Effect of VLCFA, ALS and 4-HPPD inhibitors on weeds, yields and economics of Kharif hybrid maize (Zea mays L.) in Varanasi

Introduction

Maize (Zea mays L.), often referred to as the "queen of cereals," is a globally significant crop due to its high yield potential and diverse applications in food, feed, fodder, and biofuel industries (Bamboriya et al., 2024) [2] . Cultivated across 193 million hectares in 170 countries, maize production reached approximately 1.2 billion metric tonnes in 2021, with the United States, China, Brazil, and India being the leading producers (FAO, 2021) [4] . While the United States records maize productivity exceeding 10 t/ha, India lags significantly behind, with an average productivity of 2.96 t/ha, which is half the global average (Anonymous, 2024) [1] . Among several factors limiting maize productivity in India, weed infestation remains a critical challenge, particularly due to the slow initial growth, wide row spacing, and frequent rainfall during the rainy season, which creates a favorable environment for weed proliferation. Weeds compete with maize for light, nutrients, moisture, and space, affecting crop morphology, phenology, and grain quality while increasing harvesting difficulties and production costs. In extreme cases, unchecked weed growth can cause yield losses of up to 90%, depending on weed species and density (Patel et al., 2006) [13] . Consequently, effective weed management is crucial to realizing the full yield potential of maize (Malviya and Singh, 2001) [10] . The scarcity of agricultural labor has further complicated weed control during critical crop growth stages, making herbicide application the most practical and widely adopted approach for weed management in maize. Herbicides are applied at different growth stages, including pre-plant, pre-emergence, and post-emergence, depending on field conditions and weed spectrum (Chauhan et al., 2017) [3] . The use of herbicide mixtures and sequential applications has proven effective in achieving season-long weed control.

Atrazine, in particular, is widely used by farmers due to its flexibility in application (pre-and post-emergence), broadspectrum control, lower cost, and compatibility with other herbicides. However, the excessive and repeated use of atrazine has led to herbicide resistance and weed flora shifts, with 45 weed species worldwide exhibiting resistance to photosystem II (PSII) inhibitors like atrazine. This necessitates the adoption of alternative herbicide modes of action combined with mechanical weed control practices to mitigate the risk of resistance and ensure sustainable maize production. The objective of this study is to assess the efficacy of VLCFA (very-long-chain fatty acid inhibitors), ALS (acetolactate synthase inhibitors), and 4-HPPD (4-hydroxyphenylpyruvate dioxygenase inhibitors) herbicides, along with integrated weed management strategies, in suppressing weeds at 50 DAS, enhancing yield, and improving the economic viability of maize cultivation under the agroclimatic conditions of Varanasi, Uttar Pradesh. This research aims to develop a sustainable and efficient weed management approach that not only ensures higher crop productivity and profitability for farmers but also mitigates the risks of herbicide resistance and environmental degradation.

Materials and Methods

A field study was conducted in Kharif season of 2023-24 at Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India (latitude of 25°18' N and a longitude of 83°03' E, at an elevation of 75.7 meters above mean sea level). The experimental site had sandy clay loam soil, neutral pH (6.9), low organic carbon (0.36%), low available nitrogen (178.24 kg/ha), medium phosphorus (22.64 kg/ha), medium potassium (204.35 kg/ha), and normal electrical conductivity (0.17 dS/m). The experiment was laid out in a randomized block design (RBD) with three replications, evaluating twelve weed management treatments: T 1 -weedy check (no intervention); T 2 -weed-free check; T 3 -atrazine at 500 g/ha plus hand weeding at 25-30 DAS; T 4 -pyroxasulfone at 127 g/ha plus hand weeding; T 5 -atrazine (500 g/ha) followed by halosulfuron methyl at 67 g/ha; T 6atrazine (500 g/ha) followed by tembotrione at 120 g/ha; T 7atrazine (500 g/ha) followed by topramezone at 25 g/ha; T 8atrazine (500 g/ha) with a mesotrione+atrazine mix at 300 g/ha; T 9 -pyroxasulfone (127 g/ha) followed by halosulfuron methyl (67 g/ha); T 10 -pyroxasulfone (127 g/ha) followed by tembotrione (120 g/ha); T 11 -pyroxasulfone (127 g/ha) followed by topramezone (25 g/ha); and T 12 -pyroxasulfone (127 g/ha) followed by mesotrione + atrazine (300 g/ha). All chemical applications were made at 25-30 DAS. Following pre-irrigation and double plowing in a criss-cross pattern after the mustard harvest, the field was tilled, and maize (CP 858) was sown manually at 25 kg/ha with rows 60 cm apart and plants 20 cm apart. Fertilizers were applied at 150 kg N/ha, 70 kg P₂O₅/ha, and 60 kg K₂O/ha with half the nitrogen applied at sowing and the remainder split at 30 and 55 DAS. Five irrigations were scheduled at critical growth stages (2-leaf, knee-height, tasseling, silking, and grain-filling). Herbicides were applied using a knapsack sprayer calibrated at 500 L/ha. Grain and stover yields (adjusted to 14% moisture) were expressed in quintals per hectare. Plant growth attributes were measured from randomly selected plants, and weed density and dry weight were assessed at 50 DAS using 1 m² quadrats. An economic analysis was performed based on input and operational costs, and data were analyzed by ANOVA with treatment differences evaluated using CD and DMRT (Gomez & Gomez, 1984) [5] in SPSS.

Results and Discussion

The application of different herbicidal treatments significantly influenced total weed density and dry weight of grasses, sedges, and broad-leaved weeds (BLW) at 50 DAS (Table 1). Among the treatments, T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) was the most effective, significantly reducing weed density and dry weight while recording higher weed control efficiency (96%) and lower weed index (4%), outperforming atrazine-based treatments at 50 DAS. This was followed by T 12 (Pyroxasulfone 127 g/ha fb Mesotrione + Atrazine 300 g/ha) and T 3 (Atrazine 500 g/ha fb hand weeding at 25-30 DAS), which were statistically at par with T 4 in reducing weed infestation, although slightly less effective. Among the atrazine-based treatments, T 3 significantly reduced weed density and dry weight compared to T 5 (Atrazine 500 g/ha fb Halosulfuron Methyl 67 g/ha) and T 6 (Atrazine 500 g/ha fb Tembotrione 120 g/ha). However, T 5 , T 6 , and T 7 (Atrazine 500 g/ha fb Topramezone 25 g/ha) were statistically at par with each other but exhibited higher weed biomass accumulation compared to pyroxasulfonebased treatments, highlighting atrazine's limited efficacy against grassy weeds. The superior weed suppression in pyroxasulfonebased treatments is attributed to its long residual activity and inhibition of very-long-chain fatty acid (VLCFA) biosynthesis, preventing weed emergence and regrowth (Mahoney et al., 2014) [11] . The inclusion of hand weeding in T 4 further enhanced its weed control potential. In contrast, atrazine-based treatments, though effective against broadleaf weeds, had limited efficacy on grasses and raised concerns about herbicide resistance (Heap, 2014; Shaner and Beckie, 2014) [6,16] . Overall, T 4 (Pyroxasulfone 127 g/ha fb hand weeding) emerged as the most effective treatment, followed by T 12 and T 3 , ensuring seasonlong weed suppression and better maize yield potential (Chauhan et al., 2017) [3] . Weed management treatments significantly influenced maize growth parameters, yield, and economic returns (Table 2). At 50 DAS, the weed-free treatment recorded the highest number of leaves per plant, leaf area index (LAI), chlorophyll content (SPAD) and yield parameters whereas the weedy check exhibited the lowest values, highlighting the impact of weed competition on crop growth. Among herbicidal treatments, T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) outperformed T3 (Atrazine 500 g/ha fb Halosulfuron Methyl 67 g/ha) in terms of number of leaves per plant (11.3), LAI (0.42) and chlorophyll content (39.6). Maize yield was notably influenced by weed control practices, with T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) recording higher seed index (29.4), grain yield (5.61 t/ha), stover yield (8.14 t/ha), and harvest index (40.82) than T 3 (Atrazine 500 g/ha fb Halosulfuron Methyl 67 g/ha). This improvement in yields can be attributed to better reproductive parameters, including higher numbers of cobs per plant, more grain rows per cob, increased grains per row, and greater seed index. These findings align with the research of Ramos et al. (2017) [15] , who demonstrated that effective weed control significantly improves maize productivity. Economic analysis revealed that T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) achieved the higher net return (120741.8 ₹/ha) and benefit-cost (B:C) ratio of 3.24 in contrast with T 3 (Atrazine 500 g/ha fb Halosulfuron Methyl 67 g/ha). This was attributed to higher economic yield, net return and lower cost of cultivation, making it the most economically viable herbicidal treatment. The findings emphasize the need to balance weed control efficiency, yield improvement, and costeffectiveness for sustainable maize production (Kashe et al. 2020) [8] . The study concludes that T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) was the most effective herbicidal treatment for weed suppression in Kharif hybrid maize at 50 DAS. It significantly reduced weed density and biomass, achieved higher WCE and lower WI, and resulted in higher yields and economic returns. Given the limitations of atrazinebased treatments, adopting herbicides with diversified modes of action and integrated weed management (IWM) strategies is essential for effective weed suppression, yield maximization, and economic sustainability in maize cultivation. Thus, for effect weed control at 50 DAS, higher yields and economic return of Hybrid maize, T 4 (Pyroxasulfone 127 g/ha fb hand weeding at 25-30 DAS) can be suggested under the agroclimatic conditions of Varanasi, Uttar Pradesh. The values of parenthesis were the original values that had been changed to√(X+0.5); PE-Pre-emergence; DAS-Days after sowing

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