Comparative assessment of novel herbicide molecules and their effects on weed dynamics in sugarcane

Introduction

Sugarcane (Saccharum spp. hybrid complex) is an important commercial crop grown across a wide latitudinal range from 8°N to 30°N in India, encompassing diverse climatic and soil conditions. India holds the position of the world's second-largest sugar producer (Patel et al., 2018) [10] . Due to its relatively long germination period, wide row spacing, slow initial growth, lateral spreading habit, heavy fertilizer requirements, and frequent irrigation, sugarcane fields create an ideal environment for weed growth. Weeds often emerge before the sugarcane crop, negatively impacting germination, overall yield, and crop quality. Previous studies have reported that yield losses caused by weed infestation can vary widely, ranging from 10% to complete crop failure (Srivastava and Chauhan, 2002) [14] . The period of intense crop-weed competition, particularly within the first 120 days after planting, is considered the most critical for controlling weeds, as weed pressure during this stage causes the greatest harm. Therefore, effective weed management during this critical period is essential to maximize sugarcane yield. It is evident from various experimental results that, integration of different weed control methods is an effective tool for better weed control in sustainable manner. But in recent years, non-availability of labour forced to farmers to relay on chemical weed management and this is easier, time saving and economical intervention. In this context, there is need to evaluate new pre and post-emergence herbicides and the sequential application of two herbicides with different mode of action for the effective management of complex weed flora in sugarcane. Keeping this in mind the field experiment was conducted to evaluate the efficacy of new herbicide molecules for weed management in sugarcane.

Materials and Methods

The study was carried out over two consecutive years, 2023-24 and 2024-25 under the AICRP's program, at the Vasantdada Sugar Institute's research farm located in Manjari, Pune, on vertisol soil. The experimental site is situated at a latitude of 18.5262° N and longitude of 73.9746° E, with an elevation of 551 meters above sea level. A randomized block design (RBD) was employed for the experiment, consisting of nine different weed management treatments with three replications each. Among these treatments, two served as controls: a weedy check and a weed-free check. The remaining seven treatments involved combinations of herbicides and cultural practices. Details of these treatments are presented in Table 1. Each gross plot measured 7.00 meters in length and 6.85 meters in width (covering five rows), while the net plot size was 6.00 meters by 4.11 meters (three rows). The fertilizer regime for the early sugarcane crop followed the recommended dose of 250 kg nitrogen, 115 kg phosphorus (P 2 O 5 ), and 115 kg potassium (K 2 O) per hectare. Nitrogen was applied in four split doses, while phosphorus and potassium were applied half at planting and the remaining half during the final earthing up. Throughout the experimental period, the predominant weed species observed included Cynodon dactylon, Cyperus species, Convolvulus arvensis, Parthenium hysterophorus, Ipomoea species, Chenopodium album, and Euphorbia hirta among others. Weeds from one-meter square were taken from the quadrate from each plot. Weeds were air-dried followed by oven dried at 65 0 C ±2 for 48 hrs. and weighed. The effect of tested herbicide on density (no./m 2 ) and dry weight of weeds (g/m 2 ) was recorded at 30, 60, 90 and 120 DAP and the data were transformed on squre root transformation by adding 1 to original value prior to statistical analysis. calculate the weed control efficacy (WCE) by using formula given by Mani et al. (1973) [5] as followed.

Where, WDc= Dry weight of weed in control WDt= Dry Weight of weed in treatment Further to know the losses caused by weeds in sugarcane, weed index was computed as procedure given by Gill and Kumar (1969) [2] using the following formula:

Where, X= Yield from weed free plot Y= Yield of plot for which WI is calculated Data on yield, quality, and contributing factors were collected throughout the entire growing season. The number of tillers was recorded at 120 days after planting, whereas all other parameters were assessed at harvest. The count of millable canes (NMC) was taken during harvest as well. Cane juice was extracted using a power crusher to evaluate quality, with brix and sucrose content measured following the procedure described by Meade and Chen (1977) [7] . Sucrose percentage was calculated using Schmitz's Tables. Commercial cane sugar (CCS) percentage was computed using the formula: CCS% = {Sucrose% -(Brix% -Sucrose%) × 0.4} × 0.74. The collected data on cane yield and related parameters were subjected to statistical analysis and interpretation according to the methods outlined by Panse and Sukhatme (1978) [9] . Economic analysis was also performed.

Results

Growth attributes

The data clearly indicated that the growth attributes of sugarcane were significantly influenced by different weed management practices. The highest crop emergence (63.22%) was recorded under the treatment with pre-emergence (PE) application of Clomazone 30% + Sulfentrazone 28% WP (ready mix) at 2.5 kg/ha, followed by one intercultivation at 60 DAP (partial earthing up). In contrast, the treatment involving PE application of Clomazone 22.5% + Metribuzine 21% WP (ready mix) at 2.5 kg/ha followed by one intercultivation at 60 DAP (partial earthing up) resulted in a significantly higher tiller population (103.00 thousand/ha) at 120 DAP and millable cane population (92.25 thousand/ha) at harvest. These findings align closely with those reported by Worku Tadele et al. (2022) [15] , Singh et al.

(2016) [12] , and Ombase et al. (2019) [8] , who also noted that effective weed control positively influences sugarcane growth and plant stand.

Yield and yield attributes

The yield attributes of sugarcane were markedly influenced by different weed management strategies (Table 2). The highest single cane weight (1.36 kg) was recorded under the treatment involving PE application of Clomazone 30% + Sulfentrazone 28% WP (ready mix) at 2.5 kg/ha, followed by one intercultivation at 60 DAP and PoE application of Halosulfuron methyl + Metribuzine (ready mix) @ 1 L/ha at the 2-4 leaf stage of weeds with earthing up at 120 DAP. The superior yield performance under these treatments can be attributed to effective early weed suppression, which minimized crop-weed competition and facilitated better nutrient uptake and growth. These findings are in line with the reports of, Maurya et al. (2020) [6] , who also highlighted the effectiveness of halosulfuron + metribuzin and related herbicidal combinations in enhancing cane productivity.

Weed Studies

The impact of various weed management practices on weed density, weed dry matter, and weed control efficiency was assessed at 30, 60, 90, and 120 DAP (Tables 456789101112). All parameters were significantly influenced by the treatments. The weedy check recorded the highest population of monocots, dicots, and sedges, whereas all weed management treatments significantly reduced weed growth and maintained better control throughout the crop period.

Weed density

At 30, 60, and 90 DAP, the lowest monocot weed counts were observed with pre-emergence application of Clomazone 22.5% + Metribuzine 21% WP (2.5 kg/ha) followed by intercultivation at 60 DAP, closely followed by Clomazone 30% + Sulfentrazone 28% WP. By 120 DAP, Clomazone + Sulfentrazone showed the best monocot control. For dicot weeds, Topramezone + Atrazine (PoE at 3 L/ha) reduced counts significantly at 30 DAP, while Halosulfuron methyl + Metribuzine (PoE at 1 L/ha) effectively minimized dicot density at 60 and 90 DAP, comparable to other herbicide combinations. At 120 DAP, Clomazone + Sulfentrazone provided the most sustained broadleaf weed control. Halosulfuron methyl + Metribuzine (PoE) also recorded the lowest sedge population. Total weed density was lowest with Topramezone + Atrazine at 30 DAP, but Clomazone + Sulfentrazone (PE) plus intercultivation effectively reduced total weed numbers at later stages (60-120 DAP).

At 30, 60, and 90 DAP, pre-emergence (PE) application of Clomazone 22.5% + Metribuzine 21% WP (2.5 kg/ha) followed by intercultivation at 60 DAP effectively reduced grass dry matter early on. By 120 DAP, Clomazone 30% + Sulfentrazone 28% WP (PE at 2.5 kg/ha) maintained the lowest grass biomass, indicating strong residual control. For broadleaf weeds, post-emergence (PoE) application of Topramezone + Atrazine (3 L/ha) at 30 DAP showed the greatest early reduction in dry matter. Halosulfuron methyl + Metribuzine (PoE at 1 L/ha) sustained broadleaf suppression at 60 and 90 DAP, while Clomazone + Sulfentrazone (PE) provided the most consistent control through 120 DAP. Sedge dry matter was lowest under PoE Halosulfuron methyl + Metribuzine at all stages. Total weed dry weight was minimized by Clomazone + Sulfentrazone at 30 and 120 DAP, highlighting its long-term efficacy. Meanwhile, Halosulfuron methyl + Metribuzine excelled in reducing total weed biomass during mid-season (60 and 90 DAP). Together, these treatments offered effective, complementary weed control throughout the growing season.

Weed control efficiency

At 30 and 120 DAP, pre-emergence application of Clomazone 30% + Sulfentrazone 28% WP (2.5 kg/ha) followed by intercultivation at 60 DAP showed the highest weed control efficiency due to its strong residual and broad-spectrum activity. In contrast, post-emergence application of Halosulfuron methyl + Metribuzine (1 L/ha) at the 2-4 leaf stage, followed by earthing up at 120 DAP, was most effective at 60 and 90 DAP, providing superior mid-season weed suppression. These results are consistent with Tropaldi et al. (2021) [16] , who highlighted the prolonged residual control of the Clomazone + Sulfentrazone mixture under tropical conditions. Additionally, the FMC Authority NXT Technical Bulletin (2020) [1] endorses this premix at 2.5 kg/ha for effective early-season weed management in sugarcane, supporting the findings of this study.

Weed Index and economics

Treatment PoE application of Halosulfuron methyl + Metribuzine (ready mix) @1 L/ha at 2-4 leaf stage of weeds fb earthing up at 120 DAP noted lowest weed index (10.40) and highest B:C ratio (1:2.38). Chaturvedi et al. (2020) observed that halosulfuron methyl in combination with metribuzin provided superior weed suppression and higher net returns compared with single-herbicide molecule.

Acknowledgement

AcknowledgementThe authors express their sincere gratitude to Mr. Sambhaji Kadupatil, Director General of Vasantdada Sugar Institute, Pune, for his encouragement and for granting permission to publish this article. Appreciation is also extended to the scientists and support staff of the Crop Production Division for their valuable assistance during the field experiments.

References

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