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Subject: Entomology × Author: Ramandeep Kaur × End date: 2020 ×
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    Estimation of losses and determination of economic threshold level of Thrips tabaci Lindeman on cotton
    (Punjab Agricultural University, Ludhiana, 2014) Ramandeep Kaur; Kular, J.S.
    Experiments regarding estimation of losses, determination of economic threshold level and population dynamics of thrips, Thrips tabaci Lindeman on cotton were carried out during the year 2013 at Punjab Agricultural University, Ludhiana. For the estimation of losses, seven initial levels viz. 0, 50, 100, 150, 200, 250 and 300 thrips per plant were released on the plants covered with muslin cloth cages (1x1x2m). Effect of different levels of T. tabaci population on different morphological characteristics of plants i.e. number of leaves, number of damaged leaves, leaf size, number of sympods, number of monopods, number of squares, number of flowers, number of bolls, number of pickable bolls, seed cotton yield and root size/plant and internodal length and plant height were studied. All the plant characters tended to decrease with increasing population level except the number of damaged leaves which kept on increasing with increasing population level. The effect of different levels of thrips population on all morphological characters was significant except the number of monopods. Yield losses of 2.4, 4.62, 5.24, 7.13, 9.44 and 11.8 per cent were observed in 50, 100, 150, 200, 250 and 300 thrips per plant, respectively. For the determination of economic threshold level, six population levels taken for initiating sprays were 10, 15, 20, 25, 30 and 35 thrips/ leaf. Economic threshold level was calculated to be 10 thrips (nymphs and adults) per leaf or appearance of I injury grade i.e. minor appearance of silver streaks around midrib and veins of leaves. For the study of population dynamics, population was recorded from three leaves (each from top, middle and bottom canopy) of ten randomly selected plants at weekly interval and correlation coefficient was worked out with abiotic factors such as temperature, relative humidity and rainfall. Correlation studies showed negative and significant correlation with mean RH (r= -0.71) morning RH (r= -0.81) and evening RH (r= -0.54), positive and significant correlation with mean temperature (r= 0.77), maximum temperature (r= 0.79) and minimum temperature (r= 0.58) and negative non significant correlation with rainfall (r= -0.21).