Bioefficacy of new molecule fipronil 5% SC against sucking pest complex in Bt cotton

Abstract: : The efficacy of fipronil 5% SC @ 800 g/ha, fipronil 40% + imidacloprid 200 SL @ 200 ml/ha, acetamiprid 20SP@ 100 g/ha and triazophos 40 EC @ 1500 ml/ha (standard checks) was evaluated against sucking pests of cotton, at ARS,Dharwad. All the insecticides were found to give ef fective control of leafhoppers, aphids and thrips. Fipronil 5% SC @ 800g/ ha registered least number of thrips (8.47 / 3 leaves) and found to be on par with acetamiprid 20 SP @ 100 g/ha, (7.80 /3leaves). Fipronil 40% + imidacloprid 40% - 80 WG and was next best and imidacloprid 200 SL. Significantly highest seedcotton yield of 27.23 q/ha (2007) and 27.50 q/ha (2008) was harvested with higher dosage of fipronil 5% SC @ 800 g/harespectively proving them to be on par with acetamiprid 20 SP.Key words : Fipronil 5% SC, acetamiprid 20 SP , Fipronil 40% + imidacloprid 200SL, sucking pest complex IntroductionCotton is an important commercial crop unanimouslydesignated as king of fibre crops and is prone to pest attack atvarious stages of crop growth. Cotton production system in thecountry illustrates well, the ecological and environmentalproblems associated with intensive use of synthetic insecticides.The introduction of synthetic pyrethriods, though broughtdesirable control of bollworms, resulted in resurgence of suckingpests viz, aphids, leafhoppers, thrips and whitefly that havealso been reported in cotton system due to excessive use ofsynthetic pyrethriods (Ajri et al ., 1986, Patil et al ., 1986). Manyinsect pests are of economic importance and do causeconsiderable yield loss 57-80 per cent. Cotton growers in Indiarely mainly on synthetic pesticides to combat sucking pests.Continuous and indiscriminate use of insecticides resulted inresistance development to these insecticides which reflectedon the reliability of ef ficacy of these insecticides. To overcomethese associated problems, discovery of novel molecules areessential. New molecules are effective at lower doses and haveleast exposure in the environment.Fipronil (Regent®) belongs to a new class ofinsecticides fiproles and was found to be efficient compared topyrethroid, OP and carbomate insecticides (Patil et al ., 2004). Inthe present investigation, fipronil has been evaluated for itseffectiveness against sucking pests of cotton as a solecompound as well as a combination of product with imidacloprid200SL.Material and methodsField experiments were carried out under All India Co-ordinated Cotton Improvement Project (AICCIP) during kharif2007 and 2008 at ARS Dharwad farm in medium deep black cottonsoil under rainfed conditions. The experiments were configuredwith eight treatments which were replicated four times. Cottonhybrid RCH-2Bt was sown in a plot size of 5.4x5.4 sq.m with aspacing of 90x60 cm. The crop was raised following all standardagronomical practices. The treatments were imposed as and whensucking pests crossed ETL viz, 2 nymphs of jassids, or 10nymphs/adults of thrips or aphids per leaf.The populations of sucking pests viz., thrips, aphidsand leafhoppers were recorded from randomly selected tenplants. Observations were subjected to statistical analysis toasses the impact of new molecules on pest incidence. Seedcotton yield was harvested from each treatment and finallyexpressed in quintal/ha.Results and discussionA day before the imposition of treatment, populationof sucking pest was quite uniform and above the economicthreshold level. Five days after the spray , thrip, leafhopper andaphid populations reduced considerably and registered 7.91,1.40 and 5.64 per three leaves respectively in the plots sprayedwith fipronil 5% SC @ 800g/ha which was statistically on parwith standard check acetamiprid 20SP @ 100 ml/ha (7.95, 1.18and 6.00/3 leaves). Significantly higher seed cotton yield of27.23q/ha was obtained from fipronil 5% SC @ 800 g/ha andcomparable to acetamiprid 20 SP , the standard check (27.60 q/ha) and imidacloprid 200SL (26.70 q/ha). On the contrary theuntreated check registered significantly lowest seed cotton yield(21.25 q/ha). The next best treatment was fipronil 40% +Imidacloprid 40% - 80 WG and statisticacly on par with anotherstandard check imidacloprid 200 SL (Table 1).During 2008-09 also, prior to the application ofinsecticides, population of all sucking pests complex was quiteuniform and also above ETL (Table 2). However , fipronil 5% SC@ 800 g/ ha registered significantly least number of thrips,leafhopper and aphids (9.03, 1.85 and 1.27 / 3 leaves respectively)and was found to be equally effective as that of standard check,acetamiprid 20 SP (7.66, 1.65 and 1.15 /3 leaves) (T able 2). Theseed cotton yield was significantly highest in fipronil 5 SC(27.50q/ha) and acetamiprid 20SP (27.65 q/ha) sprayed plots bothbeing statistically on par . The combination product of fipronil +imidacloprid could also give better yields (25.26 q/ha).Pooled observations of 2007-08 and 2008-09 revealedthat significantly lower thrip, leafhopper and aphid populationswere noticed in fipronil 5% SC (Regent®) @ 800 g/ha treatment(8.47, 1.62 and 3.45 / 3 leaves, respectively which was found tobe quite effective and par with standard check, acetamiprid (Pride20SP®) @ 100 g/ha (7.80, 1.21 and 3.57 / 3 leaves, respectively(Table 3).