Evaluation of biorationals against fall armyworm Spodoptera frugiperda, in rabi sorghum

Introduction

Sorghum bicolor, commonly known as jowar, is an important cereal crop cultivated widely in semi-arid and tropical regions for both food and fodder purposes. It plays a crucial role in ensuring food and nutritional security, particularly in developing countries. However, sorghum production is severely affected by several insect pests. Among them, the fall armyworm, Spodoptera frugiperda (J.E. Smith), has recently emerged as a serious threat. Native to the Americas, this highly destructive lepidopteran pest has rapidly spread to Africa and Asia, including India. Its high reproductive potential, migratory behaviour and polyphagous feeding habit enable it to cause extensive damage to sorghum and other cereal crops. Larvae feed voraciously on leaves, leading to defoliation, reduced photosynthetic activity and significant yield losses. Therefore, effective and sustainable management strategies are essential to minimize the impact of fall armyworm on sorghum cultivation. In recent years, the invasive fall armyworm has emerged as a serious threat, causing nearly 16% yield loss in sorghum (Abrahams et al., 2017) [1] . Owing to its high fecundity, voracious feeding habit and polyphagous nature, it inflicts severe damage on crops, with reported yield losses in maize reaching up to 94.72% (Sena et al., 2003) [10] , along with its rapid spread across different regions (Goergen et al., 2016) [5] . Although chemical insecticides are widely used for its control, their excessive and indiscriminate application has resulted in the development of resistance, environmental pollution and adverse effects on non-target organisms. Therefore, sustainable management approaches, particularly the incorporation of host plant resistance within integrated pest management (IPM) strategies, are essential for effective control of fall armyworm.

Materials and methods

The research experiment entitled, "Evaluation of biorationals against fall armyworm Spodoptera frugiperda, in rabi sorghum" was conducted during rabi season, 2024-2025 at the Sorghum Improvement Project, MPKV, Rahuri, Maharashtra. The field efficacy of commercial biorationals against S. frugiperda on sorghum was evaluated in a randomized block design (RBD) with seven treatments replicated thrice including untreated control, with a plot size of 4.0 m x 2.7 m with inter and intra row spacing of 45 cm and 15 cm. The treatment details are mentioned in Table 1. All the recommended agronomic practices given by MPKV, Rahuri were followed to raise the crop. Observations were recorded after infestation was noticed in sorghum.

Methodology

The spraying was done manually as per given biorationals by a hand-operated knapsack sprayer with a hollow cone nozzle. Two foliar sprays of each treatment were given at an interval of 14 days at ETL. The first spray was given after the incidence was noticed. Untreated control was maintained by spraying water in the plot. The observation on per cent plant damage were recorded from each treatment plot. The data was recorded one day before spraying as a pre-count while post-treatment counts were taken at 5, 10 and 14 days after spraying (DAS). Observation at 14 days after first spray was related as pre count before second spray.

Per cent plant damage

The per cent damage was recorded from 30 plants per plot and calculated by using formula given by Mallapur et al.

(2018) [7] . Per cent plant damage = N/T x (100) Where, N = Total number of damaged plants per plot. T = Total number of plants per plot

Results and Discussion

After first spray

The data pertaining to effect of different treatments on per cent plant damage due to S. frugiperda at 5, 10 and 14 days after first spray is presented in the Table 2.

The pre count observation were nonsignificant indicating uniform FAW infestion in experimental field.

The data pertaining to mean per cent plant damage after first spray revealed that, mean per cent plant damage ranged from 5.89 to 16.67 % per 30 plants. The treatment chlorantraniliprole 18.50 % SC @ 0.4 ml/L was the significantly superior over all the treatments which recorded minimum per cent plant damage (5.89 per cent/30 plants). However, it was statistically at par with spinetoram 11.7 % SC @ 0.5 ml/L and emamectin benzoate 5 % SG @ 0.4 g/l which recorded 6.67 % and 7.78 % plant damage, respectively. The next best treatments were Metarhizium anisopliae @ 5 g/L, azadirachtin @ 2 ml/L and karanj oil @ 3 ml/L which recorded 11.11 %, 11.67 % and 11.85 % plant damage, respectively and were statistically at par with each other.

After second spray

The data pertaining to mean per cent plant damage after second spray revealed that, mean per cent plant damage ranged from 2.22 to 20.00 % per 30 plants. The treatment chlorantraniliprole 18.50 % SC @ 0.4 ml/L was superior over all the treatments which recorded minimum per cent plant damage of 2.22 per cent per 30 plants. However, it was statistically at par with spinetoram 11.7 % SC @ 0.5 ml/L and emamectin benzoate 5 % SG @ 0.4 g/L which recorded 3.33 % and 4.44 % plant damage, respectively. The next best treatments were Metarhizium anisopliae @ 5 g/L, azadirachtin @ 2 ml/L and karanj oil @ 3 ml/L which recorded 9.55 %, 10.00 % and 10.77 % plant damage, respectively and were statistically at par with each other. Cumulative effect of first and second sprays Data pertaining to cumulative mean efficacy of different biorationals against per cent plant damage showed that, treatment with chlorantraniliprole 18.50 % SC @ 0.4 ml/L. was found to be superior over all the treatments with minimum cumulative mean per cent plant damage of 4.07 % per 30 plants. However, it was followed by the treatment with spinetoram 11.7 % @ 0.5 ml/L. and emamectin benzoate 5 % SG @ 0.4 g/l. with cumulative mean per cent plant damage of 5.00 % and 6.11 % per 30 plants which were at par with each other. Next best treatments were M. anisopliae @ 5 g/l., azadirachtin @ 2 ml/L. and karanj oil @ 3 ml/L. with 10.33, 10.62 and 11.31 per cent plant damage per 30 plants respectively and were statistically at par with each other. On the other hand, untreated control recorded maximum mean per cent plant damage of 18.33 % per 30 plants after spray. The results obtained from the present investigation are in agreement with the findings of Bajracharya et al. (2020) [2] , who reported that emamectin benzoate (3.33 % plant infestation) was significantly superior to neem oil 1500 ppm (40.0 % plant infestation) in managing S. frugiperda infestation in maize. Similarly, Deshmukh et al. (2020) [3] found that efficacy testing of insecticides applied to crops planted in June and September 2018 revealed chlorantraniliprole 18.5% SC as the most effective treatment, followed by emamectin benzoate 5% SG. These insecticides not only provided effective control of S. frugiperda but also resulted in higher grain yields compared to the untreated control. Dileep Kumar and Murali Mohan (2020) and Masthan Shareef et al. (2020) [4] also reported that chlorantraniliprole 18.50% SC, emamectin benzoate 5% SG and spinetoram 11.7% SC were highly effective against S. frugiperda. Likewise, Sharanabasappa et al. (2020) [11] observed that chlorantraniliprole 18.5% SC @ 0.5 ml/l, emamectin benzoate 5% SG @ 0.4 g/l and spinetoram 11.7 SC @ 0.05 ml/l were highly toxic to S. frugiperda, indicating their strong efficacy in reducing the larval population of fall armyworm. Thumar et al. (2020) and Deshmukh et al. (2020) concluded that emamectin benzoate was on par with flubendiamide in its efficacy for managing S. frugiperda on sorghum and maize. Wayal et al. (2021) [14] revealed that Metarhizium anisopliae @ 50 g/10 l was the most effective biopesticide in reducing plant damage (57.04 %) caused by S. frugiperda. Similarly, Jahan (2022) [6] reported the highest per cent reduction (52.02 %) of leaf infestation in the treatment with M. anisopliae @ 8 g/l. Furthermore, Ramanujam et al. (2020) [9] concluded that M. anisopliae ICAR-NBAIR Ma 35 strain exhibited a 70 % reduction in S. frugiperda infestation.

Grain yield

The data of grain yield presented in Table 5. revealed that grain yield ranged from 35.00 to 51.80 q/ha, showing substantial variation among the treatments. Significantly higher grain yield was recorded in the plot treated with chlorantraniliprole @ 0.4 ml/l (51.80 q/ha), which was superior to all other treatments. The next best yield was obtained from the plot treated with spinetoram @ 0.5 ml/l (50.32 q/ha), followed by emamectin benzoate @ 0.4 g/l (47.36 q/ha). The plot treated with Metarhizium anisopliae @ 5 g/l (40.44 q/ha) which was statistically at par with azadirachtin @ 2 ml/l (40.00 q/ha) and karanj oil @ 3 ml/l (39.80 q/ha). The lowest grain yield was recorded in the untreated plot (35.00 q/ha).

Fodder yield

The data on fodder yield presented in Table 5. revealed that the yield varied from 91.00 to 136.16 q/ha, showing substantial variation among different treatments. Significantly higher fodder yield was recorded in the plot treated with chlorantraniliprole @ 0.4 ml/l (136.16 q/ha), which was superior to all other treatments. The next best yield was obtained from the plot treated with spinetoram @ 0.5 ml/l (131.72 q/ha), followed by emamectin benzoate @ 0.4 g/l (125.80 q/ha). The plots treated with Metarhizium anisopliae @ 5 g/l (106.56 q/ha), followed by azadirachtin @ 2 ml/l (99.16 q/ha) and karanj oil @ 3 ml/l (96.20 q/ha) recorded comparatively lower yields. The minimum fodder yield was recorded in untreated plot (91.00 q/ha).

The present findings are in agreement with those of Sharanabasappa et al. (2020) [11] , who reported that chlorantraniliprole 18.50% SC recorded the highest grain yield of maize (66.50 q/ha), followed by emamectin benzoate 5 SG (65.17 q/ha) and spinetoram 11.7% SC (64.67 q/ha) whereas, the untreated control recorded the lowest grain yield (32.46 q/ha). Similarly, Sunilkumar et al. (2020) [12] demonstrated that the application of chlorantraniliprole 18.5% SC resulted in the highest maize grain yield (77.42 q/ha), followed by spinosad 45% SC, spinetoram 11.7% SC and emamectin benzoate 5% SG, due to their effective control of Spodoptera frugiperda. Furthermore, Thumar et al. (2020) [13] concluded that spinetoram 11.7% SC was highly effective in suppressing the larval population of maize fall armyworm, which was reflected in higher grain and fodder yields, followed by emamectin benzoate 5% SG, chlorantraniliprole 18.50% SC and thiodicarb 75% WP.

Incremental cost benefit ratio of biorationals on yield of sorghum

The incremental cost benefit ratio (ICBR) presented in Table 4.19 revealed that maximum ICBR (1:14.60) was obtained from treatment with emamectin benzoate @ 0.4 g/l. The next highest ICBR was recorded in chlorantraniliprole @ 0.4 ml/l (1:8.47), followed by spinetoram @ 0.5 ml/l (1:7.15). The plots treated with M. anisopliae @ 5 g/l recorded an ICBR of (1:6.53), followed by azadirachtin @ 2 ml/l (1:1.66) and karanj oil @ 3 ml/l (1:1.35).

Conclusion

Among the evaluated biorational insecticides, chlorantraniliprole 18.5% SC and spinetoram 11.7% SC demonstrated superior performance by significantly reducing the percentage of plant damage after both spray applications. With respect to the incremental cost benefit ratio (ICBR), emamectin benzoate 5% SG emerged as the most economical option, primarily due to its lower plant protection cost. Metarhizium anisopliae 1.15% WP exhibited moderate effectiveness and may be recommended as a safer and environmentally sustainable alternative, especially for organic and low-residue production systems. In contrast, azadirachtin (10000 ppm) and karanj oil recorded comparatively lower efficacy; however, they can still play a supportive role in integrated pest management programs when applied in combination with other control measures.

Acknowledgement

AcknowledgementI am grateful to Dr. U.K. Kadam, Dr. U.S. Dalvi Dr. R.S. Bhoge and Dr. V.B. Shinde for their invaluable guidance and support throughout my research work. Their expertise and encouragement have been instrumental in shaping this endeavour.

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