Effect of biorationals and weeding on management of whitefly (Bemisia tabaci) in cotton
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Date
2019
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CCSHAU
Abstract
The present study was carried out during Kharif 2018 at Biocontrol Laboratory and Research Farm, Cotton Research Station, Sirsa. Mean adult population (adults/leaf) peaked twice during the study i.e. in 29th (8.01 and 8.82/ leaf) and 35th SMW (8.96 and 10.89 / leaf) whereas, whitefly nymphs peaked in 34th SMW (20.12 and 23.21/leaf) in non-weedy and weedy habitat respectively. White fly population (nymphs and adult) had a non-significant positive correlation with temperature and relative humidity. Adult population in non-weedy habitat was significantly negatively correlated with rainfall (r = -0.502) and wind speed (r = -0.515) whereas nymphal population showed non-significant negative correlation. Regression analysis revealed that influence of weather parameters was high and significant on whitefly adults (R2=0.86) and nymphal (R2=0.57) population. Maximum mortality of adults and nymphs (among biorationals) after 1st spray in non-weedy (66.76 and 60.65 per cent mean mortality in adult and nymphal population, respectively) as well as weedy habitat (56.77 and 55.54 per cent mean mortality in adult and nymphal population, respectively) was observerd in nimbicidine 300 ppm treatment. Efficacy Nimbicidine 300 ppm on whitefly adults was followed by Verticillium lecanii, Beauveria bassiana and Metarhizium anisopliae and after 2nd spray the same trend was observed. Among the entomopathogenic fungi, V. lecanii was found more effective against whitefly adults whereas M. anisopliae caused higher mortality in nymphal population. Parasitisation of whitefly nymphs by aphelenid wasp, Encarsia spp. ranged from 2.63 to 28.51 per cent in non-weedy habitat and from 3.85 to 35.75 per cent in weedy habitat and peak parasitization was observed in 41st SMW in both habitats. Parasitization showed non-significant negative and positive correlation with temperature and relative humidity, respectively. Parasitization was at weak correlation with rainfall. Weather parameters cumulatively caused 74.0 and 66.0 per cent change in nymphal parasitization in non-weedy and weedy habitats, respectively. All biorationals were found safe for Encarsia sp. Parasitization, however V. lecanii showed highest and Nimbecidine 300 ppm lowest mean parasitisation after both spray. Highest cotton yield (kg/acre) among the biorationals in weedy as well as non-weedy, was obtained with Nimbecidine 300 ppm treatment (768.26 and 642.00 kg/ acre in weedy and non-weedy habitat respectively) followed by V. lecanii (741.02 and 621.28 kg/acre) lowest yield was obtained in control plots (603.16 and 536.24 kg/acre).
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