Groundnut (Arachis hypogaea L.) is a vital oilseed crop extensively cultivated in tropical and subtropical climates for its high oil content, protein-rich kernels and its role in improving soil fertility. However, one of the major constraints affecting groundnut productivity is weed infestation, particularly during the early stages of crop growth. Weeds compete aggressively with groundnut plants for essential resources such as nutrients, moisture, sunlight and space, leading to significant yield losses if not effectively managed (Sahoo et al., 2024). Conventional weed control practices, including manual weeding and herbicide application are commonly employed in groundnut cultivation. Knapsack sprayers are widely adopted by smallholder farmers due to their low cost and ease of use. However, they are labor-intensive, time-consuming and often result in uneven herbicide distribution, leading to inefficient weed control and potential crop injury. In recent years, Unmanned Aerial Vehicles (UAVs) have emerged as a promising tool in precision agriculture, offering a modern alternative for herbicide application. UAV sprayers provide several advantages over conventional methods, including more uniform chemical distribution, reduced herbicide usage, minimal crop disturbance and the ability to cover large or difficult to-access areas efficiently (Hemalatha et al., 2025). By precisely controlling variables such as spray height and volume, UAVs can significantly improve application accuracy and reduce herbicide drift, making them a viable option for sustainable and efficient weed management. Recognizing the need for improved application techniques in groundnut cultivation, this study aims to evaluate the comparative effectiveness of UAV and knapsack sprayers in herbicide application. The goal is to determine a more efficient, cost-effective and environmentally responsible approach to weed control that enhances groundnut productivity while minimizing labor demands and chemical wastage.

A field experiment was conducted during the rabi seasons of 2022-23 and 2023-24 at the Regional Agricultural Research Station (RARS) Farm, Palem, Nagarkurnool District, Telangana, India, on sandy loam soil. The experiment was laid out in a factorial randomized block design (FRBD) comprising 12 UAV-based herbicide spray treatments, while five conventional check treatments were evaluated separately outside the main experimental layout. All treatments were replicated thrice. Treatment details of the experiment were given below (Table 1).


 
UAV-based herbicide application
 
An AGRICOPTER AG 365 UAV, powered by a lithium-ion battery, was used for aerial spraying. The drone was equipped with a 10-liter chemical tank and four XR11002VP nozzles symmetrically mounted on both sides of the fuselage, which spanned at 1.2 meters. The nozzles were installed at an angle of 110° and the drone maintained a spray width of 4.0 meters.
       
Two operating heights (2.0 and 2.5 m above the crop canopy) and two spray fluid volumes (25 L ha^-1 and 40 L ha^-1) were tested. Flight speeds were adjusted to deliver the required volume 5.0 m s^-1 for 25 L ha^-1 and 2.7 m s^-1 for 40 L ha^-1. The UAV operated at 60% discharge capacity with nozzle pressure maintained at 2.0 bar. Applications were made at 20 DAS when groundnut and weeds were at the 2-3 leaf stage. 
 
Weed density (m^-2)
 
The total number of weeds was taken from each plot at randomly selected representative locations with the help of the quadrate of 0.25 m² before application, 15 and 30 DAA. At every stage of sampling, the total number of weeds was counted and data were presented per m² and subjected to statistical analysis after square root transformation with following formula.
 

 
Where,
X= Transformed value.      
x= Original value.

Weed dry weight (g m^-2)
 
Weeds were removed from the sampling area of the plot before application of the PoE herbicide, 15 and 30 days after application of the herbicide (DAA). Then, the roots were removed and the weeds were shade dried initially, followed by oven drying at 60°C to a constant weight and the weed dry weight in different treatments was expressed in g m^-2. The weed dry matter data was subjected to square root transformation before statistical analysis.
 
Weed control efficiency (%)
 
Weed control efficiency of different treatments was computed based on the weed dry matter using the following formula (Mani et al., 1973).

 
Where,
WCE= Weed control efficiency (%).
DMc= Dry matter of weeds in the unweeded control.
DMt= Dry matter of weeds in the treatment plot.
 
Pod yield (kg ha^-1)
 
The total pod yield was weighed and expressed in kg ha^-1.
 
Statistical analysis
 
The data recorded were statistically analyzed following the ANOVA for factorial randomized block design as suggested by Panse and Sukhatme (1978). The contrast analysis was also performed and P values were computed to compare the means of UAV-based application against knapsack spraying, unweeded control and weed-free plots.

Weed flora
 
The experimental plots contained weed species from eight botanical families. The flora comprised three grass species, one sedge and six broad leaved weeds. The predominant grasses were Cynadon dactylon (Bermuda grass), Dactyloctenium aegyptium (crow foot grass) and Digitaria sanguinalis (large crab grass). The sedge identified was cyperus rotundus (purple nut sedge). The broad leaved weed group included Acalypha indica, Boerhavia diffusa, Commelina benghalensis, Cardispermum halicocabum, Digeria arvensis and Parthenium hysterophorus.
 
Weed density and dry matter
 
The application of herbicide mixture (Imazethapyr and Propaquizafop) in rabi groundnut significantly influenced both weed density and dry matter, with higher herbicide doses resulting in more effective weed suppression. Across the 2022-23 and 2023-24 seasons, weed density and biomass were consistently highest at the 75% herbicide dose and declined progressively with the 100 and 125%, indicating a dose-dependent response as shown in Fig 1 and 2. At both 15 and 30 days after application (DAA), the lowest weed density and dry matter were recorded at the 125% dose, emphasizing the efficacy of higher doses in reducing weed proliferation and growth.These findings conform to other studies of imazethapyr (Dass et al., 2019). Spray volume and application height also played a critical role, where 40 L ha^-1 and a spray height of 2.0 m led to significantly lower weed counts and dry matter accumulation compared to 25 L ha^-1 and 2.5 m, respectively. These trends were consistent in both years of the study. Notably, interaction effects among herbicide dose, spray volume and application height were significant, further influencing weed suppression outcomes. From Fig 1 and 2 comparison between application methods revealed that knapsack sprayers (500 L ha^-1) were more effective in reducing weed density and biomass. However, among drone treatments, a higher spray volume (40 L ha^-1) and lower height (2.0 m) improved herbicide efficacy. Overall, these findings underscore the importance of optimizing both herbicide dose and application parameters for effective weed management, aligning with the results of earlier studies by Kalhapure et al., (2013); Kundu et al., (2015); Jeevan et al., (2023) and Paul et al., (2023).




 
Weed control efficiency
 
In 2022-23, weed control efficiency observed, at 15 DAA was ranged between the 49.5 to 76.1% and at 30 DAA, it was 68.3 to 85.1%. Similarly, in 2023-24, WCE (%) was ranged between 50.1 to 74.5% at 15DAA, at 30 DAA the WCE (%) was in the range of 71.8 to 85.8% as shown in Table 2 respectively.


       
The highest WCE (%) was observed in KS _1.25X and lowest was noted in the T₂ (D₁-75%,S₁-25 L ha^-1, H₂-2.5m) at 15, 30 DAA in both the years of the study. These results are in line with findings of the Laxmidevi et al. (2022) and Sharma et al. (2017) who reported the groundnut weed control efficiency ranges from 47 to 88%.
 
Pod yield
 
Pod yield was markedly influenced by herbicide dosage, spray volume and spray height under UAV application. Across both seasons, the recommended dose (100%) consistently produced maximum yields, statistically comparable with 125% but significantly superior to75%. Due to the phytotoxicity at the 125% dose of the herbicide, recommended dose has observed the highest yield. Application from 2.0 m above the crop canopy resulted in significantly higher yields than 2.5 m, while spray volume (25 vs. 40 L ha^-1) alone exhibited no significant effect, indicating that herbicide dose and spray height were the critical factors governing yield response as shown in Table 3 and 4.




       
Significant interaction effects among herbicide dose, spray volume and spray height were evident. In both years, the combination of 100% herbicide with 40 L ha^-1 spray volume at 2.0 m height registered the maximum yields (3484 and 2769 kg ha^-1 in 2022-23 and 2023-24) as shown in Table 3 and 4. In contrast, the lowest yields consistently occurred with 75% applied at 25 L ha^-1 from 2.5 m height. The superior performance at 2.0 m spray height may be attributed to greater spray deposition and enhanced herbicide coverage, which improved weed suppression, reduced crop-weed competition and facilitated higher biomass accumulation.
       
Yield comparisons between UAV and knapsack sprayer applications revealed no significant differences at equivalent herbicide dosages, suggesting UAVs as an efficient alternative delivery system. Notably, UAV application at 40 L ha^-1 demonstrated enhanced effectiveness, likely due to improved droplet size distribution, uniform soil coverage and optimized deposition, which collectively contributed to better nodulation, resource use efficiency, source-sink dynamics and ultimately higher pod yields.
       
The overall findings highlight UAV spraying as a promising alternative to conventional methods, capable of delivering effective weed control and higher pod yields. Similar observations have been reported in earlier studies (Divyamani et al., 2018; Jitendra et al., 2022; Ahmad et al., 2020; Rawat et al., 2014), confirming that recommended herbicide doses combined with optimal spray height and volume can significantly improve groundnut productivity.

The study found that the application of the recommended dose (100%) of Imazethapyr + Propaquizafop, applied at 40 L ha^-1 from 2.0 m above the canopy, consistently resulted in the highest weed control efficiency and pod yield in groundnut. UAV spraying at the recommended herbicide dose and optimized application parameters proved to be an effective and sustainable alternative to conventional knapsack spraying, ensuring efficient weed control better resource utilization and enhanced productivity. The lower labour input and greater operational efficiency of UAV spraying contributed to improved economic returns, demonstrating its potential as a cost-effective and sustainable weed management strategy in groundnut cultivation.

Authors dont have no conflict of interest.