Weed management studies in transplanted rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) belonging to the Poaceae family, is a vital cereal grain, especially in East and Southeast Asia, where it serves as a staple food for nearly half of the world's population. It plays a significant role in human diets, with 95% of global rice production consumed directly by people. Rice is rich in starch and contains 6-7% protein, known as oryzein and about 2.5% fat. Beyond direct consumption, it is also used in the production of alcoholic beverages, starch and rice flour. Globally, rice provides approximately 20% of dietary energy, while wheat and maize contributing 19% and 5%, respectively (Mamun et al., 2011) [13] . For undernourished populations in Asia and Africa, rice is often the most accessible and affordable food, making it indispensable for food security. As a strategic commodity, rice not only addresses global nutritional needs but also has broad implications for economic growth, employment, social stability and peace, particularly in regions where it is a dietary mainstay. Rice is the most important staple food for more than half of the world population. The warm and humid climatic conditions are prevailing in most part of Asia is well suited to rice production. It is grown in India on 46.38 M ha area and 130.29 Million tonnes production with national average yield 2.809 t ha -1 during the year 2021-22 and in Chhattisgarh, rice is cultivated in 3.76 M ha area and production is 7.90 Mt with average yield 2.101 t ha -1 (Anonymous, 2022-23) [2] . With a growing population, India will need to produce more rice to meet rising demand, which is reach expected to 130 million tonnes by 2030. Effective weed management is essential in transplanted rice, especially during the critical period of competition, to achieve optimal yields. This period, when weeds can severely impact rice development by competing for resources, requires targeted intervention. Controlling weeds during this time is crucial to maximize rice productivity and ensure that crops can grow with minimal interference from competing vegetation (Khaliq et al., 2011) [10] . Weeds are a major concern in rice cultivation, capable of reducing yields by 50 to 90% due to their intense competition for water, sunlight and nutrients, and by acting as hosts for pests and diseases. While, chemical weed control through herbicides is currently the most common approach, challenges are emerging, including shifts in weed flora, the development of multi-herbicide resistance and environmental pollution. These issues underscore the need for sustainable alternatives to weed management that are less reliant on chemical inputs. Historically, since the advent of agriculture, farmers have faced ongoing struggles with weeds, which can significantly impact crop productivity. Although herbicides have provided a convenient solution for weed control, the consequences of their extensive use suggest a pressing need to integrate more sustainable practices, such as crop rotation, mechanical weeding, mulching and the use of cover crops to reduce reliance on herbicides and promote long-term crop and ecosystem health Chemical weed control through herbicides is one of the most effective and widely employed methods for managing weeds in rice. Hand weeding though efficient, it is expensive, time consuming, difficult task and often limited by scarcity of labour at critical period may lead to unsatisfactory weed control practice. To get rid this hurdle usage of herbicides offer a selective and economical control of weeds right from beginning of crop. Due to continuous usage of same mode of action of herbicides like butachlor, pretilachlor etc. weed shift is observed in transplanted rice. Weed shift from grasses to broad-leaf weeds and sedges were observed in transplanted rice due to continuous use of same herbicides (Teja et al., 2017) [16] . The most problematic and challenging to manage Echinocloa colona in rice field. Due to competition for nutrients, moisture, light and to a lesser extent, space, weeds not only inflict quantitative damage but also lower the quality of produce. The distribution of weeds varies depending on the prevailing meteorological conditions and the quality of the soil. Thus, it is necessary to assess the suitability of new herbicides in the agro-climatic conditions of the Chhattisgarh plain. About 15-20% of the rice crop in Chhattisgarh is transplanted. Due to the drudgery of weeding and the scarcity of labour at the appropriate time, chemical weed control is regarded as a better option than weeding. Preemergence herbicides were previously used for weed management, but their use was limited due to their timely application with adequate soil moisture. As a result, appropriate post-emergence herbicides are required based on the weed flora in transplanted rice.

Materials and methods

A field experiment entitled "Weed management studies in transplanted rice (Oryza sativa L.)" was conducted at Research cum Instructional Farm, Barrister Thakur Chhedilal College of Agriculture and Research Station, Bilaspur (C.G.) during kharif season 2024-25. The experiment was laid out in Randomized Block Design with three replications. The treatments consisted of seven weed management practices viz., (T 1 ) Untreated check, (T 2 ) Weed free, (T 3 ) Hand weeding @ 30 DAT (once), (T 4 ) Fenoxaprop-p-ethyl @ 60 g a.i./ha at 25 DAT, (T 5 ) Bispyribac -Na @ 25 g a.i./ha at 25 DAT, (T 6 ) Fenoxapropp-ethyl @ 60 g a.i./ha at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl 20 g a.i./ha at 25 DAT) and (T 7 ) Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g/L) @ 150 g a.i./ha at 25 DAT. Observations on plant population, plant height, number of tillers and dry matter accumulation were recorded at different time intervals and number of pods, number of panicles, panicle length, number of grains, test weight, grain yield and straw yield of transplanted rice crop were recorded at harvest and statistically analyzed. The total weed density and total production of dry matter by weeds were recorded at 30, 60, 90 DAT and at harvest and statistically analyzed. The crop growth rate, relative growth rate, harvest index, weed index, weed density, weed control efficiency and economics of rice as a cost of cultivation, net return, gross return and benefit: cost ratio were also worked out.

Results and discussions

Crop parameters 1. Plant height at 30, 60, 90 DAT and at harvest revealed significant differences among the treatments. At 30 DAT, significantly taller plants were recorded under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (once). Among herbicidal treatments, T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxapropp-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuronethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT) recorded higher plant height than T₄ -Fenoxaprop-pethyl @ 60 g a.i. ha⁻¹ at 25 DAT and T₅ -Bispyribac-Na @ 25 g a.i. ha⁻¹ at 25 DAT, while the lowest was observed in T₁ -Untreated check. At 60, 90 DAT and at harvest, significantly taller plants were recorded under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), whereas T₁ -Untreated check consistently recorded the lowest plant height. 2. Number of tillers hill⁻¹ at 30, 60, 90 DAT and at harvest showed significant variation among treatments. At 30 DAT, higher tillering was recorded under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), while T₁ -Untreated check recorded the minimum. At 60, 90 DAT and at harvest, T₂ -Weed free recorded the highest number of tillers hill⁻¹, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxapropp-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuronethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), whereas T₁ -Untreated check consistently recorded the lowest tillering. 3. Dry matter accumulation per plant at 30 DAT was highest under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), while T₁ -Untreated check recorded the lowest value. At 60, 90 DAT and at harvest, T₂ -Weed free recorded the highest dry matter accumulation, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), whereas T₁ -Untreated check recorded the lowest dry matter accumulation. 4. Yield attributes such as number of panicles hill⁻¹, panicle length, number of grains panicle⁻¹ and test weight were maximum under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (once), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25 + 125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT and T₆ -Fenoxapropp-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuronethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT), whereas comparatively lower values were recorded under T₄ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT and T₅ -Bispyribac-Na @ 25 g a.i. ha⁻¹ at 25 DAT, and minimum values were observed in T₁ -Untreated check. 5. Grain and straw yield of transplanted rice were maximum under T₂ -Weed free (49.85 and 58.32 q ha⁻¹), followed by T₃ -Hand weeding @ 30 DAT (once) (42.86 and 53.43 q ha⁻¹), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25 + 125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT (40.18 and 50.44 q ha⁻¹) and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT) (39.22 and 49.28 q ha⁻¹), whereas comparatively lower yields were recorded under T₄ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT and T₅ -Bispyribac-Na @ 25 g a.i. ha⁻¹ at 25 DAT, and the minimum grain and straw yield were recorded in T₁ -Untreated check (21.35 and 31.29 q ha⁻¹). 6. Harvest index of transplanted rice was not significantly influenced by treatments; however, numerically higher harvest index was recorded under T₂ -Weed free (46.08%), followed by T₃ -Hand weeding @ 30 DAT (once) (44.51%), T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT (44.34-44.49%) and T₆ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT) (44.32-44.44%), whereas lower values were recorded under T₄ -Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT (43.86%) and T₅ -Bispyribac-Na @ 25 g a.i. ha⁻¹ at 25 DAT (43.48%), and the minimum harvest index was observed in T₁ -Untreated check (40.56%).

Weed parameters

1. Total weed density (sedges, grasses and broad-leaved weeds) was recorded at 30, 60, 90 DAT and at harvest. At 30 DAT, the minimum total weed density was observed under weed-free (T₂ -Weed free), which recorded complete suppression of weeds (0.00 m⁻²); however, among the weed control treatments, Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT (T₇ -30.67 m⁻²) recorded the lowest total weed density, followed by Fenoxaprop-p-ethyl @ 60 g a.i. ha⁻¹ at 25 DAT + Chlorimuron-ethyl + Metsulfuron methyl @ 20 g a.i. ha⁻¹ at 25 DAT (T₆ -31.85 m⁻²) and Hand weeding @ 30 DAT (T₃ -52.38 m⁻²). At 60 DAT, significantly lowest total weed density was recorded under weed-free (T₂ -0.00 m⁻²), while among the treatments, Hand weeding @ 30 DAT (T₃ -10.01 m⁻²) recorded the lowest weed density, followed by T₆ (13.84 m⁻²) and T₇ (14.78 m⁻²). At 90 DAT, a similar trend was observed where weed-free (T₂) recorded zero weed density, and among the weed control treatments, Hand weeding @ 30 DAT (T₃ -11.75 m⁻²) recorded the lowest total weed density, followed by T₇ (16.04 m⁻²) and T₆ (17.39 m⁻²), whereas Fenoxaprop-p-ethyl (T₄ -39.25 m⁻²) and Bispyribac sodium (T₅ -35.19 m⁻²) were comparatively less effective. At harvest, weed-free (T₂) maintained complete suppression of weeds (0.00 m⁻²), and among the weed control treatments, Hand weeding @ 30 DAT (T₃ -13.55 m⁻²) recorded the lowest total weed density, followed by T₇ (18.03 m⁻²) and T₆ (18.61 m⁻²), while the maximum total weed density was recorded under untreated check (T₁ -68.64 m⁻²) at all stages of observation. 2. Weed control efficiency (WCE) was recorded at 30, 60, 90 DAT and at harvest. At 30 DAT, the maximum WCE was observed in T₂ -Weed free (100%), followed by Florpyrauxifen benzyl + Cyhalofop butyl (T₇ -42.12%) and Fenoxaprop-p-ethyl + Chlorimuron-ethyl + Metsulfuron methyl (T₆ -39.89%), which were significantly superior to single herbicide applications. The lowest WCE was recorded in T₁ -Untreated check (0%). At 60 DAT, 90 DAT and at harvest, T₂ maintained complete weed suppression (100%). Among weed control treatments, T₃ -Hand weeding @ 30 DAT, T₇ and T₆ consistently recorded higher WCE (up to 80.25%, 74.94% and 72.89%, respectively). Single herbicide treatments T₄ -Fenoxaprop-p-ethyl and T₅ -Bispyribac sodium showed moderate WCE, while T₁ remained ineffective throughout the crop period.

Economics

The highest cost of cultivation (₹ 61,150 ha⁻¹) was recorded under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (₹ 54,350 ha⁻¹), while the minimum cost was noted under the untreated check (T₁). The highest gross return (₹ 1,60,367.45 ha⁻¹) and net return (₹ 99,217.45 ha⁻¹) were obtained under T₂ -Weed free, followed by T₃ -Hand weeding @ 30 DAT (gross return ₹ 1,38,209.36 ha⁻¹ and net return ₹ 83,859.36 ha⁻¹) and T₇ -Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g L⁻¹) @ 150 g a.i. ha⁻¹ at 25 DAT (gross return ₹ 1,23,122.24 ha⁻¹ and net return ₹ 77,112.24 ha⁻¹). The highest benefit: cost ratio (2.68:1) was recorded under T₇ -Florpyrauxifen benzyl + Cyhalofop butyl, followed closely by T₂ -Weed free (2.62:1). However, the minimum gross return, net return and B:C ratio were observed under the untreated check (T₁).

Conclusion

Weed free (T 2 ) have registered higher growth, yield attributes and yield as well as gross and net return followed by Hand weeding @ 30 DAT (once) (T 3 ), among the chemical weed control Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g/L) @ 150 g a.i./ha at 25 DAT (T 7 ) have recorded higher growth, yield attributes and yield of transplanted rice as compared to other weed management practices. However, the benefit: cost ratio was higher under Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g/L) @ 150 g a.i./ha at 25 DAT (T 7 ). Hand weeding @ 30 DAT (once) (T 3 ) were best performing treatment to control weed growth, among the chemical weed management Florpyrauxifen benzyl + Cyhalofop butyl (25+125 g/L) @ 150 g a.i./ha at 25 DAT (T 7 ) and Fenoxaprop-p-ethyl @ 60 g a.i./ha at 25 DAT + (Chlorimuron-ethyl + Metsulfuron methyl 20 g a.i./ha at 25 DAT) (T 6 ) were next best performing treatments, it had the potential to control broad spectrum of weeds i.e. broad, narrow leaved weeds and sedges. Weed control efficiency at harvest also recorded higher values in both the treatments.

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