POPULATION DYNAMICS, YIELD LOSSES AND MANAGEMENT OF THRIPS, Scirtothrips dorsalis Hood INFESTING CHILLI
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Date
2013-10
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Abstract
Key words: Chilli, thrips, leaf curling, losses, management and residue
The investigation on population dynamics, yield losses and management of thrips, Scirtothrips dorsalis Hood infesting chilli was carried out at two different location i.e. farmer’s field (Village Devlki, Taluka: Vadia, Dist: Amreli) in North Saurashtra Agroclimatic Zone during 2011 and at Junagadh (South Saurashtra Agroclimatic Zone) during 2012.
The population dynamics of thrips, S. dorsalis Hood infesting chilli crop and the leaf curling appeared was studied at different two location (in North Saurashtra Agroclimatic Zone and in South Saurashtra Agroclimatic Zone) during Kharif 2011 and 2012. The results revealed that the thrips infested the chilli crop right from seedling stage to maturity stage of the crop. The thrips infestation commenced in 31st standard week and the pest population multiplied very fast from 33rd to 42nd standard week and reached at peak 84.13/ 3 twig. Thereafter, pest population was decreased. The chilli leaf curling was also appeared with thrips and increased fats from 14 per cent to 81 per cent with increased thrips population. The higher activity of thrips on chilli crop at both the location was found during 41st to 45th standard week. The weather parameters supported high multiplication of the thrips on chilli were maximum temperature 35℃ to 37.1℃ and minimum temperature 18.35℃ to 22.15℃, maximum relative humidity 57.5 per cent to 70 per cent and minimum relative humidity 26 per cent to 31.5 per cent, wind seed 2.65 to 4.35 km/h, bright sun shine hours 7.35 to 9.65 h/day and evaporation rate 5 to 5.6 mm/day with no rain.
The correlation study indicated that increased thrips population on chilli crop was highly positive with maximum temperature, while significantly positive correlation with evaporation rate and bright sunshine hours. However, the correlation of thrips population with minimum relative humidity was highly negative, while significantly negative correlation with maximum relative humidity. Non-significant negative correlation between thrips population and minimum temperature and rainy days was exhibited. Correlation between thrips population and leaf curling severity was existed highly significant.
The relationship of appearance of leaf curling and the thrips infesting chilli was studied by three different angles. The percentage of leaf curling (severity) was
increased with increased number of thrips per plant. The coefficient of correlation between number of thrips and percentage of leaf curling was strongly positive. After the insect were eliminated by the insecticidal spraying, the growth of plants was normal and without curling within 20 day. While the plant kept as control (untreated) were continued with thrips and pronounced leaf curling recorded. The cell sap of leaves having severe and typical symptoms of leaf curling was inoculated on the healthy tender leaves of potted healthy plants. Leaf curling symptoms not produced in the sap inoculated plants (protected). This result indicated that insect born virus was not responsible for producing the leaf curling in chilli.
The experiments on qualitative and quantitative losses caused by thrips, S. dorsalis infesting chilli were conducted at two different location (in North Saurashtra Agroclimatic Zone and South Saurashtra Agroclimatic Zone) during Kharif 2011 and 2012. The result revealed that 62.58 per cent leaf curling, 26.34 per cent plant height, 28.50 per cent branches, 33.39 per cent length and 11.01 per cent width of fruit (green chilli) and 62.83 per cent length and 64.04 per cent width of leaf were reduced due to infestation of the thrips in chilli. Further quality of green chilli i.e. appearance, shape, luster of green chilli was also detoriated.
The quantitative (yield of green chilli) losses was ranged 11333 kg/ha (289.77%) to 10911 kg/ha (299.39%) with an average 11122 kg/ha (294.41%). The avoidable loss was 74.34 per cent to 74.96 per cent with average of 74.65 per cent.
Bioefficacy of the twelve insecticides was evaluated against thrips, S. dorsalis infesting chilli on farmer’s field. Three application of the insecticides was given at fifteen day interval. The result revealed that significantly the highest reduction in thrips population (7.33 thrips/3 twig) and leaf curling (13.29 per cent) was recorded on chilli crop treated with spinosad 0.009 per cent followed by profenophos + cypermethrin 0.044 per cent, abamectin 0.003 per cent, imidacloprid 0.005 per cent, profenophos 0.05 per cent, acetamiprid 0.008 per cent, diafenthiuron 0.05 per cent and indoxacarb 0.0145 per cent. The maximum thrips population 52.22/3 twig and degree of leaf curling 56.97 per cent was recorded on untreated plants (control). The significantly maximum yield (15278 kg/ha) of green chilli with 229.34 per cent increased over control was recorded from the crop treated with spinosad 0.009 per cent followed by profenophos + cypermethrin 0.044 per cent, abamectin 0.003 per cent and imidacloprid 0.005 per cent. The highest monitoring net return of ` 212780/ha was also recorded from spinosad 0.009 per cent followed by profenophos + cypermethrin 0.044 per cent (` 182220/ha), abamectin 0.003 per cent (` 161660/ha), imidacloprid 0.005 per cent (` 160000/ha), acetamiprid 0.008 per cent (` 145000/ha) and profenophos 0.05 per cent (` 140560/ha).
The six insecticidal spray schedule having three to eight insecticidal applications at 30, 20, 15, 12, 10 and 8 days interval were evaluated against chilli thrips. The schedule 6 having eight insecticidal applications at eight day interval starting from 40 day after transplanting was found most effective against chilli thrips and leaf curling. The maximum yield 10875 kg/ha with the highest net monitoring return was also received by the schedule 6. The insecticides applied in schedule 6 were (i) Polytrin C (profenophos 40% + cypermethrin 4%) 0.044 per cent, (ii) abamectin 0.003 per cent, (iii) imidacloprid 0.005 per cent, (iv) spinosad 0.009 per cent, (v) Polytrin C (profenophos 40% + cypermethrin 4%) 0.044 per cent, (vi) acetamiprid 0.008 per cent, (vii) spinosad 0.009 per cent and (viii) imidacloprid 0.005 per cent.
The residue of imidacloprid 0.005 per cent, abamectin 0.003 per cent and cypermethrin 0.004 per cent (Polytrin C 0.044%), spinosad 0.009 per cent and profenophos 0.04 per cent was below maximum residue limit (MRL). The residue of these insecticides in/on green chilli was below its maximum residue limit (MRL). But the residue of acetamiprid 0.008 per cent (0.346 mg/kg) was slightly above the maximum residue limit (0.20).
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CHILLI