Field efficacy of biocapsules of entomopathogenic fungi for the management of vegetable pests

Abstract

The study entitled “Field efficacy of biocapsules of entomopathogenic fungi for the management of vegetable pests” was conducted at the Biocontrol Laboratory for Crop Pest Management, Department of Agricultural Entomology, College of Agriculture, Vellayani, Thiruvananthapuram, during the year 2018-2021. The objective of the study was to evaluate the efficacy of biocapsules of Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, Lecanicillium lecanii (Zimmermann) Zare and Gams and Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno for the management of major groups of vegetable pests. The study also intended to standardize the dose of biocapsules in managing amaranthus leaf webber Spoladea (Hymenia) recurvalis F., okra shoot and fruit borer Earias vittella F. and cowpea aphid Aphis craccivora Koch. The biocapsules of fungi were formulated at a higher spore load of 1010 with HPMC coating and chitosan as carrier, following the protocol developed by Remya and Reji (2019). In the first field experiment to evaluate the efficacy of biocapsules in managing defoliators in amaranthus, it was revealed that, Metarhizium and Beauveria capsules @ 3 L-1 sprayed twice (at weekly intervals) was effective causing 83.69 and 69.97 per cent reduction in population of S. recurvalis respectively. Lower doses of 2 and 1 capsules L -1 were less effective causing, 47.39 to 66.5 per cent reduction in larval population. Spraying spore suspensions of these fungi @ 108 mL-1 resulted in 91.27 to 100 per cent reduction, while in flubendiamide 39.35 SC, it was 89.84 per cent. Treatment with Metarhizium and Beauveria capsules did not affect the natural enemy population significantly, the mean population being 2.33 to 3.67 plant-1 . The corresponding population was 1.44 in flubendiamide 39.5 SC and 3.67 in untreated control. The yield recorded in the plots treated with Metarhizium and Beauveria capsules @ 3 L -1 was high (2.67 and 2.30 kg plot-1 ) when compared to that in untreated plot 0.80 kg plot-1 . Results of the second experiment to evaluate the efficacy of biocapsules in managing fruit and shoot borer E. vittella in okra concluded that, Beauveria capsule @ 3 L -1 and Metarhizium capsule @ 3 L-1 were equally effective when sprayed at weekly intervals leading to 84.96 and 79.64 per cent reduction in the shoot damage respectively. The percentage reduction in shoot damage was only 65.32 to 73.86 per cent reduction in lower doses of capsules. In plots treated with spore suspensions, the mean shoot damage recorded was 90 to 95 per cent. Percentage reduction in chlorantraniliprole 18.5 SC was 90.71. Considering the fruit damage, Metarhizium capsule @ 3 L-1 was found to be the best treatment causing 100 per cent reduction in damage caused by E. vittella, while it was 89.75 per cent with Beauveria capsule@ 3 L -1 . Reduction in fruit damage ranged from 67.82 to 82.81 per cent in the lower doses of capsules. Highest reduction in the fruit damage observed with spore suspensions of Beauveria and Metarhizium @ 108 mL-1 (93.16 and 100 per cent, respectively). Similar results were obtained in the case of okra leaf roller, Metarhizium @ 2 L-1 and Beauveria capsule @ 3 L -1 were found to be the best treatment causing 96.38 and 85.80 per cent reduction in population of Sylepta derogata F., while it was 80.23 per cent with Metarhizium capsule @ 3 L-1 . Reduction in population ranged from 41.35 - 68.72 per cent in the lower doses of capsules. Highest reduction in the population of S. derogata observed with spore suspensions of Beauveria and Metarhizium @ 108 mL-1 (100 per cent). Percentage reduction in chlorantraniliprole 18.5 % SC was 93.41. Treatment with biocapsules capsules did not cause any adverse affect on natural enemy population, in okra field. The yield obtained from different treatments did not vary significantly. Third experiment in cowpea field revealed that, foliar application of L. saksenae capsule @ 3 L -1 and L. lecanii capsule @ 3 L-1 were equally effective to A. craccivora when sprayed twice (at weekly intervals) causing 94.38 and 92.28 per cent reduction in the population respectively. Reduction in population noted was 57.54 to 63.96 per cent with lower dose @ 2 capsules L-1 while it was least with single capsule treatment (37.51 to 44.73 per cent). The spore suspensions were more effective resulted than the lower doses (78.73 - 83.53 per cent reduction). The chemical check thiamethoxam 25 WG recorded 95.79 per cent reduction in population. Biocapsule treatment did not affect natural enemy population significantly. The yield recorded in the plots with L. saksenae capsules @ 2 and 3 L-1 was high (1.85 and 1.56 kg plot-1 ) when compared to other treated plots and untreated plot (1- 1.45 kg plot-1 ). Therefore, it is concluded that biocapsules of Metarhizium and Beauveria, can effectively manage defoliators in amaranthus and borers in okra and those of L. lecanii and L. saksenae can be recommended for pea aphids, without affecting the natural enemies and yield significantly.