Efficacy of different insecticides on pod and grain damage due to pod borer complex (Maruca testulalis, Helicoverpa armigera and Exelastis atomosa) in pigeonpea during kharif season 2020-21

Introduction

Pigeonpea (Cajanus cajan) is one of the most important pulse crops cultivated in India and plays a vital role in nutritional security due to its high protein content (Sharma, 2005) [10] . However, the productivity of pigeonpea is severely constrained by several insect pests, among which the pod borer complex is considered the most destructive (Lal and Yadav, 1998) [4] . The major pod borers attacking pigeonpea include Helicoverpa armigera (gram pod borer), Maruca testulalis (spotted pod borer), and Exelastis atomosa (plume moth) (Reed et al., 1987) [9] . These pests damage flowers, pods, and developing grains, causing substantial quantitative and qualitative yield losses. Yield losses due to pod borers may range from 30-80% depending upon pest incidence and environmental conditions (Lateef and Reed, 1990) [5] . Conventional insecticides have been widely used for management; however, indiscriminate use has resulted in resistance development, resurgence, and environmental concerns (Kranthi et al., 2002) [3] . Therefore, evaluation of newer insecticidal molecules and bio-pesticides is essential for sustainable pest management (Sharma, 2005) [10] . The present investigation was undertaken to evaluate the efficacy of different insecticides against pod and grain damage caused by pod borer complex in pigeonpea during the kharif season of 2020-21.

Materials and Methods

Experimental Site

The field experiment was conducted during the kharif season of 2020-21 at the experimental farm under natural infestation conditions of pod borer complex.

Observations Recorded

The following observations were recorded:

 Total number of pods per plant  Mean pod damage (%)  Reduction in pod damage over control (%)  Total number of grains per plant  Mean grain damage (%)  Reduction in grain damage over control (%)  Grain yield (q/ha)  Percent increase in yield over control

The recorded data were statistically analysed. Percent data were transformed using square root transformation before analysis (Gomez and Gomez, 1984) [2] .

Results and Discussion Effect on Pod Damage

The data revealed significant differences among treatments regarding pod damage caused by pod borer complex. Among all treatments, T1 (flubendiamide followed by chlorantraniliprole) recorded the lowest pod damage across all varieties. Pod damage ranged from 12.41% to 13.52%, with reduction over control ranging from 74.48% to 78.53%. The highest number of pods per plant was also recorded under this treatment. Similar findings were reported by Babariya et al. (2010) [1] , who observed effective suppression of pod borer infestation with newer insecticidal molecules. Emamectin benzoate (T3) was the next effective treatment, recording pod damage between 16.41% and 17.88%, with pod damage reduction ranging from 66.25% to 70.26%. The findings are in agreement with those of Prakash et al. (2021) [7] , who reported superior efficacy of Emamectin benzoate against pod borers in pigeonpea.

The bio-pesticide treatment, Bacillus thuringiensis (T2), showed comparatively lower efficacy, with pod damage ranging from 25.21% to 34.57%. Similar moderate effectiveness of B. thuringiensis against lepidopteran borers has been documented by Singh and Verma (2006) [11] . Untreated control plots exhibited maximum pod damage (48.62-60.12%), indicating severe infestation under unprotected conditions. The superior performance of T1 may be attributed to the strong stomach and contact action of diamide insecticides against lepidopteran borers (Raghvani and Poshiya, 2006) [8] .

Effect on Grain Damage

Significant reduction in grain damage was observed in insecticide-treated plots compared with control. T1 recorded minimum grain damage ranging from 6.89% to 7.10%, with grain damage reduction of 75.50-77.90% over control. The treatment also produced the highest number of grains per plant. These results corroborate the findings of Yelshetty et al. (1999) [12] , who reported effective reduction of grain damage in pigeonpea through newer insecticides. T3 recorded grain damage between 9.29% and 9.50%, while T2 recorded comparatively higher grain damage (16.80-18.48%). Similar observations were made by Mehla (1990) [6] , who found Emamectin and related insecticides effective in minimizing grain damage caused by H. armigera. Control plots recorded maximum grain damage ranging from 28.98% to 31.19%, confirming the destructive nature of pod borer complex under untreated conditions.

These findings clearly indicate that newer insecticidal molecules effectively minimized larval feeding and protected developing grains (Sharma, 2005) [10] .

Effect on Grain Yield

All insecticidal treatments significantly increased grain yield over untreated control. The highest grain yield was recorded in T1, ranging from 19.49 to 21.69 q/ha, with yield increase over control ranging from 45.12% to 54.82%. Similar enhancement in yield due to effective pod borer management has also been reported by Babariya et al. (2010) [1] . Emamectin benzoate (T3) produced grain yields ranging from 18.10 to 19.52 q/ha, which was significantly higher than untreated control. The results are supported by Prakash et al. (2021) [7] .

Bacillus thuringiensis recorded moderate yields ranging from 16.35 to 17.69 q/ha. The untreated control recorded the lowest grain yield (14.43-16.01 q/ha), mainly due to higher pod and grain damage caused by the pest complex.

The increase in yield under insecticidal treatments was directly associated with reduced pod and grain damage (Lateef and Reed, 1990) [5] .

Conclusion

The study revealed that all insecticidal treatments significantly reduced pod and grain damage caused by the pod borer complex in pigeonpea compared to untreated control. Among the treatments, sequential application of flubendiamide followed by chlorantraniliprole (T1) proved most effective by recording minimum pod and grain damage and maximum grain yield. Emamectin benzoate (T3) was the second-best treatment, while Bacillus thuringiensis (T2) provided moderate control. The untreated control showed maximum infestation and lowest yield. Therefore, flubendiamide followed by chlorantraniliprole can be recommended for effective management of pod borers in pigeonpea during kharif season.

References

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