MSc

A series of field experiments were conducted in the Instructional Farm attached to the College of Agriculture, Vellayani, during 1984-85 for evaluating the bioefficacy of pesticide suspension/emulsions sprayed in varying volumes at different growth stages of rice crop for the control of various pests and diseases keeping the concentrations of the toxicants in the spray fluid at the recommended levels. A parallel series of experiments were conducted with similar volumes of spray fluids which were in different concentrations for maintaining the doses in all treatments at constant recommended level . the experiments were conducted in an area under bulk planting of rice (planted and maintained as per the package of practices recommended by the Kerala Agricultural University) by peg marking adequate number of plots at locations where pest incidence occurred in sufficient intensity. Randomised block design was adopted in all the experiments.
At tillering phase of the crop the incidence of the case worm, N.depunctalis, leaf roller C. medinalis and brown leaf spot disease were observed. Against N.depunctalis HCH suspension 0.2 percent was used in varying volumes in one experiment and the same at a fixed dose of 1.25 kg ai/ha and in varying volumes a parallel experiment. For the control of C. medinalis quinalphos 0.05 per cent emulsion was tried in varying volumes and the fixed dose of 0.25 kg ai/ha was also used in varying volumes. The treatment for the disease was with Dithane M 45 at a concentration of 0.4 per cent and at a dose of 2.0 kg/ha in similar range of volume. The volumes of spray fluid used were 300,350,400,450,500 and 550 1/ha and for each treatment there were three replications. Plots sprayed with water alone were retained as controls.
The results were assessed in terms of the reduction /increase in the populations of the pest or on the intensity of the damage caused by the pest, observed at different intervals after spraying. Results of the experiment showed that 350 1/ha was the optimum volume of spray fluid for the control of the pests and diseases occurring at tillering phase of the crop. In the second series of experiments where the recommended doses of toxicants per unit area were used in varying volumes of water the bioefficacy of the pesticides varied with the volumes of spray fluid used per unit area. At the tillering phase of the crop a formulation with 3501/ha of the water gave the maximum effect.
At bootleaf stage the crop was infested by the leaf roller C. medinalis and the stem borer S. incertulas. Quinalphos 0.05per cent emulsion was sprayed in varying volumes ranging from 450 to 700 1/ha. In both the experiments 550 1/ha of the spray fluid was found as the optimum volume with reference to the reduction in the extent of damage caused by the pests. Even when the quantity of pesticide applied per hectare was maintained at the fixed level of 0.25 kg ai the efficacy was varying with the volume of spray fluid used. The volume of 550 1/ha was found to be the optimum for the control of both the pests.
In the bootleaf stage the incidence of sheath blight and sheath rot were observed and for controlling the disease Bavistin 0.1% suspension was sprayed at varying volumes ranging from 450 to 700 1/ha. In another experiment the pesticide was applied in the same range of volumes but maintaining the dose at the fixed rate of 0.5kg/ha in all treatments. From the results 5501/ha could be fixed as the optimum volume for maximizing the bioefficacy of the pesticide against the two diseases.
The overall assessment of the data obtained from the experiments conducted at the bootleaf stage of the crop revealed that 550 1/ha of the spray fluid should be used for the control of the pests and diseases occurring at the stage and that the recommendation of a fixed quantity of pesticide per unit area will not be adequate unless it is used in 550 1/ha of water.
Only pest which occurred during the heading stage of the crop was the rice bug L. acuta . When methyl parathion 0.05% emulsion was applied at varying volumes ranging from 450 to 700 1/ha, 550 1/ha gave the highest initial reduction in population and maintained the effect up to the fifth day after treatment. Even when the quantity of insecticide was kept at a fixed dose of 0.25 kg ai/ha the volume of water to be used was found to be 550 1/ha for maximizing the bioefficacy of treatment.
In a separate series of experiments the influence of varying volumes of spray fluid on the coverage and deposit formation on different growth stages of the crop was ascertained using safranin as tracer. The data showed that the volume required for maximum deposition at tillering , bootleaf and heading stages of the crop were 350, 550 and 5501/ha respectively. These volumes were corresponding with the volumes of pesticide formulations required for maximizing the bioefficacy against the pests at different growth stages of the crop.