tropical ecosystem. The grassy weeds were dominated by Digitaria sanguinalis (large crabgrass), Cynodon dactylon (Bermuda grass), and Echinochloa colona (jungle rice), which are known for their rapid germination, profuse tillering, and strong competitive ability for soil nutrients, moisture, and sunlight. These species, particularly Cynodon dactylon, possess vigorous underground rhizomes that enable them to regenerate even after mechanical disturbance, making them among the most persistent perennial weeds in pulse-growing regions (Tripathi & Pandey, 2020) [7] . The sedge component was represented mainly by Cyperus rotundus (purple nut sedge), a notorious perennial weed with a prolific underground tuber system. Its ability to survive adverse conditions and multiply rapidly even under limited moisture makes it a constant menace in kharif pulses. [2,9,10] . In this context, the use of herbicides with residual and broad-spectrum activity becomes essential to restrict early weed establishment. Diclosulam, when applied as a preemergence treatment, exhibited strong residual soil activity and effectively prevented the germination and establishment of both monocot and dicot weeds. Its mode of action involves inhibition of acetolactate synthase (ALS) enzyme, which is vital for the synthesis of branched-chain amino acids in weeds. The selectivity of diclosulam to blackgram ensured that the crop remained unaffected while the emerging weeds were completely suppressed. Pendimethalin + imazethapyr, another pre-emergence combination, offered broad-spectrum control by inhibiting both shoot and root growth in emerging weeds. However, its residual effect was relatively shorter than that of diclosulam, resulting in a mild re-emergence of weeds at later stages (Marimuthu et al. 2024; Singh et al. 2018) [8,12] . [5,13,16] . Weed density and dry matter are direct indicators of treatment efficacy. The data showed that all herbicidal treatments significantly reduced weed density compared with the unweeded control. Diclosulam completely suppressed weed emergence up to fifteen days after sowing, maintaining a weed-free condition during the most sensitive phase of the crop. Pendimethalin + imazethapyr also performed well but allowed a slight infestation of sedges and broad-leaved weeds. Post-emergence herbicides reduced existing weeds but were less effective in preventing later germination. As the crop advanced, weed density increased in all treatments, yet plots receiving a combination of herbicide and hand weeding at thirty days remained the cleanest. The unweeded control, on the other hand, maintained a consistently high population, confirming that continuous interference from weeds limits crop growth severely (Marimuthu et al. 2024; Singh et al. 2018) [8,12] . Weed dry matter followed the same trend as density. The minimum weed biomass at all growth stages occurred in diclosulam + hand-weeding plots, followed closely by pendimethalin + imazethapyr + hand and two handweeding treatments. The integrated use of chemical and manual control ensured both residual suppression and removal of late-emerging weeds, resulting in sustained low biomass even at harvest. Conversely, unchecked weed growth in the control plots produced heavy dry matter accumulation, which competed with the crop for nutrients, light, and moisture. The superiority of integrated methods over chemical-only options clearly demonstrated the advantage of combining persistence with mechanical removal to achieve season-long control (Marimuthu et al. 2024; Singh et al. 2018) [5,12] . Weed control efficiency exhibited a clear inverse relationship with weed biomass accumulation, indicating that treatments capable of maintaining lower weed dry matter were also those with higher control efficiency. Among the various treatments tested, the maximum efficiency values were obtained in plots treated with diclosulam followed by hand weeding, pendimethalin + imazethapyr combined with hand weeding, and the treatment involving two manual weedings (Mishra & Yaduraju, 2017; Jadhav & Bhattacharya, 2019) [14,15] . These treatments were successful in keeping the field nearly free from weed competition throughout the crop growth period, which was reflected in their consistently high WCE values exceeding 70 percent even at harvest. Diclosulam, when applied as a pre-emergence herbicide, provided almost complete control during the early phase of the crop, maintaining near-total efficiency up to fifteen days after sowing. However, as its residual activity gradually declined with time and successive rainfall events, a small proportion of late-emerging weeds managed to establish, leading to a slight reduction in efficiency at later stages (Marimuthu et al. 2024; Singh et al. 2018) [8,12] . Incorporation of a single hand-weeding operation at thirty days after sowing effectively complemented the herbicide's residual action by physically removing surviving and newly emerged weeds. This integration not only revived the weed control efficiency but also sustained it at a higher level beyond sixty days, ensuring prolonged suppression until harvest. The combination of chemical and manual interventions thus demonstrated the advantage of sequential management, where herbicide application prevents early weed establishment while mechanical weeding eliminates later flushes that escape chemical control (Mishra & Yaduraju, 2017; Jadhav & Bhattacharya, 2019) [14,15] . On the other hand, post-emergence herbicides such as propaquizafop + imazethapyr and sodium acifluorfen + clodinafop recorded only moderate weed control efficiency. Their lower performance was mainly due to their foliar mode of action, which targets actively growing weeds present at the time of application but provides little or no residual effect on subsequently emerging species. Moreover, the presence of perennial weeds like Cyperus rotundus and Cynodon dactylon, which can regenerate from underground structures, further reduced the long-term effectiveness of post-emergence treatments. Consequently, weed biomass in these plots tended to increase at later growth stages, leading to a decline in overall efficiency (Singh et al. 2018; Patel & Patel, 2022) [5,13,16] . The progressive reduction in WCE across all treatments with advancing crop age highlights the dynamic nature of weed emergence and the limitations of single-stage interventions. Continuous or staged weed management is essential to counter repeated germination waves under tropical kharif conditions where soil moisture fluctuations favour multiple weed flushes. Treatments that combined pre-emergence herbicides with a manual operation or mechanical weeding were able to maintain superior efficiency over time because they integrated both preventive and curative measures. Maintaining weed control efficiency above seventy percent until harvest proved critical for minimizing competition, conserving soil resources, and achieving higher yield. The results clearly demonstrate that an integrated approach, rather than reliance on any single herbicide, is necessary for sustaining long-term weed suppression and ensuring optimum productivity of blackgram (Mishra & Yaduraju, 2017; Jadhav & Bhattacharya, 2019) [14,15] . Observations on crop safety revealed that all the herbicides evaluated in the experiment were highly selective and safe for blackgram at the recommended rates of application. No major phytotoxic symptoms were observed in any treatment, indicating that the tested herbicides were compatible with the crop's physiological and biochemical systems. Diclosulam, when applied as a pre-emergence herbicide, caused only a mild and transient yellowing of cotyledons and the first true leaves during the initial few days after application. This temporary chlorosis was attributed to slight physiological stress induced by the herbicide's residual presence in the topsoil; however, the symptoms completely disappeared within a week as the crop resumed normal growth. The rapid recovery of plants indicated that diclosulam, though biologically active in soil for a considerable period, remains selective to blackgram due to its limited uptake and efficient metabolic detoxification within plant tissues. Furthermore, no adverse effect on germination, plant stand, or seedling vigour was observed, confirming the crop's tolerance to its recommended dose (Marimuthu et al. 2024; Singh et al. 2018) [5,12] . The herbicide combinations involving pendimethalin + imazethapyr, propaquizafop + imazethapyr, and sodium acifluorfen + clodinafop exhibited excellent crop safety throughout the growing period. [5,13,16] . Overall, the absence of any significant or lasting phytotoxic effects across treatments confirmed the compatibility of all the tested herbicides with blackgram and demonstrated that the crop can safely tolerate their recommended doses under field conditions. The selectivity of these herbicides ensures that they can be effectively incorporated into integrated weed management programmes without the risk of crop injury or stand reduction. This aspect is particularly important for pulse crops like blackgram, which are generally sensitive to chemical stress during early growth stages. The results therefore validate the suitability of these herbicides for practical field use and reinforce the importance of dose accuracy and proper timing to maintain both crop safety and weed control efficacy (Mishra & Yaduraju, 2017; Jadhav & Bhattacharya, 2019) [14,15] . The uniformity of plant population across treatments showed that none of the herbicides interfered with germination or establishment. Differences in plant height, however, were pronounced. [5,12] . Leaf area index exhibited a similar pattern. Higher LAI in effectively weed-controlled plots indicated increased photosynthetic surface and enhanced light interception, while lower values in weedy plots resulted from shading by competing weeds. The number of branches per plant was also higher in weed-free conditions, reflecting improved physiological activity and nutrient availability. Under heavy weed pressure, the crop produced fewer branches due to suppressed growth and reduced assimilate supply (Marimuthu et al. 2024; Singh et al. 2018) [5,12] . Dry matter accumulation in the crop canopy followed an increasing trend until harvest and was significantly influenced by weed control. [5,12] . Yield attributes such as number of pods per plant, seeds per pod, and test weight reflected the cumulative effect of weed management on crop growth. The maximum pods per plant were obtained in pendimethalin + imazethapyr + handweeding, closely followed by diclosulam + hand-weeding and two hand-weedings. The increase in pod number under these treatments resulted from improved branching, better flowering, and reduced abortion of reproductive structures due to absence of stress. Seeds per pod also increased under effective weed control because plants grown under weedfree conditions could allocate more assimilates for seed development (Marimuthu et al. 2024; Singh et al. 2018) [5,12] . Similarly, test weight improved considerably when weeds were effectively managed, suggesting that nutrients and photosynthates were efficiently partitioned to the seeds (Sinha & Prakash, 2019; Patel & Patel, 2022) [13,16] . The final seed and haulm yields mirrored the trends in yield attributes. Pendimethalin + imazethapyr + hand-weeding produced the highest seed yield, followed by two handweedings and diclosulam + hand-weeding. The yield advantage over the unweeded control exceeded sixty percent, confirming the severe yield loss caused by weed competition in blackgram. Higher haulm yield in these treatments indicated overall improvement in biomass production and better growth vigour. The harvest index was also greater in effectively weed-controlled plots, reflecting a higher proportion of economic yield to total biomass. In contrast, the unweeded control recorded a lower harvest index due to poor partitioning efficiency. The weed index, which denotes yield reduction relative to the best treatment, was lowest in the integrated treatments, further confirming their superiority in maintaining yield potential (Marimuthu et al. 2024; Singh et al. 2018) [5,12] .

Conclusion

The results of this investigation lead to the following major conclusions 1. The experimental field was infested with a complex weed flora comprising annual and perennial grasses, sedges, and broad-leaved weeds. Effective control of these species was essential during the early growth stages of blackgram to minimize yield loss. 2. Pre-emergence application of diclosulam 20 g ha⁻¹, followed by one hand-weeding at 30 DAS, proved to be the most efficient treatment in suppressing weeds, reducing their biomass, and maintaining high weed control efficiency throughout the crop growth period. 3. The treatment pendimethalin + imazethapyr @ 1000 g ha⁻¹ + hand-weeding was equally effective and statistically comparable to diclosulam + hand-weeding in most parameters. 4. Post-emergence herbicides such as propaquizafop + imazethapyr and sodium acifluorfen + clodinafop provided moderate control of existing weeds but were less effective in preventing later flushes due to lack of residual activity. 5. All herbicides were found safe and selective to blackgram, showing no adverse effect on crop stand, nodulation, or growth. 6. Effective weed control significantly improved all growth and yield attributes, leading to higher seed and haulm yields. 7. In terms of economic efficiency, diclosulam + handweeding at 30 DAS recorded the highest net returns and benefit-cost ratio, making it the most profitable option under the prevailing conditions. 8. Therefore, integrated weed management involving a pre-emergence application of diclosulam followed by one timely hand-weeding is recommended as the most suitable, cost-effective, and environmentally sustainable weed control strategy for blackgram cultivation in similar agro-climatic regions.

In conclusion, the study emphasizes that early-season integrated weed management is the key to achieving high productivity and profitability in blackgram. Adoption of such practices will not only enhance yield but also contribute to sustainable pulse production by reducing herbicide load, conserving soil health, and maintaining ecological balance in the farming system.

References

1. https://www.biochemjournal.com Treatments Dry matter production (kg ha⁻¹) 15 DAS 30 DAS 45 DAS 60 DAS At harvest W₁: Pre-emergence (PE) application of diclosulam 20 g ha⁻¹ 157 388 702 1118 1741 W₂: PE application of pendimethalin + imazethapyr 1000 g ha⁻¹ 201 407 714 1180 1926 W₃: PE application of diclosulam 20 g ha⁻¹ + Hand weeding (HW) at 30 DAS 159 393 717 1217 2080 W₄: PE application of pendimethalin + imazethapyr 1000 g ha⁻¹ + HW at 30 DAS 204 414 721 1304 2093 W₅: Post-emergence application of propaquizafop + imazethapyr 127 g ha⁻¹ at 15 DAS 189 392 691 1088 1714 W₆: Post-emergence application of sodium acifluorfen + clodinafop propargyl 180 g ha⁻¹ at 15 DAS 188 384 677 1041 1668 W₇: PE application of pendimethalin 1000 g ha⁻¹ 195 401 684 1129 1752 W₈: Post-emergence application of imazethapyr 75 g ha⁻¹ at 15 DAS 189 375 672 1009 1653 W₉: Two hand weedings at 15 and 30 DAS 187 412 721 1264 2084 W₁₀: Unweeded check (Control) 186 372 627 911 1180 SE± 5.90
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