Bio-efficacy and economics of pre- and post-emergence herbicides in Barley (Hordeum vulgare L.)

Introduction

Barley (Hordeum vulgare L.) ranks fourth among cereals globally after wheat, rice and maize, and is an important rabi crop in India valued for its adaptability to marginal and saline environments and its role in the malting and brewing industries. Its high dietary fibre content, particularly betaglucans (17-30%), is beneficial for cholesterol and blood-glucose management, leading to its recognition as a functional food. In the Mullana (Ambala) region of Haryana, barley productivity is severely constrained by a complex weed flora comprising grassy weeds such as Phalaris minor and Cynodon dactylon, and broadleaf weeds including Chenopodium album, Melilotus alba and Anagallis arvensis, which compete with the slow-establishing crop for moisture, light and nitrogen. Yield losses of 40-78% have been reported where weeds are left unmanaged during the critical period of crop-weed competition (25-60 DAS) (Tanveer et al. 2012) [9] . Manual weeding, though effective, is becoming economically unviable owing to rising labour costs and scarcity, and is further complicated by weeds such as P. minor that morphologically mimic barley at early growth stages. Herbicides such as pyroxasulfone, sulfosulfuron and metsulfuron-methyl, applied alone, in sequence, or as tankmixes, have shown promise for broad-spectrum control in wheat and barley (Punia et al. 2017, Pal and Singh 2021) [7, 6] , but their comparative performance under local conditions required evaluation. Against this background, the present investigation was planned to assess how pre-and post-emergence herbicide treatments affect the growth and yield of barley, to gauge their efficacy against the local weed spectrum, and to determine the most economical option based on the benefit:cost ratio.

Materials and Methods

The field trial was conducted at the Agricultural Research Farm, Faculty of Agriculture, Maharishi Markandeshwar (Deemed to be University), Mullana-Ambala, Haryana, situated at 30° 15' N latitude and 77° 02' E longitude at an elevation of 274 m, during rabi 2022-23; the location has a semi-arid, sub-tropical climate. The experimental soil was sandy loam in texture and mildly alkaline in reaction (pH 7.9), with low organic carbon (0.42%) and available nitrogen (185 kg/ha), and moderate levels of available phosphorus (14.5 kg/ha) and potassium (210 kg/ha). A randomized block design with eight treatments and three replications was adopted, using a gross plot of 4 m × 4 m and a net plot of 3.68 m × 3.68 m. Barley cv. 'BH 946' was sown during the first fortnight of November at a seed rate of 80 kg/ha with 22.5 cm row spacing, and received 60-13-17 kg N-P-K/ha, of which half the nitrogen along with the full dose of phosphorus and potassium was applied as basal, the remaining nitrogen being topdressed at the first irrigation. Eight treatments were imposed: T 1 , pyroxasulfone at 130 g/ha (pre-emergence); T 2 , sulfosulfuron at 30 g/ha (post-emergence); T 3 , pyroxasulfone (130 g/ha) followed by sulfosulfuron (30 g/ha); T 4 , a post-emergence tank-mix of sulfosulfuron (30 g/ha) followed by metsulfuron-methyl (3 g/ha); T 5 , metribuzin at 210 g/ha (post-emergence); T 6 , metsulfuronmethyl at 3 g/ha (post-emergence); T 7 , two hand weedings carried out at 20 and 40 DAS; and T 8 , an untreated weedy check. Preemergence sprays were applied within 0-3 DAS and postemergence sprays at 30-35 DAS, using a knapsack sprayer fitted with a flat-fan nozzle set to deliver a spray volume of 500 litres of water/ha. At 30, 60 and 90 DAS, weed density and dry weight were assessed using a 0.25 m² quadrat placed at two randomly chosen spots per plot; count data were square-root transformed (√x+0.5) prior to analysis of variance, though the untransformed means are presented here. Weed control efficiency was derived from the relationship WCE (%) = [(WDC -WDT)/WDC] × 100, where WDC and WDT represent weed dry weight in the untreated weedy check and the herbicide-treated plot, respectively. Plant stand was counted at 21 DAS, while plant height, tiller number and dry matter accumulation were tracked at successive stages of crop growth; spikes/m², grains per spike, test weight, grain yield, straw yield, biological yield and harvest index were determined at crop maturity from the net plot area. All data were subjected to analysis of variance appropriate to a randomized block design following the procedure of Gomez and Gomez (1984) [3] , with treatment means compared using the critical difference at the 5% probability level. Economic indices, namely cost of cultivation, gross returns, net returns and the benefit:cost (B:C) ratio, were derived using prevailing input costs and market prices of produce.

Results and Discussion

Crop growth

Plant population at 21 DAS was unaffected by herbicide treatment (79.5-81.3/m²; Table 2), confirming a uniform crop stand and the absence of phytotoxic effects of the pre-emergence herbicides pyroxasulfone and metribuzin on barley germination. Significant differences in plant height, tiller number and dry matter accumulation (DMA) emerged from 60 DAS onward. At harvest, T 4 (sulfosulfuron fb metsulfuron-methyl) recorded the tallest plants (98.1 cm), the highest tiller density (255/m²) and the greatest DMA (979.3 g/m²), on par with T 3 (pyroxasulfone fb sulfosulfuron) and T 7 (two hand weedings) but 12-18% higher than the weedy check, which recorded the lowest values for all three parameters. The superior and season-long performance of T 4 and T 3 reflects the value of combining herbicides with complementary timing to suppress both early and late weed flushes, sustaining a larger crop canopy for light interception through the season.

Yield attributes and yield

Spikes/m², grains/spike, test weight, grain yield and harvest index were significantly influenced by weed management (Table 3). T 4 produced the most spikes/m² (246.7), grains/spike (44.0) and highest test weight (41.4 g), on par with T 7 and T 3 , while the weedy check recorded the lowest values for every attribute (196.7 spikes/m², 34.0 grains/spike, 35.3 g test weight). Grain yield followed the same trend, being highest under T 4 (4.44 t/ha) and harvest index (44.2%), followed by T 7 (4.31 t/ha) and T 3 (4.29 t/ha), while the weedy check yielded only 2.29 t/ha-a loss of about 48.4% relative to T 4 , consistent with the yield-loss range reported for uncontrolled weed competition in barley (Tanveer et al. 2012) [9] . The lower harvest index of the weedy check (38.9%) indicates that weed stress impaired grain-filling more severely than vegetative growth. That T 4 matched or exceeded the labourintensive T 7 across most growth and yield attributes demonstrates that a well-timed herbicide programme can substitute for manual weeding without yield penalty.

Economics

Economic returns did not mirror biological performance for all treatments (Table 4). Although T 7 achieved yields comparable to T 4 , its cultivation cost (Rs 52,500/ha) was much higher owing to labour requirement, giving the lowest B:C ratio (1.82) among weed-managed treatments and net returns of only Rs 42,873/ha. T 4 combined high yield with moderate input cost (Rs 33,850/ha), giving the highest net returns (Rs 64,067/ha) and B:C ratio (2.89) of all treatments, about Rs 21,000/ha more profitable than hand weeding. The weedy check, despite the lowest cultivation cost, gave the poorest economics overall (B:C ratio 1.65), showing that omitting weed control results in a net financial loss under prevailing labour costs.

Weed density, weed dry weight and weed control efficiency

Weed density and dry weight increased through the season in all treatments but rose sharply in the weedy check, reaching 30.9/m² and 28.7 g/m² at 90 DAS, about four times higher than under T 4 (Table 5). T 4 gave the most consistent suppression across sampling dates, remaining statistically comparable to T 7 and significantly lower than the solo pre-emergence treatments T 1 and T 5 . Correspondingly, T 4 recorded the highest WCE at every stage, remaining above 50% even at 90 DAS. WCE and grain yield were positively associated across treatments, with T 4 and T 3 recording both the highest WCE and the highest yields, confirming that suppression of weed biomass rather than weed number is the more direct determinant of yield. The consistently superior performance of the sulfosulfuron + metsulfuron-methyl tank-mix reflects the complementary spectrum of the two active ingredients against the mixed grassy and broadleaf flora at the site, corroborating similar reports in wheat and barley (Punia et al. 2017, Pal and Singh 2021) [7, 6] . Season-long weed competition, when left unchecked, cost barley growers roughly 48.4% of their grain yield, driven by the high weed density and biomass that built up by 90 DAS. Among the options tested, the post-emergence tank-mix of sulfosulfuron (30 g/ha) and metsulfuron-methyl (3 g/ha) delivered the best combination of weed suppression, grain yield, net returns and B:C ratio, matching two hand weedings while costing substantially less, and is therefore recommended for barley growers in Haryana and comparable agro-climatic zones. Where growers prefer to include a residual pre-emergence component, pyroxasulfone followed by sulfosulfuron offers a suitable alternative; none of the herbicide treatments produced any visible crop injury. --PE = pre-emergence; POE = post-emergence; DAS = days after sowing; fb = followed by.

References

1. Aadil S, Tomar V. Efficacy of post-emergence herbicides for weed management in winter barley (Hordeum vulgare L.). Indian Journal of Weed Science. 2022;54(2):145-150.
2. Blackshaw RE, Harker KN. Selective post-emergence control of Bromus tectorum in winter wheat with sulfosulfuron. Weed Technology. 2002;16(1):23-31.
3. Gomez KA, Gomez AA. Statistical procedures for agricultural research. 2 nd Ed. New York: John Wiley and Sons; 1984. p. 680.
4. Kaur S, Kaur R, Singh T. Effect of different herbicides on weed control and yield of barley (Hordeum vulgare L.). Journal of Pharmacognosy and Phytochemistry. 2018;7(2):1234-1238.
5. Meena RK, Singh RP. Integrated weed management in barley under irrigated conditions of northern India. Journal of Cereal Research. 2023;15(1):45-52.
6. Pal S, Singh H. Bio-efficacy of sulfosulfuron and metsulfuron-methyl against complex weed flora in wheat and barley. Indian Journal of Agronomy. 2021;66(3):289-294.
7. Punia SS, Hooda VS, Yadav DB. Bio-efficacy of sulfosulfuron + metsulfuron-methyl against complex weed flora in wheat. Journal of Wheat Research. 2017;9(2):121125.
8. Saini JP, Angiras NN. Evaluation of new herbicides for the control of Phalaris minor in barley. Himachal Journal of Agricultural Research. 2019;45(1):12-18.
9. Tanveer A, Sibtain M, Javaid MM. Influence of weed-crop competition period on yield and yield components of barley. Pakistan Journal of Weed Science Research. 2012;18(4):459469.
10. Yadav DB, Yadav A, Punia SS. Evaluation of pyroxasulfone against Phalaris minor in wheat. Indian Journal of Weed Science. 2009;41(3-4):150-153.