Sweet sorghum, crucial for sugar and energy production, could help Egypt meet rising sugar demands but suffers from low productivity due to inadequate agronomic practices. Improving these practices could enhance its contribution alongside sugarcane and sugar beet. The aim of the research is to study Bio efficacy of different herbicides for economical weed management in sweet sorghum [Sorghum bicolor (L.) Moench] and their residual effect on succeeding crops. This experiment was carried out in Instructional Farm, Department of Agronomy, College of Agriculture, Junagadh Agricultural University, Junagadh (Gujarat). The experiment comprising 10 treatments was laid out randomized block design with three replications The sweet sorghum (SSV 84) was sown with standard package of practices. On the basis of the results obtained from the present two-years field study, it can be concluded that effective control of complex weed flora with profitable production in rabi sweet sorghum can be obtained by PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS. Saurashtra Agro-climatic Zone of Gujarat. There is no residual phytotoxicity of above mentioned pre and post-emergence herbicides through field bioassay.

Sweet sorghum, Herbicide, Weed Management, Bioassay, Herbicide Residue.

In India, sweet sorghum shares about 0.002 per cent area out of total sorghum area. The high WUE and low N requirements of sorghum also provide significant advantages to the growers, because sorghum fits into a normal rotation scheme with corn and soybeans, yet has lower production costs and employs similar production equipment. Its ratooning ability enables multiple harvests per season, a feature that could expand the geographical range of sorghum cultivation. The grain, stalk juice and bagasse can be used to produce food, fodder, ethanol and power. Owing to these favorable attributes, (Dar, 2012) refers to it as a SMART crop. It is known as the sugarcane of the desert and also ''the camel among crops'' for its drought hardy characteristics (Sanderson et al., 1992). These important characteristics, along with its suitability for seed propagation, mechanized crop production and comparable ethanol production capacity vis-a-vis sugarcane and sugar beet makes sweet sorghum a viable alternative source for ethanol production.

Among the various biotic factors limiting sweet sorghum production and productivity, weeds are of prime importance. (Bitzer, 1997) reported that plant density and weed management are among the main factors affecting growth, sugar and forage yields of sweet sorghum.  In India, presence of weeds in general reduces crop yields by                    37 - 45% and in some cases can cause complete crop failure, when compared to 25% due to diseases, 20% due to insects, 15% due to storage and miscellaneous pests (Bahadur et al., 2015). To prevent yield losses, weeds have to be controlled at critical periods during the crop growth cycle (Knezevic et al., 2002). (Silva et al., 2014) reported that on an average, weed can                         reduce the yield by 50% in sweet sorghum. Chemical weed control is a better supplement to conventional method and forms an integral part of the modern crop production. It is quick, more effective, time and labour saving method than others (Abbas et al., 2018). Success of chemical weed control methods depends upon several factors such as weed emergence pattern, application timing and stage of crop (Tanveer et al., 2019). Crop yield loss due to weed interference is one of the major threats to optimum crop production and global food security. Among various sorghum yield limiting factors, weed infestation remains a big challenge (Tuinstra et al., 2009).

Hence, the present study was undertaken to assess the Bio efficacy of different herbicides for economical weed management in sweet sorghum [Sorghum bicolor (L.) Moench]   and their residual effect on succeeding crops for weed control with better selectivity in sweet sorghum.

Experimental Location. A field experiment was conducted during rabi and summer seasons of 2022-23 and 2023-24 at Instructional Farm, Department of Agronomy, College of Agriculture, Junagadh Agricultural University, Junagadh and is situated at 21.5°N latitude and 70.5° E longitude with an altitude of 60 m above the mean sea level in South Saurashtra Agro-climatic Zone of Gujarat state, India. The dominant soil type of the area is clayey in texture. The experiment was laid out in a randomized block design with ten treatments and replicated thrice. Sweet sorghum (SSV 84) was sown at a spacing of 60 x 10 cm. The weed management treatments consisted of pre-emergence application (PE) of atrazine 50 WP 500 g/ha. The pre-emergence herbicide was supplemented with inter-cultivation and hand weeding (T1) or post-emergence application (PoE) of 2,4-D (SS) 95 SP (T2), halosulfuron- methyl 75 WG 60 g/ha (T3), topramezone 33.6 SC 25 g/ha (T4), clodinafop-propargyl 15 WP 60 g/ha (T5), tembotrione 42 SC 100 g/ha (T6), mesotrione + atrazine 44. 97 SC (Premix) 875 g/ha (T7), at 30 days after seeding (DAS), IC & HW at 15 and 30 DAS (T8), Weed free check (T9) and Unweeded control (T10). Pre-emergence herbicides were applied at 1 DAS and inter-cultivation/post-emergence herbicide, was applied at 30 DAS. All the pre-and post-emergence herbicides were applied with the help of knapsack sprayer fitted with flat fan nozzle and spray volume of 500 L/ha. The sweet sorghum was fertilized with 90-40-40 N-P2O5-K2O kg/ha and which were supplied to crop through urea (46% N), single super phosphate (16% P2O5, 12% S 21%, Ca) and muriate of potash (K 60%) respectively. Half of total N, entire P and K should be applied as basal dressing and the remaining N should be applied at 30 DAS. The rest of the packages of practices were adopted as per recommendations of the JAU. Category wise weed density and biomass were recorded randomly with the help of 0.25 m2 quadrat. The data on weed density and biomass were transformed to square root transformation to normalize their distribution. Weed control efficiency was computed as per the method suggested by (Mani et al., 1973). All the yield components were recorded at harvest. Benefit-cost ratio was calculated after dividing gross returns with cost of cultivation. The weed and crop data were analysed statistically as suggested by (Panse and Sukhatme 1985).

Effect on growth and yield attributes. An experiment of data revealed that among different treatments of weed management, the weed free check (T9) recorded significantly higher plant height at harvest during 2022-23, 2023-24 and in pooled results, respectively (Table 1), which was statistically at par with the IC & HW at 15 and 30 DAS (T8). Among the different weed management treatments, besides the weed free check (T9), IC & HW at 15 and 30 DAS (T8) higher number of panicles per m2, dry matter production per plant and yield attributing characters viz., number of earheads per m2, weight of earhead (g), weight of green millable stalk (g) (Table 2 and 3) were noticed under the PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) and PE application of atrazine 50 WP 500 g/ha fb IC & HW at 30 DAS (T1) in 2022-23, 2023-24, and pooled results. The improved yield attributes under weed free check (T9) and all other treatments might be due to periodical removal of weeds by hand weeding & interculturing as evidenced by less weed density and weed dry weight, which might have maintained high soil fertility status and moisture content by means of less removal of nutrients and water through weeds. This might have increased nutrients and water uptake by the crop leading to increased rate of photosynthesis.

The lowest value of growth parameters and yield attributes were recorded under the unwedeed check (T10) owing to severe competition by weeds for resources, which made the crop plant incompetent to take up adequate moisture, nutrients and light, consequently growth was suppressed owing to reduced photosynthesis and partitioning of photosynthates.  

These findings are in agreement with those of Galon et al. (2016); Simarmata et al. (2017).

Table 1: Effect of different treatments on plant height and number of tillers per m2 at harvest.

Table 2: Effect of different treatments on dry matter production (DMP) per plant and no. of earheads per m2 at harvest.

Table 3: Effect of different treatments on weight of earhead and weight of green millable stalk at harvest.

Effect on yield and quality parameters. Significantly higher grain, fodder yields, extraction (%) and extractability (kg/ha) of sweet sorghum were recorded under weed free check (T9), which remained statistically at par with the IC & HW at 15 and 30 DAS (T8), PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) and PE application of atrazine 50 WP 500 g/ha fb IC & HW at 30 DAS (T1) in 2022-23, 2023-24 and pooled results (Table 4 and 5). This may because of availability of more nutrients, resulting from reduced competition from weeds which were mobilized to grain thereby giving rise to higher grain and fodder yield. PE (atrazine) and PoE (mesotrione + atrazine 44.97 SC (Premix) applied herbicides with broad spectrum activity on grasses and broad-leaved weeds, supplemented with the manual weeding and interculturing in early and later stages compared to unweeded control and other herbicide treatments thereby resulting in a significant increase in sweet sorghum yield. The lowest values of yield and quality parameters were observed under the unweeded control (T10). The present findings are within the close vicinity of those reported with different weed management treatments by (Lagoke 1986; Mishra et al., 2012; Rao et al., 2013; Silva et al., 2014; Simarmata et al., 2017; Jantar et al.,2018; Saini et al., 2018; Mukherjee et al., 2019; Reis et al., 2019; Krishnamurthy et al., 2021).

Effect on weed density and biomass. At harvest, higher weed density and dry weight were registered under the unweeded control (T10). Among the different treatments, the weed free check (T9) recorded significantly the lowest weed density and dry weight, which is statistically at par to IC & HW at 15 and 30 DAS (T8). This is followed by the PE application of atrazine 50 WP 500 g/ha + IC & HW (T1) which is statistically at par with PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) in 2022-23, 2023-24. This might be due to inhibition of carotenoid biosynthesis by inhibiting the hydroxyphenylpyruvate dioxygenase (HPPD) enzyme, which results in plastoquinone (PQ) synthesis inhibition in weeds (Duke et al., 2000; Wichert et al., 1999; Takano et al., 2016; Simarmata et al., 2017).

At harvest highest weed control efficiency, lowest weed index was observed in the weed free check (T9) followed by IC & HW at 15 and 30 DAS (T8) due to excellent performance in controlling all the categories of weeds. This was followed by the PE application of atrazine 50 WP 500 g/ha + IC & HW (T1) with higher WCE and lower weed index followed by PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) in 2022-23, 2023-24, respectively (Table 7) due to broad-spectrum weed control and reduced total weed dry weight which led to higher yield. The lowest weed control efficiency and higher weed index was recorded under the unweeded control (T10), which indicates that the unrestricted weed growth reduced the sweet sorghum grain yield and fodder yield.

Economics. The data regarding gross returns furnished in Table 8 and Table 9 revealed that the maximum gross returns was obtained with the weed free check (T9), followed by IC & HW at 15 and 30 DAS (T8). The next best treatment was the PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) which might be due to the better seed and fodder yield in 2022-23, 2023-24 and average of both years, respectively. 

Concerned data indicated that the higher cost of cultivation was incurred with the weed free check (T9), followed by IC & HW at 15 and 30 DAS (T8) due to higher cost of manual weeding and interculturing which included labour and bullock pair charges. The next treatment with higher cost of cultivation was the PE application of atrazine 50 WP 500 g/ha fb IC & HW at 30 DAS (T1) incurred the pre-emergence herbicide cost, manual, interculturing cost of labours and bullock charges used for carried out the necessary operations followed by PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) due to cost of pre-emergence and post-emergence herbicides and its application cost. 

On an average of both the years (Table 9), the maximum net realization was achieved with the PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7) in 2022-23, 2023-24 and average of both the years, respectively, followed by PE application of atrazine 50 WP 500 g/ha fb IC & HW at 30 DAS (T1) in 2022-23, 2023-24 and average of both years, respectively. This might be due to effective and efficient control of weeds by integration of hand weeding and pre and post-emergence herbicides. 

Among different weed management treatments, higher B:C ratio was obtained with the PE application of atrazine 50 WP 500 g/ha fb mesotrione + atrazine 44.97 SC (Premix) 875 g/ha at 30 DAS, (T7), followed by atrazine 50 WP 500 g/ha as PE fb IC & HW at 30 DAS (T1) with B:C ratio in 2022-23, 2023-24 and average of both years, respectively. In contrast, the unweeded control (T10) recorded the lowest gross returns, net returns, cost of cultivation (only common cost) and B: C ratio, which might be due to declined yields due to the presence of excessive weed population. The results are on line with those of (Mitra et al., 2018; Yadav et al., 2018; Krishnamurthy et al., 2021; Verma et al., 2022).

Bioassay Studies. Bioassay is a major tool for quantitative and qualitative determination of herbicides persistence effect. In this method, the property of a chemical is measured in terms of some biological responses using indicator plants grown in a field and is compared with that of similar plant grown in untreated soil.

Residual effect on succeeding crops. The residual effect of different herbicides applied in sweet sorghum crop was found non-significant on germination percentage (10 DAS) of succeeding crops i.e., groundnut, sesame, pearl millet and soyabean (Table 10). The results clearly indicated that different herbicides viz., atrazine 50 WP 500 g/ha pre-emergence as well as 2,4-D (SS) 95 SP 500 g/ha, halosulfuron- methyl 75 WG 60 g/ha as PoE at 30 DAS, topramezone 33.6 SC 25 g/ha, Clodinafop-propargyl 15 WP 60 g/ha, tembotrione 42 SC 100 g/ha, fb mesotrione + atrazine 44. 97 SC (Premix) 875 g/ha as post-emergence herbicides did not leave their residual phytotoxic effect in the soil after harvesting of sweet sorghum crop on succeeding crops i.e., groundnut, sesame, pearl millet and soyabean. Hence, it is safe to sow groundnut, sesame, pearl millet and soyabean after harvesting of sweet sorghum crop in which pre-emergence application and post-emergence application have been made. Results corroborate with those of (Riddle 2012; Sharma et al., 2013; Nazreen et al., 2018; Yadav et al., 2018; Singh et al., 2019; Siabusu et al., 2020; Rani et al., 2022; Saimaheswari et al., 2022).

Table 4: Effect of different treatments on grain, dry fodder yield and harvest index at harvest.

Table 5: Effect of different treatments on extraction and extractability of sweet sorghum.

Table 6: Effect of different treatments on total weed density and dry weight at harvest.

Table 7: Effect of different treatments on weed control efficiency (%) and weed index at harvest.

Table 8: Economics of different treatment.

Table 9: Economics of different treatment.

Table 10: Phytotoxicity of different herbicides on germination per cent of succeeding crops.

Economical weed management strategies can make sweet sorghum more viable for small and marginal farmers, thus increasing its cultivation area. Research into the bio-efficacy of herbicides can directly support efforts to increase food security by improving crop yields and reducing losses due to weed competition. The research will be crucial in identifying herbicides that degrade quickly in the soil or safe for following crops, ensuring the long-term sustainability of agricultural systems. The findings can assist farmers in selecting rotational crops that are tolerant to herbicide residues or in adjusting herbicide application timing to mitigate adverse effects.