POPULATION DYNAMICS AND MANAGEMENT OF PEST COMPLEX OF OKRA, Abelmoschus esculentus (L.) MOENCH
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Date
2003
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AAU, Anand
Abstract
Investigations were carried out on population dynamics, varietal susceptibility, evaluation of IPM modules and never insecticides for management of pest complex of okra at B. A. College of Agriculture, Gujarat Agricultural University, Anand Campus, Anand during the year 2000-01 and 2001-02. Studies on population dynamics of jassid, Amrasca biguttula biguttula (Ishida) on okxa revealed that the pest appeared after 3rd week of sowing and remained active throughout the kharif season. The population reached to its peak during 9th, 6th and 12th week after sowing (WAS) in May, June and July plantings, respectively. It was also observed that May and July plantings supported higher population as compared to June sown crop. Correlation studies between the population and weather factors (WF) indicated significant negative relationship between bright sun shine hours (BSS), maximum temperature (Max T), Mean temperature (MT), relative humidity (RH), temperature range (TR) and population for May sown crop. However, all the factor except RH1 and Min T showed significant positive correlation on the population in July planting, which suggesting that July planted crop proved more vulnerable to the attack and build up of this pest. Thus, the study clearly revealed that jassid population increased with decrease in BSS and evening relative humidity (RH2) between the range of 5 to 2.1 hrs and 72.15 to 80.40 per cent, respectively. Infestation of aphid, Aphis gossypii Glover appeared on okra crop during 5th\ 3rd and 3rd WAS in May, June and July plantings, respectively. It has been also found that the aphid activity was high in June sown crop, compared to May and July plantings. Among the different physical factors of environment, BSS, MT, Max T, TR, mean vapour pressure deficit (MVPD) and evening pressure deficit (VPD2) showed significant negative correlation, whereas RH2, MRH and rain fall (RF) had positive correlation with the build up of aphid population. The regression study indicated that BSS and Max T in the range of 1.20 to 5.00 hrs and 30 to 32 °C were found favourable for the build up of the pest population. The study further revealed that damage to shoots due to Earias vittella (Fab.) started after 3rd WAS in June planted crop and 4th WAS on crops sown in May and July. The pest started damaging the fruits, when the crop was at fruiting stage. The damage commenced 7th , 8th and 8th week after sowing in three respective dates of plantings. Thus, it is evident from the study that the pest appeared earlier in May and June planted crops compare to July planting. Correlation studies indicated that RH1, VP1, VP2 and MVP had significant positive effect, whereas VPD caused significant negative effect on the pest activity and damage, whereas none of the weather parameters had significant influence on shoot infestation in the May and June planted crops. It was also observed that BSS, Max T, Min T, MVP, VPD1, MVPD and RF have significant negative correlation in May sown crop. Similar correlation was also observed for RH1, RH2, MRH, VPl, MVP and WS, when the crop planted in July. Regression study indicated that BSS and Max T played an important role for fruit damage in May sown crop. Considering the incidence of different pest and role of weather factors for fluctuation of their populations in three dates of sowing, the early planted crop (15th May) showed fast and luxuriant growth resulted in tolerance to these pests, whereas late sown crop (15th July) showed slow growth and become more favourable to the attack of the pests under study. Looking to the yield and incidence of different pests, May planting is more suitable for obtaining higher marketable fruit yield, and minimize damage of E. vittella to fruits. The studies on population dynamics of jassid in summer season revealed that the pest appeared 3rd and 4th WAS, when the crop planted in February and March. The population attained its peak during 10th (18.30 jassid per leaf) and 11th (16.68 jassid per leaf) WAS in February and March sown crops, respectively. The correlation study for the effect of weather factors indicated positive correlation between jassid and BSS, Min T, Max T, MT, VPD1, VPD2 and MVPD, when the crop was planted in February, whereas such effect of MT, RHl, RH2, MRH, VPD1, VPD2 and MVPD was observed in March planting with highly significant negative correlation with TR. Further, it has been observed that none of the weather factors showed significant effect on the population, when the crop was planted in April. Regression study indicated that Min T (20.75 to 24.75 °C) and MVP (20.85 to 22.60 mm of Hg) helped in suppressing the pest population. The results on population of aphids revealed that aphid (A. gossypii) appeared 3rd, 4th and 4th WAS in February, March and April sown crops. But the pest population remained very low during the summer season. The highest population of whitefly, Bemisia tabaci (Gennadius) was recorded 5th, 7th and 4th WAS with 1.11, 0.98 and 0.81 whitefly per leaf on February, March and April sown crops, respectively. It was also observed that pest was active throughout the crop season in march sown crop. Correlation study indicate that among different physical factors, BSS showed significant negative association with the population in February sown crop, whereas BSS, Max T, MT, VPD2, MVPD and TR indicated significant positive correlation and RH2 and MRH showed significant negative correlation in April sown crop. Regression study showed that the population was at increasing tremendous when ranged BSS from 8.85 to 10.90 hrs.
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AGRICULTURAL ENTOMOLOGY, AGRICULTURE, MANAGEMENT