PG Thesis

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    Biocontrol of pests of vegetable cowpea (Vigna unguiculata sub sp. sesquipedalis (L.) verdcourt)
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 1997) Bindu , S S; Sudharma, K
    Monitoring of the incidence of pests and their natural enemies was carried out in the heavily insecticide sprayed vegetable cowpea plots in farmers' fields in two locations viz. Kalliyoor and Palappur in Thiruvananthapuram District and in the unsprayed crop raised in the Instructional Farm, College of Agriculture, Vellayani, during kharif and rabi, 1996. The results of the monitoring revealed that the pea aphid, A. craccivora , the pod bugs R. pedestris and C. gibbosa and the pod borers H. armigera, L. boeticus and M. testulalis were the major pests that attacked vegetable cowpea both in the insecticide sprayed as well as in the unsprayed plots. The pea aphid was persistent in the insecticide sprayed fields where as in the unsprayed fields, they were not seen upto 35 days after sowing, in both kharif and rabi season. The pod bugs and pod borers were seen throughout the cropping period with increase in the post flowering period in both sprayed and unsprayed crop. Attack of the american serpentine leaf miner L. trifolii was observed only in the insecticide sprayed fields and was present in rabi as well as in the kharif seasons The parasitoids that were encountered were A. nigrotibiali$, Charops sp., Salius sp. and T. subvirescens and the predators were M. sexmaculatus, M. crocea, Scyanus sp., E. stali, S. geminate and X. scutellarae. The population of the natural enemies was higher during the rabi season than that during kharif season. The population of the pests and natural enemies in the insecticide sprayed and unsprayed plots were compared using students ‘t' test and the results revealed that the pest were more in the un sprayed plots but the population was higher only for a shorter period and it was effectively checked by the natural enemies, the population of which synchronized with that of the pests. There was significantly higher population of natural enemies in the unsprayed plots when compared to unsprayed plots. The role of the green lacewing C. carnea in the management of the vegetable cowpea pests was studied through replicated field trials conducted at College of Agriculture, Vellayani during 1996. The impact of biorationals viz., neem oil and tobacco decoction and insecticide, malathion on the predator C. carnea and in their effectiveness in management of cowpea pests was also studied in the field experiment. C. carnea released @ 50 per plot at fortnightly intervals effectively checked the aphid population. Among the botanicals, tobacco decoction 2 per cent was found to be effective in controlling the aphids, pod bugs and pod borers. Neem oil emulsion 10 per cent when applied at fortnightly intervals was also found to be significantly superior to the untreated control. However the infestation by aphids and the pod bugs was' less in all the treatments when compared to control. Though the control plot did not show significant reduction in yield, the quality of the produce was reduced due to the pest infestation. C. carnea @ 100 per plot at fortnightly and monthly intervals were effective against pod bugs. The pod borers were effectively checked by C. carnea • 50 arid 100 per plot. In general the monthly release of C. carnea was comparatively less effective in controlling the pests. The botanicals did not show any deleterious effect on C. carnea. When the yield was assessed in terms of weight and number of pods harvested, significantly higher yield was recorded only in plots treated with tobacco decoction 2 per cent when compared to untreated control.
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    Mitigating production vulnerability of banana through weather based crop insurance: An economic analysis
    (Department of Agricultural Economics, College of Agriculture, Vellayani, 2019) Ajmal, S; Paul Lazarus
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    Effect of herbicides and chemical characteristics of soil on microbial biomass carbon and enzyme activity
    (Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 2017) Amritha, K; Durga Devi, K M
    Weed competition is one of the major factors limiting rice production in the tropics. Due to the scarcity and high cost of labour, weed management with herbicides is widely practiced. The problem associated with herbicides is the persistence of their residues in soil which interact with microorganisms thereby altering the microbial diversity and soil enzyme activity. Hence, the present investigation entitled “Effect of herbicides and chemical characteristics of soil on microbial biomass carbon and enzyme activity” was undertaken at College of Horticulture, Vellanikkara during 2016-2017. The objectives were: (i) to determine the impact of pre and post emergence herbicides on microbial biomass carbon and the soil enzymes namely dehydrogenase, urease, and phosphatase and (ii) to study the influence of chemical characteristics of the soil on microbial biomass carbon and enzyme activity. Representative soil samples were collected during March-April, 2016 from four sites viz., rice field of Agricultural Research Station, Mannuthy (medium organic matter soil with a history of herbicide application: S1 Control), non- cropped area of Agricultural Research Station, Mannuthy (medium organic matter soil without a history of herbicide application: S1 Absolute control), rice field of Kole land, Alappad (high organic matter soil with a history of herbicide application: S2 Control), and non- cropped area of Kole land, Alappad (high organic matter soil without history of herbicide application: S2 Absolute control). Physical, chemical, and biological characterization of the soil samples were done before starting the experiment. Pot culture experiment with rice variety Jyothi was conducted in the kharif season of 2016 with twelve treatments and six replications in factorial CRD (four herbicides under each soil type + four controls). The herbicides included pendimethalin, oxyfluorfen, bispyribac-sodium, and cyhalofop-butyl. Pre emergence herbicides (pendimethalin and oxyfluorfen) were applied at six days after sowing (DAS) and post emergence herbicides (bispyribac-sodium and cyhalofop-butyl) at 16 DAS. Soil samples were analysed at six intervals viz., on the day of herbicide application, but two hour before, then at 7, 15, 30, and 60 days after herbicide application (DAHA) and at harvest so as to evaluate the changes in the chemical and biological properties. Data on analysis of soil samples before the period of experimentation revealed that soils from rice field of Kole land recorded physical, chemical, and biological characteristics which are more favourable for the growth of microflora. The chemical characteristics like pH, electrical conductivity, and organic carbon followed a decreasing trend towards the harvest in all the treatments. Decline in microbial biomass carbon (MBC) was observed upto harvest except on 60 DAHA. Pendimethalin treatment in S1 soil (medium organic matter) registered the highest per cent reduction in MBC with respect to control at different intervals. Percentage reduction in MBC due to herbicide application was comparatively lower in S2 (high organic matter) throughout the period of study. Activity of dehydrogenase, urease, acid phosphatase and alkaline phosphatase was higher in S2 compared to S1. In all cases, the enzyme activity increased upto 60 DAHA with slight variations and declined thereafter registering a peak at 60 DAHA. Among the four enzymes studied, urease recorded maximum increase at 60 DAHA followed by acid phosphatase, dehydrogenase and alkaline phosphatase. All the vegetative and yield parameters of rice were high in S2 (high organic matter soil) irrespective of the treatment combinations. Adverse effects of herbicides on the plant characters were minimal. Whole plant analysis for major nutrients also exhibited appreciably higher values in S2 compared to S1. Out of the five biological parameters analysed, microbial biomass carbon showed the highest variation from control at all the sampling intervals. The adverse effects of herbicides on MBC and enzyme activity followed the order: pendimethalin > bispyribac-sodium > oxyfluorfen > cyhalofop-butyl. Organic carbon had highly significant and positive correlation with all the biotic components viz., MBC, dehydrogenase, urease, acid and alkaline phosphatase activity at different sampling intervals consequent to herbicide application. Further study should be focused on identification of microbial diversity, effect of rhizosphere on biological activity and analysis of biological parameters with respect to crop growth stages consequent to herbicide application.