Browsing by Author "Lekha, M"

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    Management of pests of grain cowpea, (Vigna unguiculata (L.) Walp.) using cashew nut shell liquid based botanical pesticide
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 2022-11-04) Aiswarya Mohan.; Lekha, M
    The study entitled “Management of pests of grain cowpea, (Vigna unguiculata (L.) Walp.) using cashew nut shell liquid based botanical pesticide” was conducted at Department of Agricultural Entomology, College of Agriculture, Vellayani and Krishi Vigyan Kendra, Sadanandapuram, Kerala Agricultural University during 2019-2022 to evaluate the efficacy of cashew nut shell liquid (CNSL) for the management of pests of grain cowpea. Laboratory evaluation of CNSL against pests and natural enemies of grain cowpea was conducted using the treatments viz., CNSL 20% EC at 0.3, 0.5 and 1%, CNSL 20% EC at 0.3 % followed by the application of Beauveria bassiana 2%, B. bassiana 2% alone, chemical check, dimethoate 30 EC 0.05% and untreated control. The test insects viz., pod bug, Riptortus pedestris Fabricius (both nymphs and adults) and syrphid fly larvae (Paragus sp.) were used in the study. The trial was conducted with topical application of CNSL on test insects and fed with treated and untreated food. In both the methods, CNSL 20 % EC at 1% recorded significantly higher percentage mortality throughout the observation period attaining cent per cent mortality at 96 hours after treatment (HAT). In topical application of CNSL with untreated food, the percentage mortality was comparatively low during the initial hours of treatment in lower concentrations of CNSL viz., 0.3% (no mortality observed till 96 HAT) and 0.5% (0.00, 20.00, 40.00 and 40.00 respectively at 24, 48, 72 and 96 HAT) than the topical application method with treated food. The corresponding mortality at 0.3 and 0.5% of CNSL 20% EC was 0.00, 20.00, 40.00 and 100.00 per cent respectively at 24, 48, 72 and 96 HAT. In the case of R. pedestris adults, the higher concentrations of CNSL 20 % EC at 0.5 and 1% attained cent per cent mortality at 4 days after treatment (DAT). No significant difference was observed in the percentage mortality of R. pedestris adults among different concentrations of CNSL (0.3, 0.5 and 1%) up to 3 DAT. Laboratory evaluation of different treatments on syrphid fly larvae indicated the safety of CNSL based treatments. During the field evaluation, higher concentrations of CNSL 20 % EC at 0.5 and 1% significantly reduced the population of aphids, Aphis craccivora Koch and pod bugs, R. pedestris as compared to other botanicals and untreated control during the vegetative stage of the crop. A gradual reduction in the mean population of aphids was observed in CNSL 20 % EC at 0.5 and 1% from 1 DAT to 7 DAT, but a hike in the population was observed at 14 DAT. The values being 133.33, 93.33, 73.33 and 50.00 plant-1 in the case of CNSL 20 % EC 0.5 % and 53.33, 43.33, 35.00 and 18.33 plant-1 with CNSL 20 % EC 1% respectively at 1, 3, 5 and 7 DAT and the mean population reached 96.67 and 66.67 plant-1 respectively at 14 DAT. More than 85 per cent reduction over untreated control was noticed in CNSL 20 % EC 1% among the botanicals at all intervals after spraying. No adverse effect of treatments was observed on the natural enemy population in the field. During the reproductive stage, all the CNSL containing treatments recorded more than 80 % population reduction over untreated control from 1 DAT to 7 DAT and the observation on the mean population of aphids indicated the efficacy of CNSL 20 % EC at 1% with a significantly lower population of aphids(43.33 plant-1) at 14 DAT. Regarding pod bugs, the mean population at the pod formation stage was significantly low in the plants treated with CNSL 20 % EC at 0.5 and 1% in all the observations and the values being 5.33 and 4.00 plant-1, 2.67 and 2.00 plant-1, 1.00 and 0.33 plant-1 and 0.33 and 0.00 plant-1 at 1, 3, 5 and 7 DAT respectively. But at 14 DAT, though all the treatments showed a slight increase in the population, CNSL containing treatments recorded significantly lower population comparable to that of chemical check, dimethoate 30 EC 0.05% and resulted in a percentage reduction of more than 80.00 from 3 DAT onwards. Application of CNSL 20 % EC at 1 and 0.5 % attained a higher yield of 29.17 and 26.77 g plant-1 and was on par with the chemical check, dimethoate 30 EC 0.05% (30.00 g plant-1). A laboratory trial was carried out to study the effect of CNSL on the storage pest, Callosobruchus chinensis L. using cowpea seeds. Crushed cashew nut shell at 40 g/kg seed showed very good repellency of C. chinensis and was seemed to be on par with chemical check. At 24 HAT, cent percentage mortality of C. chinensis was recorded in crude CNSL at 6 mL kg-1 seed and was significantly superior to chemical check. Crude CNSL (2, 4 and 6 mL kg-1) as well as CNSL 20 % EC formulation (4 and 6 mL kg-1 seed) recorded significantly higher mortality of C. chinensis when released to treated seeds at 48, 72 and 96 HAT. Oviposition, progeny emergence and grain damage was not observed in any of the treatments except in seeds treated with crushed cashew nut shell at 20 g kg-1 seed with 46.67 eggs, 30.67 adults and 38.33 grains damaged. None of the treatments adversely affected the germination of seeds, since cent percentage germination was noticed in all the treatments except in chemical check (92.00 per cent) by 7 DAT. However, the germination parameters viz., seedling length, seed vigour index and speed of germination differed slightly among the treatments. The efficacy of CNSL 20 % EC at 0.5 and 1% against A. craccivora and R. pedestris were proved. Since crude CNSL and CNSL EC formulation were found equally effective in managing C. chinensis when used as seed treatment, considering the germination parameters, crude CNSL at 2 and 4 mL kg-1 seed as well as CNSL 20 % EC at 4 and 6 mL kg-1 seed were found promising for seed treatment against bruchids.
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    Management of the leaf roller complex on rice Oryza sativa L
    (Division of Agricultural Entomology, College of Agriculture, Vellayani, 2003) Lekha, M; Premila, K S
    The magnitude and intensity of leaf roller complex and natural enemies at different growth stages of the rice crop were assessed in a survey conducted during Mundakan season of 2002, adopting random sampling technique in Kalliyoor panchayat of Thiruvananthapuram district. The survey revealed the occurrence of two different species of leaf roller viz., Cnaphalocrocis medinalis (Guenee) and Marasmia patnafis (Bradley). The distribution pattern of these two species in the n ce ecosystem varied. C. medinalis had a population peak during the vegetative stage and showed a gradual decline as the crop growth progressed, whereas, M. patnalis had a population peak during the early reproductive stage compared to vegetative and late reproductive stage. The natural enemies recorded from the rice ecosystem incl ude three parasites and ten predators. The distribution of natural enemies in the rice ecosystem revealed that the population of parasites and predators showed a gradual increase from vegetative to reproductive phase. From the field experiment, it was evident that the synthetic insecticides alone and botanicals + half dose synthetic insecticides were efficient in suppressing the pbpulation of rice leaf roller. The treatments with botanicals alone did not show any significant reduction in the population of leaf roller compared to control. G. tr iangulifer, a specific larval parasite of rice leaf roller, was unaffected by the botanicals, synthetic insecticides and their combinations at 30 OAT. In the case of X flavolineata and Cot esia sp., only an initial suppression was noticed in insecticide included treatments. Later it was found to be safe. All these treatments were found to be relatively safe to predatory beetles. But Agriocnemis sp., spiders, predatory bugs and Conocephalus sp. was adversely affected by the insecticide included treatments. Botanicals were safe to all the natural enemies observed but they were ineffective against rice leaf roller. The yield obtained was also the highest in synthetic insecticides alone and botanicals + half dose of synthetic insecticide treatments and were on par. Overall assessment of the results obtained revealed that synthetic insecticides alone and botanicals + half dose of synthetic insecticides were equally effective in controlling rice leaf roller and safe to its specific parasites and predators. For other natural enemies, it showed a varying trend. In some cases there was an initial suppression and then recolonization occurred. From this result, it was clear that botanicals + half dose synthetic insecticides were as equally effective as full dose of synthetic insecticides in suppressing the pest and in protecting natural enemies. Hence we can substitute the full dose of synthetic insecticides with combination of botanicals (either NSO three per cent or azadirachtin 0.004 per cent) and half dose of synthetic insecticides (either quinalphos 0.0025 per cent or imidacloprid 0.0025 per cent) for an ecofriendly management of rice leaf roller.