Sorghum (Sorghum bicolor L.) is an important cereal crop (FAO, 2018), and in Tamil Nadu, it is grown in drought-prone, marginal areas. In Tamil Nadu it is cultivated in an area of 3.85 lakh ha with a productivity of 1117 kg/ ha (AICSIP, 2021). The yield of sorghum is largely affected by biotic constraints and >150 insect species infest sorghum. Damage inflicted by these cause serious losses (Daware et al., 2012). In India, shoot fly and stem borer significantly reduce the yield, at times as high as 100% in grain and crop stand (Padmaja et al., 2010). In Tamil Nadu, shoot fly Atherigona soccata Rondani, stem borer Chilo partellus Swinhoe and grain midge Stenodiplosis sorghicola Coquillett are the regular pests in southern districts causing 2 to 48% damage (Anandhi and Sankarapandian, 2013; Anandhi et al., 2015). An array of sprayable and granular insecticides are recommended against these (Patil et al., 1992), but these have several limitations (Anandhi et al., 2017). Resource poor farmers find problem in chemical spraying due to increased cost of cultivation and possible phytotoxic effects (Sharma, 1993). Current recommendation of soil application with carbofuran 3G @ 30kg/ ha is very expensive (Shekharappa and Bhuti, 2007). Hence, improved IPM approaches are required. Habitat manipulation to enhance the activities of natural enemies aim at minimal or zero insecticide use (Gurr et al., 2004). Prior researches on ecological engineering model in cotton (Muthukrishnan et al., 2015), bhendi (Deepika, 2016) and rice (Chandrasekar, 2016) have demonstrated the use of these. The present study aims to assess the advantages of sorghum- based bund crop, along with other approaches as IPM modules in sorghum along with their validation under rainfed condition in southern region of Tamil Nadu.

The experiment was conducted during 2017 and 2018 at the Agricultural Research Station, Kovilpatti, Tamil Nadu, with eight treatments replicated thrice in a randomized block design (RBD). The K-8 sorghum variety was used in plots of 24.3m² (5.4 x 4.5m) with spacing of 45 x 15 cm. The treatments included neem oil (NO) 3%, neem seed kernel extract (NSKE) 5%, Vitex negundo 10% leaf extract, Ocimum sanctum 10% leaf extract, Aloe vera 10% leaf extract, Calotropis gigantea 10% leaf extract, Datura stramonium 10% leaf extract and an untreated control. Botanicals such as leaves of V. negundo, O. sanctum, A. vera, C. gigantea and D. stramonium were collected and cut into small pieces. The cut leaves were mixed with water at 10% and boiled for 30-50 min and afterward allowed to cool for about 2 hr and was then filtered through muslin cloth (Shakti Khajuria et al., 2015). The extracts were sprayed on the crop on 25, 40 and 55 DAE (days after emergence). A total of 3 sprays at 15 days interval were given using knapsack sprayer @ 500 l spray fluid/ ha. Another experiment was conducted with seven treatments including an untreated check with three replications. Six bund crops viz., coriander, sesamum, cowpea, cluster bean, black gram and bhendi were selected. No chemical pesticides were applied throughout the crop season. The IPM modules consisted of five treatments including farmers practice with four replications were validated.

The details of the treatments are as follows- T₁-Insecticide module with only insecticide application (i. seed treatment with imidacloprid 70 WS @ 3 g/ kg seed; ii. spraying of carbaryl 50WP @ 1 kg/ ha at 28 DAE for shoot fly; iii. Dusting of carbaryl 10D @25 kg/ ha at 60 DAE for stem borer; iv. dusting of carbaryl 10D @25 kg/ ha at 90 DAE for midge), T₂- Ecofriendly module (i. bund cropping sorghum + bhendi; ii. installing fish meal trap up to 30 DAE; iii. releasing of egg parasitoid Trichogramma chilonis at 35 DAE for stem borer; iv. spraying of spinosad 45 % SC @ 75 g ai/ ha at 50 DAE for stem borer; v. spraying neem oil 3% at 60 DAE for midge), T₃- need based integrated module (i. spraying of spinosad 45% SC @ 75 g ai/ ha at 50 DAE for stem borer (stem borer-10% deadheart ETL crossed), ii. releasing of egg parasitoid T. chilonis at 35 DAE for stem borer; iii. spraying neem oil 3% at 60 DAE for midge- (ETL (5/ earhead) crossed), T₄- neem based module with application of only neem products (i. incorporation of neem cake 150 kg/ ha; ii. neem seed kernel extract (5%) at 28 DAE; iii. neem seed kernel extract (5%) at 45 DAE; iv. spraying of neem oil 3% at 60 DAE); and T₅- untreated check. Based on the above modules, the best treatments were assorted and compared with the farmers practice. To validate, large scale field experiments were conducted in farmer’s field with two modules including a farmers practice as a control plot. The IPM modules imposed are as follows: T1- IPM Package (i. timely sowing (41^st standard week); ii. seed treatment with imidacloprid 70 WS @ 3 g/ kg seed; iii. installing fishmeal trap @ 12/ ha up to 30 DAE; iv. bund cropping (sorghum + bhendi); v. releasing egg parasitoid T. chilonis at 35 DAE; vi. Spraying NSKE 5% at 60 DAE); and T2- farmers’ practice compared as check. In case of farmers practice, broadcasting the seeds 15 kg/ ha without any plant protection.

The shoot fly deadheart at 28 days after emergence (%), stem borer deadhearts at 45 days after emergence (%), midge spikelet damage (%) panicle maturation stage were observed in each treatment following protocols of AICRIP, Sorghum, DSR, Hyderabad. The occurrence of predatory coccinellids (grubs and adults) and parasitoids (number/ plant) were recorded, and emergences rate of adult parasitoids were represented as % parasitism. In bund crop and IPM validation, cost benefit ratio was calculated considering additional cost (cost of insecticide and operational charge) and benefit (compared to untreated control) in the respective treatments. Data values in % were arc sine transformed prior to ANOVA and treatment means were compared by Least Significant Difference (LSD) (Gomez and Gomez, 1984). IPM Experiments were subjected to student’s t- test.

Effect of plant products against the major pests of sorghum study was consistent over two years and hence the pooled results are discussed. The deadhearts due to shoot fly and stem borer (%) at 28 and 45 DAE revealed that significantly less values in neem oil 3% (11.01 and 11.44%) and NSKE 5% treated plots (13.58 and 12.40%) as compared to control (50.96 and 41.50%). Maximum incidence of midge spikelet damage rating was of 9-grade in control, followed by Aloe vera 10% leaf extract (6-grade), and the least values were in neem oil 3% and NSKE 5% (3 and 3.33-grade). Significantly more grain yield was obtained with neem oil 3% (1907.67 kg/ ha) and NSKE 5% (1869.55 kg/ ha). Maximum cost benefit (C:B) ratio (1:1.95) was NSKE 5% followed by neem oil 3% treated plots (1:1.70) (Table 1). Prabakaran et al. (2019) observed maximum azadirachtin content in the neem tree populations growing in the southern part of India. Shrinivas and Mudigoudra Shekharappa (2009) and Sable (2009) reported that NSKE (5%) and neem oil (2%) spray in sorghum at 21DAT reduced deadhearts and gave maximum yield; similar results were observed with 3% neem oil (Gautam et al., 2014). The antifeedant properties of neem oil 3%, NSKE with shoot fly had been earlier reported (Zongo et al., 1993; Adane Tesfaye and Asmare Dejan, 2006). About the suitable bund crop, least deadhearts (%) due to shoot fly was observed in sorghum + bhendi (11.52%) and sorghum+ sesamum (13.92%); deadhearts due to stem borer was in sorghum + cowpea (6.11%) and sorghum + bhendi (10.20%); with incidence of midge, spikelet damage rating was the least with sorghum+ cowpea, sorghum+ sesamum and sorghum+ bhendi (2-3 grade).

Larval parasitism on sorghum shoot fly, stem borer, midge and general predators such as coccinellids (Menochilus sexmaculata) and spiders were more with sorghum+ sesamum (28.0% and 14/ plot) and sorghum + bhendi (25.00 % and 15/ plot). Maximum grain yield was obtained from sorghum+ sesamum (2046.00 kg/ ha) followed by sorghum+ bhendi (1815.77 kg/ ha). Maximum C: B ratio (1: 2.25) was also obtained in sorghum+ bhendi followed by sorghum+ sesamum (1: 2.19) (Table 1). Karibasavaraja et al. (2005) reported that sorghum+ coriander, sorghum+ sesamum intercropping resulted in lowest number of deadhearts due to shoot fly. Sorghum+ bhendi best intercropping combination was reported by Degri and Richard (2014) and sorghum + groundnut, sorghum + pegionpea intercropping was suggested by Rana et al. (1998).

Validation of the IPM modules against major pests of sorghum revealed that the deadhearts due to shoot fly and stem borer at 28 and 45 DAE were significantly minimum in insecticide applied module (12.76%) followed by need based integrated module (14.97%) as compared to control (62.08%); similar was the trend in insecticide applied module (7.22) and ecofriendly module (7.30%) as compared to control (42.19%). The least incidence of midge spikelet/ damage rating was observed in need based integrated module and insecticide applied module (3-grade). Grain yield was maximum with insecticide module with only insecticide application (2396.25 kg/ ha) followed by need based integrated module consisting of insecticides, botanicals and natural enemies (2115.75 kg/ ha); however, the maximum C: B ratio (1:1.63) was obtained in ecofriendly module followed by neem based module (1:1.31) (Table 2). The best performing ecofriendly IPM module was reframed as modified IPM module and was conducted in large scale. The results revealed that deadhearts due to shoot fly and stem borer at 28 and 45 DAE get significantly reduced in IPM module (13.02 and 7.61%) as compared to control (45.97 and 36.67%); also lease incidence of midge/ spikelet damage rating was in the integrated module (2.58 grade). Yield was significantly more from IPM module (2700 kg/ ha) with maximum C: B ratio (1:2.27). A fine tuning of advocated sorghum-IPM has proven to maximize the yield generation (Table 2).

Daware and Ambilwade (2014) and Karabhantanal et al, 2018 identified IPM module with different components for management of sorghum pests in India. In the present study, the IPM module validated in large scale including timely sowing (41^st standard week), seed treatment with imidacloprid 70 WS @ 3 g/ kg seed, installing fishmeal trap @ 12/ ha upto 30 DAE; bund cropping (sorghum + bhendi), releasing egg parasitoid, T. chilonis at 35 DAE; followed by spraying NSKE 5% at 60 DAE was found economically prudent to suppress major pests incidence and increased the production. Hence, this module can be recommended as part of an integrated pest control system, since the module recorded minimum pests infestation and increased population of free living natural enemies with highest cost benefit ratio of (1: 2.27) in large scale demonstrations against major pests of sorghum.

DAE=Days after emergence;

Figures in parentheses arc sine transformed value;

^¤¤¤Azadirachtin % in neem oil and NSKE 0.33 and 0.03 % by the test method IS 14300 (1995) - Neem Based EC containing azadirachtin (FAD 1: Pesticides and Pesticides Residue Analysis);

Square root transformation value;

Sorghum grain equivalent yield (SGEY) kg/ha; Cost of inputs based on prevailing market prices; Means followed by different letters significantly different (p=0.05)

DAE=Days after emergence; IPM includes: Timely sowing (41^st standard week); Seed treatment with imidacloprid 70 WS @ 3 g/kg seed; Installing fishmeal trap @ 12/ha upto 30 DAE; Bund cropping sorghum + bhendi; Releasing egg parasitoid, T. chilonis at 35 DAE; Spraying NSKE 5% at 60 DAE

References