Bio-efficacy of Different Insecticides Against Thrips ( Scirtothrips dorsalis Hood ) in Green Gram

Investigation on the management of thrips, Scirtothrips dorsalis Hood infesting green gram was carried out under field condition during 2017 at Pulse Research Station, Junagadh Agricultural University, Junagadh, India. For the management of thrips, different combinations of seed treatments viz., imidacloprid 30.5 SC @ 0.12%, clothianidin 50 WDG @ 0.20% and thiamethoxam 25 WG @ 0.01% and foliar application of insecticides profenophos 40% + cypermethrin 4% 44 EC @ 0.044%, spinosad 45 SC @ 0.0135% and flonicamid 50 WG @ 0.015% were evaluated against the pest. Based on pooled over periods, seed treatment of thiamethoxam 25 WG @ 0.10% and insecticidal spray of spinosad 45 SC @ 0.0135% was found most effective for the control of thrips. The highest (1066 kg /ha) seed yield was gained from the plots treated with thiamethoxam 25 WG @ 0.10% + spinosad 45 SC @ 0.0135% followed by imidacloprid 30.5 SC @ 0.12% + spinosad 45 SC @ 0.0135% (1025). Maximum yield loss can be avoided with spray application of thiamethoxam 25 WG @ 0.10% + spinosad 45 SC @ 0.0135% (90.64%) followed by imidacloprid 30.5 SC @ 0.12% + spinosad 45 SC @ 0.0135% (83.16%) as compared to control. Article History Received: 30 June 2018 Accepted: 10 September 2018


Introduction
Among the different pulses, green gram, Vigna radiata (Linnaeus) Wilczek is an ancient and well known leguminous crop of Asia, belonging to Leguminosae family.It is one of the thirteen food legumes grown as third most important pulse crop of India after chickpea and pigeonpea.In India, area covered by pulses is 25.26 million hectares (mha) with production of 16.47 metric tones (mt) and productivity of 665 kg /ha. 1 About 70 per cent of the world's total production of green gram is produces in India whereas, it is cultivated annually in an area of 3.83 mha with total production and average productivity of 1.603 mt and 418 kg /ha, respectively. 2f late in India, the average productivity of green gram crop has rather remained static due to several reasons viz., lack of suitable seed production techniques, cultural practices, inefficient harvest and post-harvest operations, improper storage management practices, etc. Apart from these, green gram seed is bound to show rapid and greater losses both quantitatively and qualitatively due to attack of several insect pests at both pre and postharvest stages.Annually 2.0 to 2.4 mt of pulses with approximately monetary value of Rs.6000 corers are lost due to damage caused by insect pest. 3ung bean is being reported with nearly 60 insect's species. 4Among the different sucking insect pests of green gram, thrips is the major problematic pest in the initial growth period of the crop.The pest suck the cell sap continuously, which leads to drying up of the small tender leaves and thus hinders the vegetative growth and development of green gram.In the situation of global climate change, living organisms are changing their living habitat as well as style, which directly affect their span of life.A dominant animal, insect, have capacity to change their behavior and habitat with the changing of the environment and so, the study was carried out to see the impact of changing pattern in abiotic factors on green gram thrips.Several chemical pesticides have been recommended for combating thrips.However, problems like residues in seeds and environmental contamination are the result of injudicious use of these chemical pesticides.Such reliance on insecticides has created many problems such as very frequent application of insecticides, excessive residues in the produce, which are the concerns of general consumer health and the environment, pesticide resistance, trade implications, poisoning, hazards to non-target organisms and increased production costs etc.Among the several avenues to overcome the insecticidal resistance problem and as this pest continued to attack the primary stage of the crop.Therefore, there is a need to check the effects of seed treatment along with foliar application of insecticides were one of the important considerations.

Materials and Methods
The experiment was laid out in a Randomized Complete Block Design (RCBD) with factorial concept with three replications keeping plot size of 4.00 m x 2.70 m during summer 2017 at Pulse Research Station, Junagadh Agricultural University, Junagadh.Green gram variety GM 4 was sown at a spacing of 45 cm x 10 cm in February, 2017.All agronomic practices were adopted as per the recommendation in vogue.The seed treatment was done three hours before sowing with three different insecticides viz., imidacloprid 30.5 SC @ 0.12%, clothianidin 50 WDG @ 0.20% and thiamethoxam 25 WG @ 0.01% and spraying was done using knapsack sprayer of three different insecticides viz., profenophos 40% + cypermethrin 4% 44 EC @ 0.044%, spinosad 45 SC @ 0.0135% and flonicamid 50 WG @ 0.015% for the control of thrips.As the population of thrips was heavy starting after the week of germination, the immediate spray was carried out to check the population.Second spray was carried out at 12 days after the first spray to combat the pest.The observations on thrips were recorded visually from five randomly selected and tagged plants from its upper, middle and lower leaves.Observations on thrips population were recorded at 1, 3, 5, 7 and 9 days after each spray.With a view to evaluate the effect of different pesticides on the green gram yield, crop was harvested from each net plot.The harvested yield was weighted and converted on hectare basis.The percentage increase in yield over control was calculated by using the following formula. 5rcentage increase over control = 100 x T-C C Where, T= Yield of respective treatment (kg/ha) C= Yield of control (kg/ha)

Result
The data on mean thrips count after seed treatment and two applications of insecticides pooled over spray were presented in table 1 and 2. The periodical data showing the effects of seed treatment and insecticidal spray on infestation to green gram due to thrips on one, three, five, seven and nine days after spray (DAS) was also presented.The bio-efficacy of various insecticides had been adjudged based on pooled over spray.
The data on mean thrips count of pooled over spray presented in table 1 revealed that among three different seed treatment, thiamethoxam 0.10% had lowest thrips count (0.45 thrips /leaf).Next best treatment was imidacloprid 0.12% (0.51) followed by clothianidin 0.20% (0.59) at one day after spray (DAS).On third, fifth, seventh and ninth DAS results were found to be non-significant.As the crop was sown during February, 2017, this kind of result may be due to lower efficacy of seed treatment after 27 days of sowing.
The data on mean thrips count of pooled over spray presented in table 1 revealed that among sprayed insecticides, spinosad 0.0135% (0.28) was found with lowest thrips count followed by flonicamid 0.015% (0.52) and profenophos + cypermethrin 0.044% (0.82) on first DAS.While on third DAS, spinosad 0.0135% was found best followed by flonicamid 0.015%, this was at par with profenophos + cypermethrin 0.044%.Similar pattern was observed for spinosad 0.0135% < flonicamid 0.015% < profenophos + cypermethrin 0.044% on fifth and seventh DAS i.e., 0.55 < 0.72 < 1.13 and 1.54 < 1.85 < 2.35, respectively.At ninth DAS spinosad 0.0135% was found at par with flonicamid 0.015% followed by profenophos + cypermethrin 0.044%.The data in table 2 showed seed treatment with insecticidal spray interaction effect (S x I) was found to be non-significant on first, third and ninth DAS while, at 5 and 7 DAS the interaction effect was found to be significant at 5% of probability.

Discussion
It was observed that green gram thrips, S. dorsalis can be effectively managed by seed treatments of thiamethoxam and imidacloprid up to 27 days after sowing of green gram crop.Spinosad and flonicamid exhibited satisfactory protection against thrips throughout the infestation.The obtained results are in conformity with the submission of the earlier workers as 6 proved effectiveness against thrips as thiamethoxam @ 4.3 g /kg and 8.6 g /kg up to 30 days of germination in green gram.Similarly, 7 found thiomethoxam 0.03 kg a.i./ha as most promising treatment against thrips followed by spinosad 0.07 kg a.i./ha.In onion, spinosad 45 SC @ 0.0135% was found best insecticide against thrips. 8According to, 9 imidacloprid @ 200 g/acre was the most effective insecticide, while 10 found that the combination of imidacloprid as a seed treatment with foliar spray of acephate gave the best result for the control of thrips in mung bean.Thiamethoxam was found most effective in managing the pest. 11pinosad found to be superior for the management of thrips population in asparagus bean. 12Green gram is affected by thrips species viz., Megalurothrips distalis, Thrips tabaci, Scirtothrips dorsalis etc.However, literature related to management of Scirtothrips dorsalis infesting green gram is scanty.Hence, in the present investigation the results are nearer to the earlier findings but not the same.

Table 1 : Effects of seed treatment along with foliar application of insecticides against thrips (pooled over sprays)
3. Treatment mean with letter(s) in common are not significant at 5 % level of significance within a column.