©Haramaya University, 2021 ISSN 1993-8195 (Online), ISSN 1992-0407(Print) East African Journal of Sciences (2021) Volume 15 (1) 41-50 Licensed under a Creative Commons *Corresponding Author: zalemu56@gmail.com Attribution-NonCommercial 4.0 International License. Sequential Application of Various Insecticides for the Management of Cotton Bollworm (Hubner) Helicoverpa armigera (Lepidoptera: Noctuidae) in Cotton Production Zemedkun Alemu 1*, Ferdu Azerefegne 2, and Geremew Terefe 3 1Werer Agricultural Research Center, EIAR, P.O. Box 2003, Addis Ababa, Ethiopia 2College of Agriculture, Hawassa University, P.O. Box 770, Hawassa, Ethiopia 3Sesame Business Network Ethiopia Abstract Background: Cotton bollworm (Hubner) (Helicoverpa armigera) (Lepidoptera: Noctuidae) is a major constraint to cotton production and productivity in Ethiopia. Objective: To determine the best spray sequence of various insecticides as a strategy of resistance management of the pest. Materials and Methods: Field experiments were conducted during the 2017 and 2018 main cropping season at Werer Agricultural Research Center. Eight different insecticides (chlorantraniliprole, deltamethrin, chlorfenapyr, lufenuron+profenofos, chlorpyriphos, lambda- cyhalothrin, profenofos, and alphacypermethrin) belonging to five major insecticide classes were systematically arranged in six treatments and three spraying sequences along with a control treatment. The experiment was laid out as a Randomized Complete Block Design and replicated four times per treatment. Data were collected on bollworm population, damaged squares, flowers, and bolls at pre and post insecticide application, boll number per plant, and seed cotton yield. Using the modified Abbott’s formula, the percent efficacy was computed. Results: Significant differences (P<0.05) were observed among the treatments for post spray larvae count, damaged squares, and boll counts in the 2017 and 2018 cropping seasons. Sequential and rotational application of a cocktail of the insecticides, namely, chlorantraniliprole, chlorfenapyr, profenofos, and chlorfenapyr, chlorantraniliprole, lufenuron+profenofos resulted in the best control with 81.8% and 76.4% of H. armigera larvae controlling efficacy. The lowest average cotton boll number (9.69/plant) and cotton yields (2.24 ton/ha) were obtained from the unsprayed treatment. Conclusion: Applying the insecticides in sequence increased seed cotton yield by 36.2% and 33.9% compared to the yields obtained from the unsprayed plots. The results imply that rotational use of insecticides with different modes of action is the best strategy to control the pest. Keywords: Bolls; Bollworm; Flowers; Mode of action; Pyrethroids; Squares; Yield 1. Introduction In Ethiopia, cotton is one of the most widely cultivated crops both by small and large-scale cotton producers. Presently, production of the cotton crop has become an attractive trade for foreign and local investors which could help the country in terms of providing job opportunities and as a source of foreign exchange earnings (Belay, 2012 cited by EIAR, 2016). However, the pest spectrum of cotton is quite complex among which insect pest problem has become the major one. A total of seventy species of insects and mites have been known to attack cotton at different growth stages in Ethiopia (Ermias et al., 2009) out of which bollworm complex (Helicoverpa armigera, Pectinophora gossypiella, Diparopsis watersi, and Earias spp) is a great menace. Cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is a polyphagous insect damaging diverse crops, such as beans, chickpea, peas, sorghum, cotton, tomato, pepper, sunflower, safflower, flax, and niger seed (Tsedeke Abate, 1982; Waktole Sori, 1996). In Ethiopia, bollworm complexes cause 36–60% yield losses among which H. armigera is a major culprit (Tsedeke Abate, 1982; Waktole Sori, 1996; Geremew Terefe and Ermias Shonga, 2006). All parts of the cotton plant are vulnerable to attack by the pest. The larva feeds on cotton young leaves, squares, flower buds, flowers, and bolls (Geremew and Ermias, 2006; Deguine et al., 2008). In China, cotton bollworms caused about 50– 60% yield reduction each year from 1980–1990 on cotton (Xiao et al., 2002). Cotton pest management is the most important task in the total production cost of cotton in most years. Cotton farms can lose the whole production when correct pest managements are not taken. Among production control costs, 43 % is spent on pesticide purchase, and 33 % on weed control efforts (EIAR, 2016). In Ethiopia, for decades, a wide range of insecticides have been used for the control of cotton insect and mite pests, particularly Cotton bollworm (Ermias Shonga et al., 2009). Control of pests with insecticides from a single chemistry group is mailto:zalemu56@gmail.com Zemedkun et al. East African Journal of Sciences Volume 15 (1) 41-50 42 common in most cotton farms and such a practice for an extended period results in the development of resistance as in the case of lambda-cyhalothrin for Cotton bollworm species at Dubti (Germew Terefe, 2004), dimethoate for aphid species at the Middle Awash (IAR, 1990), and carbamate group (carbosulfan, furathiocarb and pirimicarb) for aphid species resistance at Arbaminch, Dubti and Werer (Ermias Shonga, 2006). Additionally, studies on the screening of different insecticides for Cotton bollworm control showed a declining efficacy of endosulfan at Werer Agricultural Research Center (WARC) (WARC, 1998) and commercial farms in Ethiopia (Geremew Terefe and Surachate, 2005). Application of different insecticides sequentially resulted in significant reductions in larval population as compared with repeated applications of the same insecticide (Salama et al., 2013). Helicoverpa armigera is a multi-resistant insect species; it can express more than one resistance mechanism to a particular insecticide group (Muhammad, 2007). Accordingly, designing an insecticide resistance management strategy for H. armigera is very crucial. The use of insecticide mixtures or mode of action rotation and sequential application is an important approach for managing insecticide resistance, which could delay or mitigate the onset of resistance development in arthropod pest populations (Cloyd, 2010). Pyrethroid insecticides are important in relation to other management options due to low tendency to accumulate in organism and short biodegradation period, and economic value led to overuse of pyrethriods with unavoidable consequences (Bhardwaj et al., 2020). Therefore, the present study was conducted to study the effectiveness of selected insecticide application sequences against H. armigera on cotton under field conditions. 2. Materials and Methods The experiment was conducted at Werer Agricultural Research Center (WARC), Amibara District, Gebresu zone of Afar National Regional State during the 2017 and 2018 cropping seasons under field conditions using irrigation. WARC is located at an altitude of 750 meter above sea level, at the latitude of 9o 20' 31"N, and longitude of 40o10' 11" E. The study areas is characterized by a mean annual rainfall of 540 mm which is erratic and mean maximum and minimum temperatures of 34.4 oC and 19.6 oC, respectively. The soil is vertisol with porosity and bulk density (0– 25cm depth) of 49.06% and 1.35 g cm–2, respectively (Wendmagen Chekole and Abere Mnalku, 2012). 2.1. Description of the Materials used for the research 2.1.1. Planting material The popular cotton variety used for the study was Deltpine-90, which was obtained from Werer Agricultural Research Center (WARC). 2.1.1. Insecticides Eight different insecticides were used for the experiment. These insecticides are recommended for the control of Cotton bollworm on cotton by WARC (Table 1). Table 1. Description of insecticides used in the experiment. Common name Trade name Chemical group Rate/ha Chlororfenapyr Tutan 36 SC Pyrole 225 ml Chlorantraniliprole Coragen 200 SC Diamide 125 ml Deltamethrin Decis 2.5 EC Pyrethroid 600 ml Lambda-cyhalothrin Karate 5 % EC Pyrethroid 400 ml Alpha-cypermethrin Fastac 100 g/lt Pyrethroid 300 ml Chlorpyriphos Pyriban 48 % EC Organophosphate 2000 ml Profenofos Proof 720 g/lt Organophosphate 900 ml Lufenuron+Profenofos Curador 55 EC IGR+Organophosphate 650 ml Note: EC = Emulsifiable concentrate, SC = Soluble concentrate, IGR = Insect Growth Regulators. 2.2. Treatments and Experimental Design The eight insecticides were systematically arranged in to six treatments (including one untreated check) and three spraying sequences (Table 2). The experiment was laid out as a Randomized Complete Block Design (RCBD) with four replications per treatment. An individual total plot size was 63 m2. The distance between the row to row and plant to plant was 90 cm and 20 cm, respectively. Zemedkun et al. Sequential application of insecticides for cotton bollworm management 43 2.3. Experimental Procedures 2.3.1. Planting date and methods The land was prepared by a tractor operated machine. Planting was done on 26 May 2017 and 21st May 2018 by hand. The plots were irrigated eight times by giving a 10-day interval after first irrigation and then watering every at the interval of 15 days up to the time of 65% boll opening period. Plots were weeded twice by hoeing and hand-weeded two times. All other recommended agronomic practices were applied to the plots. On each plot inspecting H. armigera infestation was started three weeks after germination and continued until the cotton plants matured. Ten plants per plot were randomly taken and tagged for the assessment of H. armigera infestation by checking leaves, squares, flowers, and bolls. From the tagged plants data were recorded on H. armigera eggs and larvae, square, flower, and boll damage of H. armigera. On an experimental plot, a total of three rounds of spray were applied using a hand-operated knapsack sprayer based on natural infestation when the economic threshold level was 10 larvae per 100 plants (WARC, 2015). The evaluated insecticide sprays were prepared according to the company’s recommended doses in a water application volume of 200 liters/hectare. 2.3.2. Dates of spraying The first round spray application was made on July 6th, 2017, and June 28th, 2018 coinciding with the period of formation of the squares and flowers of the plant, and the subsequent two sprays were applied at a 15-day interval. The second round spray application coincided with the pick square and flower formation period and the third round application coincided with the boll formation and boll opening period of the cotton plant. Ten plants were tagged in each plot and young shoot leaves, squares, flowers, and bolls were examined for data collection. Cotton bollworm egg and larvae, damaged squares, flowers, and bolls; non-target and beneficial insects on pre and post- spray count of 3, 5, 7, and 10 days were recorded. Data were collected on the number of days after treatment. At crop maturity and just before cotton- picking, healthy bolls per plant were counted from the ten predetermined plants including on plants from the control plots. Finally, seed cotton was harvested and weighed. 2.2. Data Analysis All data were analyzed using PROC GLM (SAS Version 9.0, SAS Institute, 1999). PROC UNIVARIATE was used to test data for normality and homogeneity of variance based on the Shapiro- Wilk statistic. To satisfy the assumptions of ANOVA, the pre and post-spray count mean data were square root transformed (√x+0.5). When F- values were significant (P < 0.05), means were compared by Fisher's Least Significant Difference (LSD) test. Percent efficacy for each treatment was computed based on the modified Abbotte’s formula by Fleming and Retenkarna, (1985). % Efficacy = [1 − (Ta ∗ Cb) / (Tb ∗ Ca)] Where, Ta = Post-treatment population in treatment, Cb = Pre-treatment population in check, Tb = Pre- treatment population in treatment, Ca = Post- treatment population in check. Zemedkun et al. East African Journal of Sciences Volume 15 (1) 41-50 44 Table 2. Insecticide treatments for spray sequence in field experiments during the 2017 and 2018 cropping seasons at Werer Agricultural Research Centre, Middle Awash Valley, Ethiopia. Treatment name Sequence of treatment 1st spray 2nd spray 3rd spray T1 chlorantraniliprole 200 SC @ 150 ml/ha chlorfenapyr 36 SC @ 225 ml/ha profenofos 720 G/L @ 900 ml/ha T2 deltamethrin 2.5 EC @ 600 ml/ha lufenuron + Profenofos 55 EC @ 650 ml/ha chlorfenapyr 36 SC @ 225 ml/ha T3 chlorfenapyr 36 SC @ 225 ml/ha chlorantraniliprole 200 SC @ 150 ml/ha lufenuron+profenofos 55 EC @ 650 ml/ha T4 lufenuron+profenofos 55 EC @ 650 ml/ha chlorfenapyr 36 SC @ 225 ml/ha alphacypermethrin 100 G/L @ 300ml/ha T5 chlorpyriphos 48 % EC @ 2l/ha lufenuron+profenofos 55 EC@650 ml/ha lambda-cyhalothrin 5% EC @ 480ml/ha T6 lambda-cyhalothrin 5 % EC @ 480ml/ha lambda-cyhalothrin 5 % EC @ 480 ml/ha lambda-cyhalothrin 5% EC @ 480ml/ha T7 Unsprayed Unsprayed Unsprayed 3. Results The results of the first round spray revealed that, the post spray larval and damaged square counts were significantly (P < 0.05) different among the treatments both in 2017 and 2018 cropping seasons (Tables 3). In both cropping seasons, the highest larval count, square numbers, and numbers of damaged flowers were recorded from control treatment and the lowest were recorded from chlorfenapyr treated plots (Tables 3). The results of the second round spray in the 2017 and 2018 cropping seasons revealed that the post- spray mean larvae count, damaged squares, flowers, and bolls revealed significant (P < 0.05) variations among the different insecticides applied (Tables 4). In both cropping years, among the tested insecticides, the highest larval controlling efficacy was obtained from spraying chlorfenapyr, while the lowest was from spraying lambda-cyhalothrin (Tables 4). The third round spray showed a significant (P < 0.05) difference for the post-spray larvae counts and damaged boll counts among the treatments in the 2017 cropping season (Table 5). In the 2018 cropping season, the post spray larval count, damaged squares, and boll count per plant revealed significant (P < 0.05) differences among the treatments (Table 5). There was a significant difference (P < 0.05) in the number of boll per plant among the treatments in both cropping years (Table 6). The highest numbers of boll per plant and seed cotton yield were obtained from the treatment with the rotation of chlorantraniliprole, Chlorfenapyr, Profenofos. However, the lowest numbers of boll per plant and seed cotton yield were obtained from the control treatment in both seasons (Table 6). The rotation of chlorantraniliprole, chlorfenapyr resulted in cotton yield advantages of 0.72 and 0.75 ton/ha in the 2017 and 2018 seasons compared to the commonly and repeatedly used lambda-cyhalothrin (Table 6). mailto:2.5EC@600ml/ha mailto:2.5EC@600ml/ha Zemedkun et al. Sequential application of insecticides for cotton bollworm management 45 Table 3. Means of pre and post-spray larva counts, damage square and damage flower, and efficacy of different insecticide tested at the 1st round spray application in a field experiment, Werer, during the 2017 and 2018 cropping seasons. 2017 cropping season Treatment name No. of larvae count/plant No. of damage squares/plant No. of damage flowers/plant % Efficacy Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray T1:chlorantraniliprole 200 SC 0.15(0.81) 0.03(0.73)c 0.28(0.87) 0.06(0.75)c 0.03(0.72) 0.02(0.72) 79.89 T2:deltamethrin 2.5% EC 0.18(0.82) 0.13(0.79)ab 0.30(0.89) 0.14(0.80)b 0.08(0.75) 0.03(0.72) 31.04 T3:chlorfenapyr 36SC 0.20(0.83) 0.04(0.73)c 0.50(0.10) 0.04(0.74)c 0.08(0.76) 0.04(0.73) 81.90 T4:lufenuron+profenofos 55% EC 0.15(0.81) 0.04(0.74)c 0.28(0.88) 0.09(0.77)bc 0.03(0.72) 0.01(0.71) 71.84 T5:chlorpyriphos 48 % EC 0.20(0.84) 0.09(0.77)bc 0.30(0.89) 0.11(0.78)bc 0.08(0.75) 0.04(0.74) 54.74 T6:lambda-cyhalothrin 5 % EC 0.18(0.82) 0.08 (0.76)bc 0.28(0.87) 0.11(0.78)bc 0.10(0.77) 0.04(0.73) 55.17 T7:Unsprayed 0.18(0.82) 0.18(0.82)a 0.15(0.81) 0.34(0.92)a 0.03(0.72) 0.06(0.74) - LSD ( 0.05) Ns 0.050 Ns 0.051 Ns Ns CV (%) 8.15 4.44 12.47 4.34 10.43 4.96 2018 cropping season Treatment Name No. of larvae counts/plant No. of damage squares/plant No. of damage flowers/plant % Efficacy Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post -spray T1:chlorantraniliprole 200 SC 0.58(1.03) 0.06(0.77)c 0.85(1.12) 0.02(0.72)c 0.0(0.71) 0.03(0.73) 80.43 T2:deltamethrin 2.5% EC 0.33(0.90) 0.12(0.78)b 0.38(0.92) 0.68(1.07)ba 0.0(0.71) 0.08(0.76) 26.92 T3:chlorfenapyr 36SC 0.75(1.09) 0.09(0.77)b 0.95(1.18) 0.18(0.82)bc 0.05(0.74) 0.08(0.76) 75.00 T4:lufenuron+profenofos 55% EC 0.33(0.91) 0.04(0.73)b 0.30(0.89) 0.03(0.72)c 0.0(0.71) 0.02(0.72) 76.92 T5:chlorpyriphos 48 % EC 0.50(0.99) 0.02(0.81)b 0.50(0.96) 0.48(0.98)bac 0.05(0.74) 0.04(0.73) 40.00 T6:lambda-cyhalothrin 5 % EC 0.30(0.89) 0.09(0.77) b 0.18(0.81) 0.30(0.89) cb 0.0(0.71) 0.01(0.71) 41.67 T7:Unsprayed 0.58(1.03) 0.29(0.88)a 0.78(1.08) 1.16(1.23)a 0.0(0.71) 0.09(0.77) - LSD ( 0.05) Ns 0.07 Ns 0.29 Ns Ns CV (%) 11.9 6.34 20.5 21.7 2.9 4.1 Note: Means followed by the same letter(s) within a column are not significantly different from each other at a 5% level of significance. Values in parentheses pre- and post-spray mean data were square-root- transformed. % Efficacy = Percent efficacy. Zemedkun et al. East African Journal of Sciences Volume 15 (1) 41-50 46 Table 4. Means of pre and post-spray counts of larvae counts, damage square, flower, bolls, and efficacy of different insecticides tested at the 2nd round rotation spray application, Werer, during the 2017 and 2018 cropping seasons. 2017 cropping season Treatment Name No. of larvae count/ plant No. of damage square/ plant % efficacy No. damage flowers/ plant No. damage bolls/plant Pre-spray Post-spray mean Pre-spray Post-spray mean Pre-spray Post-spray mean Pre-spray Post-spray mean T1:Chlorfenapyr 36 SC 0.40(0.95) 0.07(0.75)d 0.55(1.02) 0.13(0.79)d 85.61 0.23(0.85) 0.07(0.75) 0.08(0.76) 0.06(0.75) T2:Lufenuron+profeno 55 EC 0.45(0.97) 0.15(0.81)bcd 0.73(1.11) 0.31(0.90)bcd 68.82 0.20(0.83) 0.12(0.79) 0.15(0.81) 0.12(0.79) T3:Chlorantraniliprole 200 SC 0.38(0.93) 0.09(0.77)cd 0.50(0.99) 0.16(0.81)cd 76.61 0.15(0.80) 0.13(0.79) 0.18(0.82) 0.13(0.79) T4:Chlorfenapyr 36 SC 0.40(0.95) 0.11(0.78)cd 0.95(1.16) 0.38(0.93)bcd 75.15 0.33(0.91) 0.14(0.80) 0.18(0.82) 0.11(0.78) T5:Lufenuron+profeno 55 EC 0.50(0.10) 0.18(0.83)bc 1.23(1.30) 0.43(0.96)bc 66.09 0.23(0.85) 0.17(0.81) 0.23(0.84) 0.15(0.81) T6:Lambdacyhalothrin 5%EC 0.48(0.99) 0.23(0.85)b 1.18(1.28) 0.58(1.03)b 55.69 0.33(0.91) 0.13(0.79) 0.28(0.88) 0.18(0.82) T7:Unsprayed 0.55(1.02) 0.78(1.13)a 0.98(1.21) 1.13(1.27)a - 0.25(0.86) 0.24(0.86) 0.05(0.74) 0.19(0.83) LSD ( 0.05) Ns 0.06 Ns 0.15 Ns Ns Ns Ns CV (%) 8.32 4.96 16.74 10.68 9.83 8.12 9.51 5.14 2018 cropping season Treatment Name No. of larvae count/plant No. of damage square/plant % efficacy No. damage flowers/plant No. damage bolls/plant Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray T1:Chlorfenapyr 36 SC 0.23(0.84) 0.05(0.74)b 0.28(0.88) 0.13(0.794)c 80.85 0.0(0.71) 0.03(0.73)c 0.03(0.72) 0.06(0.75)c T2:Lufenuron+profeno 55 EC 0.55(1.61) 0.213(0.84)ba 0.98(1.19) 0.49(0.99)ba 66.71 0.10(0.77) 0.13(0.79)ba 0.30(0.89) 0.19(0.83)ba T3:Chlorantraniliprole200SC 0.33(0.91) 0.113(0.78)b 0.60(1.03) 0.36(0.92)bac 70.18 0.15(0.80) 0.06(0.75)bc 0.23(0.85) 0.15(0.81)bac T4:Chlorfenapyr 36 SC 0.20(0.84) 0.063(0.75)b 0.33(0.89) 0.27(0.87)bc 73.08 0.03(0.72) 0.07(0.75)bc 0.13(0.79) 0.09(0.77)bc T5:Lufenuron+profeno 55 EC 0.50(0.99) 0.213(0.84)ba 0.83(1.13) 0.34(0.92)bac 63.38 0.03(0.72) 0.10(0.77)ba 0.30(0.89) 0.23(0.85)a T6:Lambdacyhalothrin5%EC 0.43(0.96) 0.231(0.85)ba 0.73(1.10) 0.53(1.00)ba 53.12 0.10(0.77) 0.07(0.75)bc 0.28(0.88) 0.21(0.84)a T7:Unsprayed 0.35(0.92) 0.406(0.95)a 0.50(0.99) 0.56(1.02)a - 0.08(0.76) 0.16(0.81)a 0.20(0.84) 0.23(0.85)a LSD ( 0.05) Ns 0.12 Ns 0.14 Ns 0.05 Ns 0.06 CV (%) 9.22 9.50 15.41 10.14 8.64 3.94 7.47 5.29 Note: Means followed by the same letter(s) within a column are not significantly different from each other at a 5% level of significance. % Efficacy = Percent efficacy. Values in parentheses of pre and post spray means data were square-root-transformed. Zemedkun et al. Sequential application of insecticides for cotton bollworm management 47 Table 5. Means of pre and post-spray larva counts, damage square, flower, bolls, and efficacy of different insecticides tested at the 3rd round rotation spray application, Werer, 2017 and 2018 cropping seasons. 2017 cropping season Treatment Name No. of larvae count/plant No. damage squares/plant % Efficacy No. damage flowers/plant No. damage bolls/plant Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray T1:Profenofos 72%EC 0.15(0.80) 0.03(0.73)b 0.28(0.87) 0.04(0.74) 79.89 0.13(0.79) 0.03(0.72) 0.18(0.82) 0.11(0.78)b T2:Chlorfenapyr 36SC 0.25(0.86) 0.04(0.74)b 0.38(0.93) 0.03(0.73) 83.10 0.15(0.80) 0.03(0.73) 0.15(0.81) 0.09(0.77)b T3:Lufenuron+profenofos 0.30(0.89) 0.08(0.76)b 0.33(0.90) 0.05(0.74) 76.86 0.15(0.81) 0.03(0.73) 0.25(0.86) 0.10(0.77)b T4:Alphacypermethrin 100%EC 0.20(0.84) 0.04(0.73)b 0.25(0.86) 0.08(0.76) 81.90 0.10(0.77) 0.02(0.72) 0.28(0.87) 0.12(0.79)b T5:Lambda-cyhalothrin 5%EC 0.18(0.82) 0.07(0.75)b 0.25(0.87) 0.07(0.75) 62.07 0.08(0.75) 0.03(0.72) 0.13(0.79) 0.10(0.77)b T6:Lambda-cyhalothrin 5%EC 0.23(0.85) 0.10(0.77)b 0.30(0.894) 0.11(0.78) 57.09 0.28(0.88) 0.05(0.74) 0.23(0.85) 0.21(0.84)a T7:Unsprayed 0.18(0.82) 0.18(0.86)a 0.25(0.86) 0.26(0.86) - 0.25(0.86) 0.09(0.77) 0.25(0.86) 0.24(0.86)a LSD ( 0.05) Ns 0.06 Ns Ns Ns Ns Ns 0.048 CV (%) 7.98 5.28 8.71 8.98 8.71 4.11 12.18 4.00 2018 cropping season Treatment Name No. of larvae count/plant No. damage squares/plant % Efficacy No. damage flowers/plant No. damage bolls/plant Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray Pre-spray Post-spray T1:Profenofos 72%EC 0.30(0.89) 0.06(0.75)b 0.38(0.93) 0.03(0.72)b 84.27 0.10(0.77) 0.03(0.72) 0.20(0.84) 0.07(0.75)b T2:Chlorfenapyr 36SC 0.33(0.91) 0.07(0.75)b 0.38(0.92) 0.04(0.74)b 82.26 0.15(0.80) 0.03(0.73) 0.18(0.82) 0.13(0.79)b T3:Lufenuron+profenofos 0.28(0.88) 0.07(0.75)b 0.26(0.87) 0.08(0.76)b 79.03 0.15(0.80) 0.02(0.73) 0.28(0.88) 0.14(0.79)b T4:Alphacypermethrin100%EC 0.33(0.91) 0.09(0.77)b 0.33(0.89) 0.08(0.76)b 75.82 0.08(0.76) 0.03(0.72) 0.25(0.87) 0.21(0.84)b T5:Lambda-cyhalothrin 5%EC 0.30(0.89) 0.14(0.79)b 0.50(0.99) 0.13(0.79)b 61.56 0.08 (0.76) 0.04(0.74) 0.10(0.77) 0.16(0.81)b T6:Lambda-cyhalothrin 5%EC 0.33(0.90) 0.16(0.81)b 0.38(0.93) 0.16(0.81)b 59.68 0.15(0.81) 0.03(0.72) 0.25(0.86) 0.19(0.82)b T7:Unsprayed 0.33(0.91) 0.39(0.93)a 0.30(0.89) 0.36(0.92)a - 0.08(0.76) 0.11(0.78) 0.25(0.87) 0.43(0.96)a LSD ( 0.05) Ns 0.06 Ns Ns Ns Ns Ns 0.05 CV (%) 7.98 5.28 8.71 8.98 8.71 4.11 12.18 4.00 Note: Means followed by the same letter(s) within a column are not significantly different from each other at 5% level of significance. % Efficacy = Percent efficacy. Values in parentheses of pre and post spray mean data were square-root-transformed. Zemedkun et al. East African Journal of Sciences Volume 15 (1) 41-50 48 Table 6. Means of bolls number per plant and seed cotton yield in a field experiment, Werer, during the 2017 and 2018 cropping seasons. Treatment no. Spray sequence of treatment 2017 cropping season 2018 cropping season Healthy boll/plant Seed cotton yield (t ha-1) Healthy boll/plant Seed cotton yield (t ha-1) 1st spray 2nd spray 3rd spray 1 chlorantraniliprole 200 SC @150ml/ha chlorfenapyr 36 SC @225ml/ha profenofos 720 G/L @900ml/ha 16.53a 3.84a 20.85a 3.17a 2 deltamethrin 2.5EC @600ml/ha lufenuron + Profenofos 55EC @650ml/ha chlorfenapyr 36 SC @225ml/ha 12.85b 3.35bc 12.68b 2.48b 3 chlorfenapyr 36 SC @225ml/ha chlorantraniliprole 200 SC @150ml/ha lufenuron+profenofos 55EC @ 650ml/ha 14.08b 3.68ab 15.53ab 3.08a 4 lufenuron+profenofos 55EC @650ml/ha chlorfenapyr 36 SC @225ml/ha alphacypermethrin 100G/L @300ml/ha 14.15b 3.51abc 14.05b 2.42b 5 chlorpyriphos 48% EC @2l/ha lufenuron+profenofos 55EC @650ml/ha lambda-cyhalothrin 5% EC @480ml/ha 12.63b 3.39bc 10.5b 2.31bc 6 lambda-cyhalothrin 5% EC @480ml/ha lambda-cyhalothrin 5% EC @480ml/ha lambda-cyhalothrin 5% EC @480ml/ha 12.40bc 3.12c 10.13b 2.26bc 7 Unsprayed Unsprayed Unsprayed 10.38c 2.56d 9.0b 1.91c LSD ( 0.05) 2.05 0.44 6.78 5.08 CV (%) 10.39 8.87 15.37 13.57 SE 0.69 0.15 2.28 0.15 Note: Means followed by the same letter (s) within a column are not significantly different from each other at 5% level of significance. mailto:2.5EC@600ml/ha mailto:2.5EC@600ml/ha Zemedkun et al. Sequential application of insecticides for cotton bollworm management 49 4. Discussion The present study indicated application of chlorantraniliprole 200SC and chlorfenapyr 36 SC resulted in a better control of H. armigera larva on cotton. The results is consistent with the findings of Cordova et al. (2006) and Bheemanna et al. (2008) who found that chlorantraniliprole 20 SC @40 g a.i. ha-1 effectively controlled H. armigera on cotton by causing impaired regulation, paralysis, and ultimately death of sensitive species. Similarly, Aslam et al. (2004) and Perini et al. (2016) also reported that due to knockdown chemical nature, chlorfenapyr effectively controlled H. armigera. For the long time, year to year and repeated application within a season of lambda-cyhalothrin and deltamethrin had resulted effective for controlling of H. armigera in cotton. That lufenuron insect growh regulator insecticide also resulted in an effective control of the pest by forming abnormal new cuticle and death of the insect was earlier reported by Gopal and Tarikui (2014) and Tarikul et al. (2015). Confirming the results of this study, Vittozzi et al. (2001) reported that Profenophos insecticide toxicity can occur in two ways: inhibition of acetylcholine esterase, and cytotoxic effects on immune cells. Sequential application of chlorantraniliprole, chlorfenapyr, profenofos insecticides resulted in the lowest H. armigera larvae population due to high controlling efficacy. However, the lowest controlling efficacy was from conventional insecticides lambda- cyhalothrin applied in three sequences. The results this study revealed that sequential application of a mixture of insect growth regulator and organophosphate insecticides provided a good control of the H. armigera larva pest. The results confirmed that in both cropping seasons during the experiment, inclusion of deltamethrin in the rotation reduced the insecticide efficacy in controlling cotton bollworm. The results of this study agrees with the findings of Salama et al. (2013) who reported that the sequential application of conventional insecticides in rotation with biocides, IGRs, and anti-molting compounds provided a good average reduction in the larval population of cotton bollworms. Similarly, Rabia et al. (2016) suggested a rotational scheme of application of insecticides with different modes of action to reduce the onset of development insecticide resistance in H. armigera. Many studies have evaluated the effects of insecticide mixtures in suppressing populations and damage of H. armigera insect pests (Martin et al., 2003; Hamed et al., 2006; Nayak and Daglish, 2007; Borude et al., 2018). Pesticide mixture has been recommended for use as a resistance management strategy based on the assumption that insects will not develop resistance to multiple modes of action simultaneously (Warnock and Cloyd, 2005). 5. Conclusion The results of this study have revealed that application of deltamethrin and lambda-cyhalothrine reduced their efficacy for controlling Helicoverpa armigera; thus, there is a need to replace them with the new insecticides chlorfenapyr for providing good control against H. armigera on cotton. Application of insecticide with a different mode of action in rotations resulted in a significantly higher cotton yield than the convectional way of spraying lambda-cyhalothrin repeatedly. Future studies are needed to monitor the level of insecticide resistance and design insecticide resistance management strategies. 6. 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