Land preparation and Seed sowing
The land was prepared at ‘joe’ condition by deep ploughing and cross-ploughing 4 times by power tiller followed by laddering until the desired tilth. All the weeds, residues and stubbles of the previous crops were removed from the field and the large clods were broken into smaller pieces to obtain a desirable tilth of soil for sowing of mungbean seeds. BARI Mung-6 was used as experimental material and was sown on 31 January at the rate of 30 kg/ha (BARI, 2011) with making rows maintaining spacing (30 cm x 10 cm) for mungbean cultivation. Seed sowing was done at a depth of 6-7 cm and the seeds were covered by loose soil with the help of hand.
Fertilizer dose and Intercultural operations
The fertilizers were applied as per fertilizers recommendation guide (BARI, 2011). Urea, TSP and MoP were applied in the field uniformly @ 50-85-35 kg/ha, respectively during the final land preparation. The fertilizers were then mixed properly with the soil by spading and individual unit experimental plots were leveled. All intercultural operations were done as and when necessary to ensure normal growth and development of crops.
The insecticidal treatment combination arrangement of the experiment
The experiment comprised four treatment combinations of various insecticides including an untreated control. The treatment combinations of the experiment were assigned as follows: (1) TC1 = Chlorpyrifos + Cypermethrin (Nitro 505EC) @ 1 ml/L of water + Azadirachtin (Bioneem plus 1EC) @ 1 ml/L of water; (2) TC2 = Thiamethoxam + Chlorantraniliprole (Voliam flexi 300SC) @ 0.5 ml/L of water + Azadirachtin (Bioneem plus 1EC) @ 1 ml/L of water; (3) TC3 = Chlorpyrifos + Cypermethrin (Nitro 505EC) @ 1 ml/L of water + Spinosad (Tracer 45SC) @ 0.3 ml/L of water; (4) TC4 = Thiamethoxam + Chlorantraniliprole (Voliam flexi 300SC) @ 0.5 ml/L of water + Spinosad (Tracer 45SC) @ 0.3 ml/L of water; (5) TC0 = Untreated control (water spray @ 500 l/ha).
Procedure of spray application
The spray solutions at the pre-fixed concentration of the respective treatment combinations were prepared in Knapsack sprayer by mixing with water as required just before spraying. The spray solutions were sprayed in the assigned plots as per the package design. The first insecticide was sprayed afterwards the second insecticide was sprayed at three days interval as per package design. The spraying was always done in the afternoon to avoid bright sunlight. The spray was done uniformly to obtain complete coverage of whole plants of the assigned plots. Caution was taken to avoid any drift of the spray mixture to the adjacent plots at the time of the spray.
Data collection
The data were recorded from incidence of thrips, gram pod borer and legume pod borer during different growth stages of the crop. Number of thrips, gram pod borer and legume pod borer was recorded at flowering stage and podding stage. The data on the population of thrips, gram pod borer and legume pod borer were collected before and after 1 day of spray application from each unit plot. Thrips population was assessed from 10 open flowers which were randomly collected from two rows of each side of the plot avoiding border and central four rows. The collected flowers were immediately opened on the white paper and counted the thrips. The selected 1m2 (1m x 1m) area of the center of each unit plot was kept undisturbed for recording yield data. Grains were recorded from 1 m2 area per plot wise and the yield was expressed in kg/ha.
Calculating of % pod infestation
For collecting data on the percentage of pod borer infested pods, the number of infested pods and the total number of pods from randomly selected 10 plants from each unit plot were counted at ripening stage and recorded. The following formula was used for taking the infestation percentage:
Total number of infested pods
% Pod infestation = x 100
Total number of pods
Calculating of marginal benefit cost ratio (MBCR)
The marginal benefit cost ratio (MBCR) for each treatment combination was calculated on the basis of market price of mungbean, cost of insecticide and spraying. MBCR was measured by using the following formula described by Elias and Karim (1984).
Adjusted net return
Marginal Benefit Cost Ratio (MBCR) =
Total management cost
Statistical analysis: The collected data were statistically analyzed through the analysis of variance using Web Agri Stat Package (WASP 1.0). The population data were transformed to square root (√x + 0.5) values. Means were separated by critical difference (CD) values at 5% level of significance.